The McCoy Diesels

by Adrian Duncan

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hover over the images for a description.

    The McCoy Products Co
    The 1953 McCoy "Duro-Glo" .049 Diesel
    The 1953 McCoy Duro-Glo .049 Diesel on Test
    The 1954 McCoy .049D Diesel
    The McCoy .049D on Test
    The 1954 McCoy "9" .099 cuin Diesel
    The McCoy "9" Diesel seen in Context
    The McCoy "9" Diesel on Test
    The Glow-Plug Descendants
    The McCoy Diesels Today

The model diesel engine is universally recognized as a wartime European innovation and there's no doubt that its practical application and long-term development were concentrated on the east side of the Atlantic Ocean. Generally speaking, most people who are interested in the history of engine development during the first post-war decade tend to think of Europe as the home of the post-war diesel and America as the bastion of glow-plug development.

It therefore comes as something of a surprise for many diesel fanciers to discover how many US manufacturers actually became involved with diesels during the ten-year period from 1946 through 1955. Moreover, a number of these designs possessed considerable merit by any standard. We've covered a fair sampling of them in previous articles on this site, including Drone, CIE, OK, Air-O, Speed Demon, and DeLong, although the latter never saw production. Time now to look at yet another notable series of model diesels which originated in North America—the McCoy diesels.

These well-made and in some ways innovative engines caused quite a stir when they first appeared in the USA in early 1953, and an amazing number of old-timers still remember them today with great affection. They were the "first diesels" of many American modellers and were made in fairly large numbers, consequently remaining relatively available today on eBay and elsewhere. Hence any present-day engine aficionado wishing to give one a try should be able to gratify that desire. And as we shall see, the engines are unlikely to disappoint a well-informed owner!

Before getting started on our story, it's necessary to pay tribute once again to the dedication of our friend and colleague Tim Dannels, who has done so much to preserve the history of American model engines. It would be impossible to write with any authority about the products of any American manufacturer without consulting Tim's published writings, notably his invaluable American Model Engine Encyclopaedia. While accepting full responsibility for the content of the present article, I freely acknowledge my debt to Tim's efforts in the present instance.

The McCoy Products Co

The McCoy diesels were sold under the banner of the McCoy Products Co of Culver City, California, which is a west-side satellite community of greater Los Angeles. This company was of course identified with the legendary Dick McCoy, whose name surely needs no introduction to most model engine enthusiasts. A biography of Dick can be found elsewhere on this website.

Somewhat oddly, the McCoy diesels with which we are concerned here were not identified as products of the Duro-matic Products company which had manufactured the previous McCoy engines and with which Dick was associated as a designer. Rather, the manufacturers were named both on the boxes and on the instruction sheets as the McCoy Products Co of 8509 Higuera Street, Culver City, California.

The McCoy .049 "Duro-Glo" diesel model which introduced the McCoy diesel range was in fact the first product to be sold under the new company's banner, being placed on the market in early 1953. The engine's name hinted at its Duro-matic origins, and there's no doubt that it was in fact manufactured by Duro-matic—the guarantee card included with the engines was actually addressed to the Duro-matic Products Company at the same Higuera Street address! It should be recalled that Dick McCoy was still employed full-time at the HW Loud Machine Works Inc. as of 1953 and was therefore in no position to undertake large-scale commercial-scale model engine manufacture in his own right.

It would appear from this that the McCoy Products Company was simply a division of Duro-matic. The details remain unclear, but it's likely that the creation of this new division was somehow related to the developing relationship between Duro-matic and the Testor Corporation. Discussions between the two companies had commenced in 1949, resulting initially in an agreement under which the McCoy engines and the Testor flying model aircraft kits would be expressly designed to be mutually compatible and would be jointly marketed. This association was eventually to result in the outright acquisition of the Duro-matic Products Company by Testor in 1955, at which time Duro-matic President Charles D. Miller became Testor's Vice-President in charge of manufacturing, eventually becoming Testor's President in 1963.

Dick McCoy's role as engine design and production consultant was unaffected by this change in corporate ownership. It's an interesting fact that Dick was never at any time an actual employee of the Duro-matic company or of the successor Testor Corporation. He lent his name to the engines and served as their engine designer and production advisor, being paid pro rata for his services as they were provided, but was not directly involved in their manufacturing activities. His full-time job until 1956 remained with Loud's, after which he joined his sons Carl and Harold in building up their ultimately very successful C&H Products business.

Returning to 1952, it's not known what motivated then 45-year old Dick McCoy to turn his hand to diesel designing in the latter part of that year. American modelling was almost completely dominated by glow-plug engines at this time, and had been for some years. We saw earlier that there had been a number of American diesels in the past bearing names such as Drone, C.I.E., Micro, Mite, DeLong, Vivell, Speed Demon, Edco and the infamous Deezil. Some of these engines had been second to none in terms of quality and performance. However, none of them had been able to survive the glow-plug onslaught which began in earnest in 1948.

So why did Dick McCoy decide to turn back the clock and re-introduce the diesel into American modelling after a 4-year hiatus? The answer is most likely to be found in the realm of the most basic of all model engine attributes—performance. Dick McCoy was first and foremost a designer of high-performance engines. It could not have escaped his notice that as of 1952 great strides had been made in European diesel design and fuel technology, to the point where in the smaller displacements and for purposes other than all-out speed competition the diesel was then widely viewed outside America as the superior type of powerplant. Anything that promised higher performance was bound to attract the interest of someone like Dick McCoy!

Dick therefore set out to design a diesel engine in the popular 1/2-A .049 cu in. displacement category which would raise the performance bar in that category by the standards of the day. As events were to prove, he succeeded very well indeed in achieving this goal! Let's take a close look at his first diesel design to see how he went about it...

The 1953 McCoy "Duro-Glo" .049 Diesel

One of the more interesting aspects of the original 1953 version of the McCoy .049 Duro-Glo diesel was the fact that despite its name, it was not simply a conversion of an existing glow-pug model. The only previous McCoy .049 model was the 1951 "Baby Mac" glow-plug motor. The design of the new diesel incorporated a number of features carried over from its glow-plug predecessor, but there were enough differences to justify the view that this was an entirely new model rather than a simple glow-to-diesel conversion. As matters turned out, the original Duro-Glo diesel never appeared in glow-plug guise at any time.

