Alan McCulloch's Model Engines

by David Owen and Maris Dislers

Click on images to view larger picture,
hover over the images for a description.
    The McCulloch 5cc Red Special
    The McCulloch 2cc diesel
    Running the McCulloch 2cc diesels
    The Delta 490
    The Delta 490's design
    Running the Delta 490

As in other parts of the world, the short supply of model engines in the years immediately after WW2 led a number of Australian enthusiasts in Adelaide to try their hand at making their own, with perhaps a few for their mates. Jack Black (Jay Bee 60), Harold Clisby (better known as the maker of Clisby air compressors) and Gordon Burford (no introduction needed) all had a go. So did Alan E. (Billy) McCulloch.

Qualifying after the war as a fitter and turner, Alan purchased a new Qualos centre lathe in 1947. Alan was working with his father William Wilson McCulloch, building and maintaining Ferris wheels and other carnival equipment. In his spare time he built his first engines. When visited in 1998 by David Owen, Alan was 71 and quite surprised that anyone would be interested in his model engine endeavours. Unfortunately his recollections were sketchy. It is probable that he began with a 2cc diesel of his own design. We'll cover that one later, but begin with his 5cc diesel.

The McCulloch 5cc Red Special

The Red Special was preceded by an unpainted engine, identical except for the paint and probably marketed by Alan McCulloch himself. He seemed to recall building roughly a dozen of these before becoming associated with Bill Evans.

The Red Special engine (the McCulloch 5cc Diesel painted with red Dulux enamel) was marketed by W.Wilton (Bill) Evans of Model Aircraft Industries (MAI), 3 Percival Street, GLENELG South Australia. MAI's price list dated November 1948 was a small Roneo-printed affair boasting "the most comprehensive range of model materials available in Australia". Stock was available to the trade or by direct mail order. Along with the ED Mk II, FROG 100 and Milford Mite Mk II diesels, MAI listed the ".325 GEE BEE" made by Gordon Burford and Alan MCulloch's " .29 cu inch "RED SPORTS MODEL", both priced at 9/9/-. The McCulloch engine was described as "same as the "Gee Bee" but Class "B", 5cc and overall size has been reduced to facilitate close cowling etc. An ideal motor for Diesel speed models..."

Already "superseded" by the GEE BEE Stuntmota when the first issue of Australian Model Hobbies came out in June 1949, an advertisement in the subsequent September number by MAI stockist Curries Model Aerodrome in West Perth, Western Australia lists it as the "G.B. Red Special 5.c.c." selling at a reduced 8/19/6. The apparent connection with Gordon Burford's engines is incorrect, but this advert in the mass media of the time gave Alan's engine its toe-hold in history and the Red Special name has endured to this day.

The Red Special's design is heavily influenced by Leon Schulman's Drone Gold Crown engine introduced in 1947. The Drone was effectively unobtainable and very desirable to the Australian enthusiast of the day and Alan must surely have had access to an original example. Much of his engine is an outright copy, but Alan did not shy away from adding his own ideas to this American design. The Drone and some of its contemporaries demonstrated that fixed compression diesels could work satisfactorily, but it seems Alan heeded the old engineering axiom stating that if something can't be made perfect, make it adjustable. His engine has variable compression via a compression screw and brass contra piston fitted to the cylinder. Less obvious is the shortening of the conrod and other alterations that allowed a reduction of engine height. This aspect was specifically mentioned