Bore and stroke of the new model were 0.405 in (10.29 mm) and 0.386 in (9.80 mm) respectively for a displacement of 0.0497 cuin (0.815 cc). The claimed weight was a commendably light 1.5 ounces (42.5 gm), which checks out exactly on an actual example. Recommended airscrews were 6x4 for break-in, stunt and free flight, 5-1/2x4 for speed and 7x4 for radio control.

Among the most impressive features of the McCoy Duro-Glo .049 diesel were its compact size and notably light weigh for a diesel of its displacement. In fact, it was very little bulkier than the contemporary 0.55 cc Allbon Dart Mk I and weighed only 7.5 gm more than the Dart's 35 gm despite having a 47% displacement advantage.

The attached exploded view (taken from the manufacturer's instruction sheet) shows the main structural features of the engine. It was built around a pressure die-cast crankcase which was generally similar to that of the earlier "Baby Mac" from the deck down but dispensed with the integrally-cast exhaust stack. In fact, it appears that the crankcase of the Duro-Glo was produced from a modified Baby Mac die with the identification changed and the stack omitted. It even retained the dummy "bypass bulge" on the left-hand side of the case. Like the Baby Mac, it was arranged for radial mounting only.

The cylinder of the new model was a radially-ported screw-in item like that of its predecessor but did not feature the integrally-machined cooling fins of the earlier glow-plug model. Instead, a red-anodized aluminium alloy cooling jacket was used which screwed onto the externally threaded upper cylinder liner. The red cylinder jacket and chemically-blackened cylinder flange set off the highly polished crankcase casting nicely, resulting in a very handsome-looking unit.

The new engine incorporated several features in its upper cylinder design which were innovations at the time in a diesel context, albeit copied later by others. For one thing, the steel contra-piston was not lapped into the cylinder in the conventional manner but instead was an easy push fit. A seal was achieved through the use of a high-temperature O-ring which was mounted in a groove cut around the working surface of the contra-piston. Examination of the exploded view included above should clarify this feature.

Naturally, this system left the contra-piston free to move very easily in the cylinder—the usual "stiction" of a lapped contra-piston was completely absent. This required the provision of some means of ensuring that the engine would hold its compression settings while running. To deal with this issue, a fibre insert was fitted inside the cylinder jacket immediately below the compression screw hole. This gripped the compression screw sufficiently tightly that the engine held its settings dependably while remaining very easily adjustable at all times.

These features were later successfully transferred to the OK diesels in America as well as the FROG 80 Mk I diesel in Britain. The one downside of this system was the loss of the usual "feel" of a lapped contra piston. Many diesel modellers found this quite hard to get used to. That said, there's no doubt at all that the system worked extremely well once one became accustomed to it.

The unhardened chemically-blackened steel cylinder featured three sawn exhaust ports cut in the locating flange machined integrally at the mid-point of the cylinder. This flange served to locate the screw-in cylinder vertically in the case. Three sawn transfer ports were cut through the cylinder wall immediately below the flange.

The disadvantage of this then-common porting arrangement is that no overlap can be provided between the exhaust and transfer ports—in fact, the transfer opening has to lag well behind the exhaust, giving an inescapably lengthy blow-down period. Consequently, it's necessary to arrange things so that the exhaust opens relatively early in order to provide a sufficiently long transfer period. The McCoy .049 Duro-Glo was of course no exception to this requirement. Exhaust period was unusually long at around 155 degrees, but even so the transfer period was only of the order of 100 degrees or so. However, transfer port area was quite large due to the 360 degree layout, and the engine's performance clearly showed that this transfer period was adequate for practical purposes.

The cylinder screwed into the crankcase in conventional fashion, seating on a fibre washer which ensured a good seal. The female cylinder installation thread in the upper crankcase was cut to a considerably smaller diameter than the outer diameter of the case and was interrupted on both sides to create a pair of relatively deep bypass channels having adequate cross-sectional area. The upper portions of both the outer cylinder wall below the flange and the upper crankcase above the cylinder installation threads were relieved and left plain. This resulted in an unthreaded annular passage completely surrounding the cylinder wall at transfer port level. This annular passage was supplied with mixture by the two bypass passages mentioned earlier and in turn fed the three transfer ports. The apparent bypass passage which was externally visible on the left side of the crankcase casting was in fact a dummy, serving no functional purpose.

This system closely mirrored that which had been introduced in 1949 on the original OK Cub .049 model, the sole exception being the use of sawn transfer ports instead of the upwardly-angled drilled ports employed by OK. Presumably this was how McCoy got around the patent held by Charles Brebeck with respect to the OK system. The great advantage of this arrangement was the fact that transfer efficiency was essentially unaffected by the annular position in which the screw-in cylinder ended up when tightened.

The hardened steel piston had an unusually short skirt length, resulting in a significant period of sub-piston induction around top dead centre. A solid bronze gudgeon pin was used in conjunction with a turned aluminium alloy connecting rod of the familiar "dog bone" pattern. The small end "ball" was of quite generous dimensions and gave excellent support—a very good feature which was overlooked on some rods of this type.

The crankshaft was a one-piece hardened steel item having a full-disc counterbalanced crankweb. Journal diameter was 0.218 in. with an internal gas passage having a diameter of 0.125 in. In hindsight, a somewhat larger main journal diameter might have been a good feature in terms of strength, a fact which McCoy themselves were soon to recognize. The shaft was an excellent fit in the plain main bearing. The prop driver was a simple turning in light alloy which was pressed onto a splined section of the shaft forward of the main journal. A standard nut and washer were used to secure the prop on an 8-32 thread.

On the original models, the crankshaft induction port was a compound opening consisting of a 0.125 in. diameter round hole in the centre of a milled "flat" in the journal surface. This gave quite rapid and hence efficient opening and closing of the induction system at the expense of introducing two sharp-angled "steps" into the port configuration. These acted as stress raisers and hence weakened the shaft rather more than a simple round hole would have done. To aggravate this problem, the shaft was apparently quench-hardened to a somewhat brittle state and was not stress-relieved afterwards.

As a result, the early examples fitted with this shaft proved to be unduly prone to shaft breakage at the induction port location, especially if the engine ever got into an over-compressed state, as most diesels do at one time or another. The prevalence of this issue was such that the company soon moved to change the design, producing the flat area surrounding the induction hole using a concentric circular cutter (probably integral with the drill) rather than by transverse milling. In addition, all edges and corners were carefully rounded off. The resulting opening created far less of a stress-raiser in the shaft. Coupled with changes in the material and heat treatment specifications, this resulted in the engines becoming far more reliable, possibly at some expense in terms of performance.

The intake venturi was cast in unit with the crankcase and main bearing. In typical American 1/2-A fashion for the day, the brass spraybar was simply pressed into the transverse hole provided for it across the venturi. The spraybar was internally threaded 1-72 to accommodate a hard brass needle having an integrally-machined serrated disc at its outer end for control purposes. The needle was very effectively tensioned using a simple coil spring.

It must be said that this needle design always stood out as one of the fundamental weaknesses of the design from a practical standpoint. For one thing, the needle was angled back to the right, which made it impossible to re-install it on the left for convenient sidewinder mounting in a control-line application. For another, the needle itself was extremely vulnerable to damage in a crash. Moreover, if it broke off at the end of the spraybar (as it usually did), extraction of the portion of the needle within the spraybar could be problematic.

On the plus side, the 72 TPI thread coupled with a relatively fine needle taper meant that mixture control was unusually precise—a very good feature in performance terms. It's also true that the rearward-angled needle improved the accessibility of the control to a marked degree.

The engine was completed by a pressure die-cast backplate which was secured to the case by the same pair of long 2-56 screws that were used for radial mounting. A gasket was used to create a seal. No tank was provided for this engine at any time. When un-mounted, the unit was held together using two nuts on the mounting screws.

This engine created quite a stir in America when it first appeared during early 1953. It was similar in style to the then-familiar Atwood.049 glow-plug models and weighted more or less the same as them. This imparted an air of comfortable familiarity for many American modellers. However, the little McCoy outperformed most of its rivals by some margin and was also noted for its easy starting. Its outstanding characteristic was its ability to turn relatively large airscrews quite comfortably, a characteristic of diesels due to the precise ignition timing control allowed by the variable compression feature.

These attributes were quickly recognized by the American contest fraternity, with the result that the McCoy Duro-Glo diesel soon became a serious contender for all forms of 1/2-A competition other than all-out speed. The one downside was that its crankshaft remained perhaps a little under-designed for the power that it produced—as we saw earlier, the initial engines with compound induction ports were known for breaking crankshafts, especially if run at all over-compressed. Even the later models with their redesigned crankshafts were not entirely immune to this problem, although they were far better. With practised handling, though, many of them seemed to keep running forever!

The 1953 McCoy Duro-Glo .049 Diesel on Test

The impact of the McCoy Duro-Glo .049 diesel is perhaps best illustrated by the fact that it appeared in no fewer than four published tests during its first year of production! This must surely make it one of the most extensively-tested model engines of them all! In order of their publication, these tests were as follows:

  1. Flying Models, August 1953
  2. Model Airplane News, August 1953
  3. Aeromodeller, October 1953
  4. Model Aircraft, January 1954

Given the sheer mass of material represented by these tests, the best that we can do here is summarize the findings of a few of these reviews in the order in which they appeared.

The August 1953 Flying Models review (from their semi-regular Logging the Motor Mart column is un-attributed, as that appearing the at the same time in the rival publication, Model Airplane News. However, there is little doubt that the MAN review author was EC "Ted" Martin of AMCO fame. Ted emigrated from England to Canada in 1952 and had become the chief engine tester for Model Airplane News in December of that year.

In keeping with the US style of magazines at the time, both tests were aggravatingly fragmented throughout the issue in question, so we have confined ourselves to reproducing the two MAN pages on which the McCoy .049 diesel was actually discussed. Martin (assuming it was he) began by summarizing the course of model diesel history in the United States up to his time of writing. He noted that in Europe the diesel was considered superior to the glow-plug engine for many modelling applications, and clearly felt that it was this fact which had prompted the appearance of the McCoy diesel. Recognizing the unfamiliarity of many American modellers with diesels, he then embarked upon a quite lengthy discussion of the principles of design and operation of the model diesel as well as the nature of its special fuel requirements.

Martin was an unswerving advocate of the use of diesels by North American modellers. It's worth recalling in passing that one of his ambitions in relocating from England to North America had been to enter into production with a high-performance 1/2-A diesel design of his own. For one reason or another, this project never got off the ground, and the appearance of the McCoy Duro-Glo .049 diesel only a year later to such acclaim may well have given rise to a few pangs of regret over the missed opportunity on Martin's part!

In his test report, Martin did as much as he could to encourage American modellers to give diesel engines a try. His "oily-hands" advocacy didn't stop with this test—the September 1953 issue of Model Airplane News carried a most informative article by Martin entitled "Know Your Diesels" in which he went into even greater detail regarding the mysteries of diesel operation. The McCoy Duro-Glo .049 diesel was featured as the heading illustration for this article, although the sectional view of a "typical diesel" on the second page shows Martin's famous AMCO 3.5 BB design, an engine almost completely replicated as the MAN 19, a machine-from-solid DIY project by Martin for MAN which commenced in the April 1956 issue.

As a result of its high advocacy content, very little of the test report on the McCoy Duro-Glo .049 diesel was devoted to an appraisal of the engine itself—in fact, Martin's rather brief comments on this topic were tacked on at the end more or less as an afterthought! He confined himself to stating that the engine "ran well and smoothly with positive control response at all times" and that "starting was easy, hot or cold, and on all prop sizes". The report did not include the publication of actual torque or BHP figures, but the prop-rpm figures given were pretty impressive by then-current standards. Typical figures included 13,000 rpm on a Top Flite 6x4, 13,200 rpm on a Power Prop 6x4, 14,100 rpm on a Top Flite 6x3 and 15,500 rpm on a Power Prop 6x3. These figures seem entirely consistent with the manufacturer's prop recommendations quoted earlier.

Martin reported no mechanical failures during the course of his test. By contrast, Aeromodeller tester Ron Warring ran head-on into the crankshaft breakage issue mentioned in our earlier description of this model. In his October 1953 test report, Warring noted that his example had the original shaft with the compound induction port, and reported that it failed in service by fracturing at the induction port after a few hours' running. Prior to this mishap, Warring had more or less completed his testing of the engine and he placed it in the "I want" class despite the failure, praising its starting and running qualities to the skies along with its quality of construction. His published power curve suggested an output of around 0.079 BHP @ 12,500 rpm—a very impressive figure indeed by the standards of the day for a 0.81 cc diesel. The soon-to-be competing 0.76 cc Allbon Merlin only managed a measured output of 0.058 BHP @ 13,000 rpm in its subsequent test by Warring which appeared in the December 1954 issue of Aeromodeller.

Warring wrote to the manufacturers concerning the crankshaft breakage issue and received a prompt response to his inquiry. He played fair with the manufacturers by actually publishing the main text of their response along with his own test report. This read as follows:

" [We wish to] assure you that your deduction that the cause was incorrect material was quite accurate. The material has been changed: the heat treat specifications have been carefully engineered: the method of removing the sharp corner at the intake has been corrected to assure greater strength at that point ... we are shipping to you a new crankshaft to replace the one damaged in the test".

Warring stated that the new crankshaft reflected the comments in McCoy's letter, and assured his readers that no further trouble should be experienced with broken crankshafts. Later experience showed that the revised shaft was indeed considerably more durable, although some breakages reportedly continued to occur as a result of mis-handling of the engine.

The 1954 McCoy .049D Diesel

The McCoy Duro-Glo .049 diesel continued in production into 1954. The "Duro-Glo" designation was dropped fairly early on from the boxes and the advertising, with the engine being promoted and sold by the name "McCoy .049 diesel". However, the crankcase die was unaltered and hence the Duro-Glo designation continued to appear on the left side of the crankcase. Sales continued to be more than sufficient to justify continued production.

However, there is evidence to suggest that the change from the original crankshaft with its efficient but weak compound induction port to a round opening had an adverse effect on the performance of the Duro-Glo, exactly as we might expect. Given this state of affairs, Dick McCoy decided to see what might be done to improve the engine still further. From a design perspective, the obvious areas in which further development seemed possible were the strength of the crankshaft and the efficiency of the induction system.

Accordingly, Dick drew up a design for a revised version of the .049 diesel which incorporated a larger diameter crankshaft. This achieved two things—one, it made the shaft considerably stronger; and two, it allowed the use of a larger-diameter internal gas passage within the shaft. The revised shaft had a nominal journal diameter of 0.250 in., with a central gas passage diameter of 0.157 in. These changes might reasonably be expected to improve both the engine's durability and its top-end performance.

The new model appeared in the latter part of 1954. It was generally referred to as the McCoy .049D—the Duro-Glo designation had now been dropped altogether. It featured a completely revised crankcase which was arranged for beam mounting only. The former radial mounting lugs were no longer present, and the backplate was now a screw-in item. The early cases had a polished finish like that of the previous radial-mount model, but this was later changed to a matte finish when the companion shiny-cased .049 glow-plug model appeared in 1955. The illustrated example is of this latter type.

For the first time, a back tank was supplied with the engine. This was a stamping from aluminium sheet and was left plain. Most examples had a single filler spigot, the location of which varied throughout the production run. A few of the later models, like the one illustrated, had two filler spigots, which actually made filling a lot more convenient.

This variant of the engine also featured a slightly modified cylinder. The original "Duro-Glo" model had no integral cooling fins above the exhaust port flange. The revised cylinder had a single integrally-machined cooling fin above the exhaust flange, similar in style to the contemporary Wen-Mac models. The engine continued to feature the same type of O-ring contra-piston and screw-on red-anodized cooling jacket with fibre insert for retention of settings. The same type of needle valve assembly was also carried over from the previous model. However, the really unique feature of the new model was the inclusion of a separate venturi insert which incorporated a spring-loaded poppet valve. This unit was retained in position by the spraybar, which continued to be of the pressed-in type.

The valve consisted of a square-section plunger which bore against an internal lip formed a little below the venturi mouth and was held in that position by a very light spring. The square section of the plunger in the circular lower venturi bore retained the plunger in a central location within the bore while allowing the passage of gas past the plunger when the valve was open.

This unit worked in a similar fashion to the more familiar reed valve in that it responded to variations in crankcase pressure by allowing gas to pass into the venturi when crankcase pressure was reduced below atmospheric but not allowing gas to escape in the opposite direction when internal gas pressure increased above that point. In short, it eliminated any possibility of induction blow-back, particularly at low speeds.

Now the inclusion of a poppet valve in the induction system of a conventional crankshaft front rotary valve engine seems at best superfluous and at worst a definite impediment to performance in view of the inevitable venturi restriction imposed by the physical presence of the valve. Here we have to recall the fact that the engine retained a pretty massive helping of sub-piston induction—some 40 degrees of crankshaft rotation. This meant that much of the crankcase filling during the induction phase took place by way of the exhaust ports. In such a design, the main function of the rotary valve induction phase was to induce sufficient fuel into the crankcase—any shortfall in overall gas filling would be made up during the sub-piston induction phase.

But even so, the presence of the poppet valve undeniably represented a restriction upon the engine's induction capacity despite the contribution of the sub-piston induction. So why was it included, given the fact that induction was timed by the crankshaft rotary valve in any case? The only rational answer that I can come up with is the notion that the makers wanted to improve handling and flexibility by eliminating any possibility of blowback through the fuel induction system during starting and at low speeds as well as improving suction to some degree. It is also possible that the device was included simply as a sales gimmick, but I for one would like to think that any feature seen on a Dick McCoy design must have had some performance-based objective.

In actually fact, we shall see later that the device was ineffective in performance terms—it did improve starting suction to some extent, but the engine's high-speed performance was actually significantly better without it, as one might expect. Accordingly, quite a few owners removed the poppet valve, which explains why many examples today which were originally so equipped are missing this device.

It would seem that the McCoy Products Company came to agree with this assessment, since it wasn't too long before a second variant of the .049D appeared on the market. This version of the engine is distinguished from the original model by the fact that it had a matte-finished crankcase in place of the polished item originally used. It also lacked the poppet valve in the induction system. In addition, many examples reverted to the type of cylinder seen on the original "Duro-Glo" model, with no extra integral cooling fin above the exhaust port belt. In all other respects, the two variants were identical. The illustrated example is of this second type.

The result of the above redesign was a far sturdier engine that enjoyed a significantly higher performance potential than its predecessor. The later models without the poppet valve would in fact run at speeds which were almost comparable with those reached by the standard-setting Cox .049 Thermal Hopper glow-plug model. The McCoy .049 diesel thus retained its position as a serious 1/2-A contest contender. Its strong suit was the fact that it would happily turn a larger and hence more efficient airscrew than most of the opposition. This latter characteristic resulted for a time in its becoming the engine to use in the free-flight PAA-load class which was then extremely popular.

The McCoy .049D on Test

The McCoy .049D attracted far less attention than its Duro-Glo predecessor, appearing in only one published test report as far as I can determine. This test appeared in the August 1955 issue of Model Airplane News. This time, the name of Ted Martin did appear as the tester.

Unusually, this test report covered no fewer than four distinct McCoy models which had then recently been released. In addition to the McCoy .049D, these included the companion McCoy .049 glow model as well as the .29 cuin and .36 cuin "Super Stunt" models. In actual fact, the two McCoy .049 models covered in this test had been released in 1954, as had the McCoy 29 "Super Stunt" model. The only really recent release covered by this article was the short-lived 36 "Super Stunt" model. It appears from this that the reported testing had taken place over a considerable period of time.

In terms of his coverage of the McCoy .049D, Martin was extremely complimentary. He was clearly impressed with the logic behind the poppet valve in the intake, stating that its effect was to offset the starting disadvantages of the high-speed induction timing resulting from the geometric design of the engine's mechanical components. He theorized that the tension of the very light spring used in the poppet valve was carefully engineered so that the valve would close fairly early at low speeds during the crankcase compression phase (presumably well before the rotary valve closed) but would permanently "float" at high speeds due to induction flow, thus allowing the crankshaft timing to become the controlling factor.

If this state of affairs could actually be achieved, we would have in effect a reed valve engine with pressure-controlled induction timing at low speeds and a rotary valve engine with mechanically-controlled timing at higher speeds. Martin saw this as offering a path towards a truly general-purpose engine, since the variable ignition timing available in a variable-compression model diesel did undoubtedly allow a very wide range of operating speeds.

Martin expressed his doubts regarding the overall effect of this valve on ultimate volumetric efficiency—he recognized that even when fully open the valve represented a physical obstruction in the venturi. However, he went on to state that the performance obtained was such as to relieve any doubts regarding this point. Here I can only comment that if Martin was impressed with the engine's performance with the poppet valve fitted, he would have been amazed at the results to be had with the valve removed! It's actually a bit astonishing that he didn't try this experiment ……Dick McCoy certainly did!

Martin commented that the poppet valve was extremely effective in promoting easy starting. No prime was apparently required, and the compression setting was found to be quite non-critical. Martin commented that the diesel .049 model seemed if anything "even more anxious to start" than its glow counterpart tested at the same time, and expressed his doubt that there was "any more easily starting diesel design in existence".

Once again, no torque or power curves were extracted, but a full set of prop/rpm figures were given. These offer us a very interesting comparison between the reported performances of the McCoy .049D and the .049 Duro-Glo tested a year previously in the same series.

PropellerMcCoy 049 Dura-GloMcCoy 049D
Power Prop 6x512,00011,200
Top Flite 6x511,60010,250
Power Prop 6x413,20012,400
Top Flite 6x413,00011,600
Power Prop 6x315,50014,700
Top Flite 6x314,10013,750
Power Prop 5-1/4 x414,60014,250
Power Prop 5-1/4 x316,00014,800

As can be clearly seen, the original McCoy .049 Duro-Glo handily beat the "updated" McCoy .049D with its poppet valve on all props tested! It appears extremely odd that this fact was unreported or perhaps unnoticed by Ted Martin. Despite having a larger crankshaft with more open timing, on this showing the .049D was clearly an inferior performer to the earlier .049 Duro-Glo which it replaced! It's very difficult to identify any other potential culprit than the infamous poppet valve.

Thankfully, this matter was set straight by none other than the late and much-missed Ron Moulton, who conducted a series of prop-rpm tests on the most popular 1/2-A diesels and glow-plug motors of the mid-1950's using a standard family of airscrews of the types then in general use. A summary of these tests appeared in Ron's 1958 compilation Model Aero Engine Encyclopaedia.

The results of these tests conducted by the same individual using the same props stand as an invaluable comparison of the relative performances of the various models. For the purposes of this article, we can do no better than present Ron's findings for both the McCoy Duro-Glo and beam-mount .049D models together with one of the accepted British "standards" of the day—the ubiquitous Allbon Merlin. For comparison purposes, it's also instructive to include the figures obtained for the "gold standard" 1/2-A performer of the time—the Cox Thermal Hopper glow-plug model.

Ron made no attempt to measure actual power outputs during this series of tests. Rather, he simply checked the rpm reached by each of the engines on the same family of airscrews. Assuming that the same airscrews and means of rev checking were used throughout, the results should be directly comparable.

PropellerAllbon MerlinMcCoy 049McCoy 049DCox Thermal Hopper
Tiger 8x3-1/26,8006,6006,8007,200
Stant 7x48,2008,1009,0009,900
Tornado 7x49,2009,00010,10010,900
Stant 6x411,40011,20012,00012,800
KeilKraft 6x412,00011,75013,20014,000
E.D. 6x412,20012,00013,40014,400
Frog 6x4 12,50012,80013,60014,600
Tornado 6x313,50013,20014,25016,400
Trucut 5x313,60013,30015,20017,000
Kaysun 5-1/2x2-1/2 15,80015,50018,00020,400

The above table makes it clear that the original McCoy .049 Duro-Glo showed itself to be more or less on a par with the D-C Merlin. This in itself is an interesting finding in view of Ron Warring's earlier tests on the two engines, which had found that the original Duro-Glo was a considerably stronger performer than the Merlin. My own experience with the two engines also implies that the Duro-Glo has an appreciable edge over the Merlin.

It would appear that Ron Moulton may well have tested an example of the Duro-Glo with the revised crankshaft, which had a round induction port instead of the more efficient but far weaker compound opening. It's a reasonable inference that the change to a less efficient induction port may in fact have reduced performance to a noticeable extent.

However, Ron's figures confirm that his example of the revised McCoy .049D with its larger shaft was a far stronger performer than both the Duro-Glo and the Merlin, and was actually not all that far behind the all-conquering Cox Thermal Hopper glow-plug model until speeds got up past the 14,000 rpm range or thereabouts. More importantly, the figures obtained by Ron for the .049D bear no resemblance whatsoever to those reported by Ted Martin—the differences are simply too great to be explained by the fact that different families of airscrews were involved.

The inescapable inference is that Ron tested one of the later examples of the .049D with the poppet valve eliminated in favour of a conventional open venturi. If ever there was a graphic demonstration of the stifling effect of the poppet valve, this was it! Martin had found the .049D to be a significantly inferior performer to the .049 Duro-Glo—Moulton found the direct opposite.

If Ted Martin seemingly failed to pick up on the implications of the results reported in Model Airplane News, the McCoy Products Company certainly did not, and nether did their customers. The company soon began selling the engine with the poppet valve eliminated, a step which many of their customers had already taken. In this form, the McCoy .049D was almost certainly one of the highest-performance commercial 1/2-A diesel designs of its day, with only the outstanding Super-Tigre G29 being a possible rival at the time. A very commendable effort indeed on the part of Dick McCoy! Too bad that these engines never became readily available in Britain and elsewhere ...!

The 1954 McCoy "9" .099 cuin Diesel

During the latter part of 1954, more or less concurrently with the introduction of the revised McCoy .049 diesel just described, the McCoy Products Company also released a .099 cu. in version of what was in effect the same engine. This was known as the McCoy "9" diesel, and was billed as "America's most powerful diesel engine", which it undoubtedly was at the time of its release. To all intents and purposes, it was simply a scaled-up version of its smaller beam-mount relative, albeit thankfully omitting the poppet valve in the integrally-cast intake venturi, which had no insert.

Bore and stroke of the McCoy "9" diesel were 0.526 in. (13.36 mm) and 0.460 in. (11.68 mm) respectively for a displacement of 0.0999 cuin (1.637 cc). This was right on the class limit of 0.10 cuin and was slightly at odds with the manufacturer's cited displacement of .098 cu. in., but we needn't quibble about that at this point in time! Claimed weight was 3 ounces even, but my own illustrated LN example turns the scale at 3.17 ounces (90 gm) with tank and fuel tubing. Bare weight without tank checks out at 85 gm—more or less 3 ounces exactly. Manufacturer's recommended airscrews for this engine were 9x4 for break-in, 8x6 for stunt, 7x8 for speed and 9x4 for radio control and free flight.

In terms of its construction, the attached exploded view will confirm that the McCoy "9" was more or less identical to its smaller companion in the range. The material specification too was identical. Accordingly, the foregoing description of the smaller model is equally applicable, and there's no need to say more on that subject here.

Like its 1/2-A stablemate, the "9" was a very good-looking unit with its red cooling jacket, chemically-blackened cylinder flange and highly polished castings. It was also very well made indeed and "felt" good right out of the box. Structurally, it was very sturdy and held up extremely well in service, with no reports of any significant weaknesses other than the vulnerability of the needle valve. In particular, I can find no reports of the crankshaft failure issue which had plagued the earlier McCoy Duro-Glo .049 diesel model.

The engine was very attractively packaged in a large box with a fold-out top that allowed the engine to be displayed to good advantage in its box. Interestingly, the cutaways in the box inserts for both of my NIB examples do not make provision for the tank. It seems that the tank was supplied unattached to the engine and that its mounting on the engine was an option left to the purchaser.

During its all-too brief production lifetime there were a few relatively minor changes. The needle valve used on the earlier examples was an over-long and very vulnerable steel wire unit which was externally threaded to mate with an internally-threaded pressed-in spraybar. Tension was provided by a split in the needle end of the spraybar. This didn't remain effective in service for very long, and a switch was later made to a spring-tensioned unit which was to all intents and purposes identical in design to that used on the companion .049 model and provided far more stable needle settings.

The tank too was slightly changed. The earlier tanks were a little larger with smooth profiles along their full length, while the later tanks were slightly smaller in diameter and had a flange around the open end to restore sufficient diameter for mounting on the engine backplate. The illustrated example is of the latter type.

Otherwise, the engine remained unchanged throughout its production life. This, alas, was to be all too short—although the McCoy "9" seems to have remained in production well into 1955, it appears certain that its manufacture had been discontinued by the end of that year. The relative numbers of present-day survivors imply that production figures for the "9" never matched those for its smaller 1/2-A companion in the range.

The McCoy "9" Diesel seen in Context

The McCoy "9" diesel appears to have completely escaped the attentions of the published model engine testers of the day. This is a great pity, because it was a really excellent design which was built to the highest standards and would undoubtedly have stood up very well to comparison with any of its contemporaries, regardless of origin. There's little question that it would have sold well in Europe if it had ever been exported to that region.

Some idea of the qualities of this model may be gauged from the reaction of those "senior" modellers today who recall having used the McCoy "9" diesel during its heyday. The engine comes up regularly in discussions on the more popular modelling forums and, almost without exception, former users recall the McCoy "9" as having been one of the best small diesels that they ever experienced. They typically comment on its outstanding power output and dependability as well as its easy starting and smooth running characteristics. Those who also tried the competing OK Cub diesel models generally recall the McCoy models as being easier to get along with, although they were both heavier and bulkier than their OK rivals.

In a discussion thread a few years ago on a widely-read modelling forum, a number of participants conducted an unofficial poll to determine which were the best-running and most satisfactory .09 cuin diesels in their experience. The individuals who participated came from all around the world, including the USA, Britain, Australia and Canada, and the voting was open to any model diesel engine, regardless of age or origin. The engine which received the most votes was none other than the McCoy "9" diesel! One of the engine's biggest fans was in fact the legendary George Aldrich, who certainly knew his engines pretty well.

So here we have an engine which has consistently received the highest accolades from everyone who has ever had any experience with running one. How well-founded is this positive perception? Let's find out.

The McCoy "9" Diesel on Test

Having a slightly-used example of the McCoy "9" on hand, I saw no harm in putting it though its paces on the bench. The main issue was which design to use as a "control" for comparison purposes. In 1954, when the McCoy "9" appeared, engines such as the A-M 15 and FROG 150R had yet to appear. However, the plain-bearing Elfin 1.49 cc model was then still very much to the fore and was one of the more highly-regarded 1.5 cc diesels at the time, having made several impressive showings in International competition. It had actually won the 1952 World Free-Flight Championship and had finished a still-creditable fourth in the 1954 edition of the same contest. Peter Chinn found around 0.15 BHP at some 13,500 rpm in his August 1950 test of the engine for Model Aircraft, although he later admitted that not all examples reached this standard. .

Accordingly, I decided that I would put the McCoy up against a well run-in original example of the Elfin 149 PB which I had lying about. I also had a well-used example of the FROG 150 which was another of the "standard" 1.5 cc diesels in use in Britain at the time of the McCoy's introduction. This engine had performed well in its September 1951 Aeromodeller test, producing around 0.12 BHP at 13,000 rpm, and was still a favourite among British modellers in 1954.

The McCoy does admittedly enjoy a 10% displacement advantage over both the FROG and Elfin, but this could be accommodated by working to specific output figures in order to even things up. The Elfin is also a little lighter at 76 gm (2.68 ounces). However, anyone buying a McCoy "9" would probably install it in a model designed for a 1.5 cc diesel, so the comparison seemed fair to me.

The used example of the McCoy which I had available for test was in excellent original condition but had a shortened wire needle—a quite common modification given the excessive and somewhat awkward length of the standard item. As usual with this needle design following a period of use, the split at the end of the spraybar had ceased to be effective in terms of retaining needle settings, and I used a short piece of small-bore fuel tubing to remedy this problem. This simple fix proved very effective and can be recommended to any present-day owner.

I may as well come right out and say it—the McCoy simply astonished me with its performance! It proved to be a very easy starter indeed, requiring only a flick or two following a small prime after the fuel line was filled by choking. It was extremely responsive to both controls without being at all over-sensitive—optimum settings were easily established. Running was absolutely smooth and mis-free at all speeds, with no trace of sagging or any other form of distress at any time.

But most of all, it simply blew the other two contestants away in performance terms! Bad weather discouraged me from doing a complete range of props, but the following table speaks for itself. The numbers in brackets are implied BHP figures based on estimated power absorption coefficients for the airscrews in question.

PropellerMcCoy 9FROG 150Elfin 149
Taipan 9x4 GF 9,100 (0.135) 8,000 (0.092)8,600 (0.114)
APC 9x4 GF8,900 (0.131)7,800 (0.088)8,300 (0.106)
Taipan 8x6 GF9,000 (0.133)7,900 (0.090)8,400 (0.108)
APC 8x6 GF9,600 ( 0.145)8,400 (0.097)8,800 (0.112)
Taipan 8x4 GF 11,700 (0.165)10,100 (0.106)10,800 (0.130)
Taipan 7x4 GF13,600 (0.177)11,900 (0.119)12,600 (0.141)

An interesting comparison indeed! Both the FROG and the Elfin appear to have performed more or less in accordance with the published test figures for both engines. But look at the numbers for the McCoy! It simply buried the other two engines! The implied peak of around 0.180 BHP at somewhere in the vicinity of 14,000 rpm represents a specific output of around 0.11 BHP/cc. This is an a outstanding performance by the standards of 1954—a lot of contemporary plain-bearing 2.5 cc diesels barely topped the indicated BHP figure, and relatively few diesels of any specification and displacement could match this specific output at the time. In addition the power curve seems to be unusually flat, with good power remaining available as low as 9,000 rpm.

It's apparent from this that the McCoy "9" could more than hold its own against the European 1.5 cc opposition of its day. In fact, at the time of its release it was almost certainly one of the highest-performing diesels in its general displacement category, regardless of origin. It also handled superbly. I can see why so many people recall these engines in such a favourable light!

The McCoy 9's main problem in a competition context was the fact that it exceeded the European class 1/2-A limit of 1.5 cc by almost 10% and was therefore ineligible for use in that class. However, it would have been comparatively easy for McCoy to produce a "European" version with the same 0.460 in. (11.68 mm) stroke but a bore of, say, 0.500 in. (12.7 mm) instead of the standard 0.526 in. (13.36 mm), thus reducing the displacement to 1.48 cc in compliance with European 1/2-A rules. I'd bet that the resulting engine would still have been a very stout performer!

Even the engine's standard 1.637 cc displacement would have been no barrier to its use in International competition (2.5 cc limit) against such engines as the Elfin 149 which were then still in use in that context. Furthermore, to the vast majority of modellers who were not competition-oriented and just wished to enjoy their aeromodelling, the engine would have represented a more than acceptable choice for models intended for 1.5 cc engines. Looking at the above figures, I'd have loved to have owned one "back then" myself! Count me among the converts.

As a final comment on the above test results, it's apparent that the McCoy 9 could certainly swing a reasonably meaty prop with authority. However, in order to take advantage of its outstanding peak power output, it would be necessary to use somewhat smaller props than those recommended by the makers. Both the 9x4 and 8x6 props suggested in the instruction leaflet for free flight and control line respectively pull the engine down to speeds in the 9,000 rpm range on the bench. Even allowing for airborne pickup, the engine would be unlikely to reach peak in the air on these props. It appears that an 8x4 for free flight and a 7x6 for control line would produce better results in terms of ultimate airborne performance.

The Glow-Plug Descendants

Although the focus of this article is very much on the McCoy diesels, it seems appropriate for completeness to include a very brief comment on the glow-plug models which evolved from the diesels just described. Those interested solely in the diesel models should skip to the next section.

We noted earlier that despite its name, the original McCoy .049 Duro-Glo model never appeared in glow-plug form. The same can be said of the McCoy "9" diesel model. However, in early 1955 a glow-plug version of the beam-mount McCoy .049D was released. The development of a glow-plug variant was probably a marketing decision which was related to the imminent 1955 take-over of the Duro-matic Products Company and the McCoy engine range by the Testor Corporation.

The glow-plug version of the McCoy .049 had an appearance which was at first glance quite similar to that of the diesel version described earlier. However, it featured a completely redesigned Cox-influenced cylinder using twin opposed rectangular exhaust ports with twin internal transfer flutes between them. To accommodate the revised porting, the engines used a steel con-rod with a ball-and-socket small end bearing to eliminate any possibility of a gudgeon pin fouling a port.

The interruptions in the female cylinder installation thread in the crankcase were of course no longer required for bypass purposes and were therefore omitted. Hence the crankcases for the diesel and glow-plug models are not interchangeable despite their identical external appearance. The .049 glow-plug model featured a shiny case like the earlier diesel models. The companion .049D model which remained in production at this time had a matte-finished case.

The engine sported a red-anodized screw-on cooling jacket as before, but this now had a far larger hole where the compression screw was formerly located. A separate cylinder head with integral glow element was clamped to the top of the cylinder by this cooling jacket. A seal was ensured through the use of a heat-resistant vulcanized asbestos gasket.

Apart from the features just described, the 1955 McCoy .049 glow-plug model was essentially identical to its diesel stablemate. These engines were very good performers by the standards of the day. This model continued in production for some time after the diesel version had been dropped.

In 1958 it appeared in a slightly revised version known as the McCoy "5", which used a modified crankcase having both beam mounts and radial mounting lugs. The exhaust ports on this model were rounded rather than squared-off as before, but otherwise the two glow-plug models were essentially identical. The McCoy "5" was produced in considerably smaller numbers than the previous McCoy .049 model and is hence rather less commonly encountered nowadays.

The McCoy Diesels Today

As noted earlier, the McCoy diesels were made in sufficient numbers that a significant number of them survive today, many in quite good condition. Accordingly, anyone wishing to try one should have little difficulty in tracking down an example on eBay or elsewhere. The .099 cuin model is rather less commonly-encountered than either of the smaller .049 models and tends to sell for somewhat higher prices accordingly. But none of these engines have by any stretch approached the "unobtanium" stage!

The beam-mounted .049 and .099 cuin diesels will be found to be highly serviceable units as delivered, requiring no more than ordinary care in operation. The smaller model seems to prefer fuels with a slightly higher ether content than some others and also likes a good helping of ignition improver. But both models start and run OK on any good modern diesel fuel.

The original radial-mounted "Duro-Glo" .049 model requires a more cautious approach. The early examples with the compound induction port in the shaft are notoriously prone to shaft breakage in normal service—Ron Warring's experience was by no means unique. If you plan to use the engine to any extent, it's relatively straightforward (if you know what you're doing) to remove the sharp corners with a suitable Dremel stone, although it's important to avoid altering the timing if you try this.

However, the fragility of these shafts is due in large part to the fact that they were over-hardened at the factory, and this issue can be addressed to some extent by normalizing the shaft. To do this, the shaft should be placed in a cold oven which is then heated to 550 degrees Fahrenheit and held there for 2 hours or so. At the end of this period, the oven should be switched off and allowed to cool slowly over several hours without opening until it is merely warm. Upon removal, the shaft should have a blue tint to it, indicating that it became hot enough to take the edge off the brittleness and relieve internal stresses.

This treatment will not guarantee the integrity of one of these shafts. I have one which I treated in this way which has survived over two hours of hard running, but I'm holding a spare in reserve! The later shafts which have a round induction port with rounded corners and edges appear to be far less prone to breakage in service. Even so, I have always normalized these shafts too, just in case.

Before running one of these engines, I'd recommend that you determine which shaft you have. You can then make an informed decision regarding whether or not to run the engine without further intervention beforehand.

Another decision which needs to be taken is how much you value that lovely red colour on the cylinder jackets. Over a period of use, the colour has a marked tendency to fade under the influence of repeated heat cycles. I've always restricted my extended running activities to engines which have already started down that road, but it's your call.

One issue which is not uncommon with these engines is the need to replace the O-ring seal on the contra-piston. It's necessary to use the correct size as well as make sure that the material is suitable for high temperature applications in a hydrocarbon-rich environment. If you can't find an original spare part, the widely-available, high-temperature Viton® O-rings seem to be about the best. They also work well in OK and FROG diesels using O-ring contra pistons.


It's a real shame that the McCoy diesels weren't marketed in those areas of the world in which the model diesel engine still held sway at the time in question. We hope we've shown that they were second to none in design and production terms, regardless of from where one took one's standards, and their performance speaks for itself. If they had been made readily available in Britain and Europe as well as the far-flung Commonwealth countries around the world, they would almost certainly have become best-sellers and might have remained on the market for much longer. If nothing else, they would undoubtedly have raised the level of respect in which the USA was held as a producer of diesels, as opposed to the glow-plug engines with which that country was universally associated.

In light of these comments, it seems a little strange that McCoy didn't persist with their diesel program. They had hit the ground running with a product that was second to none by the standards of its day and was undoubtedly amenable to further development. So why didn't they continue with diesels and extend the geographic range of their marketing efforts?

The answer must surely be related to the 1955 take-over of the McCoy range by the Testor Corporation. That company had its feet firmly planted in the vast North American marketplace and was presumably disinterested in diesels. The fact that the production of the McCoy diesels seems to have ended during 1955 is unlikely to have been entirely coincidental. It's probable that Testor saw the McCoy diesels as being out of place in the context of the North American marketplace which was their primary concern at the time and simply ended their manufacture without giving a great deal of thought to the wider potential of the designs.

The possibility also exists that falling domestic sales may have contributed to the 1955 decision to revert to glow-plug ignition for the McCoy .049 model and drop the .099 diesel altogether. Talking to old-timers who were active in America during the 1950's, a frequent comment is the fact that the availability of diesel fuel was rather sporadic in the USA at that time. Both OK and McCoy marketed diesel fuels which were tailored to their own designs but worked well enough in the competing models. However, those who were "there" at the time recall that such fuels were often omitted from the order books of many hobby shops and were frequently out of stock. Evidently it took some persistence to secure a reasonably dependable supply of diesel fuel. This can't have done anything to aid the diesel cause in the USA. A number of individuals have recalled giving up on diesels for this reason alone.

Despite this, enough of the engines were produced during their relatively short production lifetime that a sizeable number remain in existence today. Anyone having an interest should be able to find one on eBay or elsewhere without too much trouble and at not-unreasonable cost. And I recommend that anyone with an interest in diesels do so! These are good-looking, finely-made engines that run extremely well and will give excellent service if approached properly. So by all means give one a go!


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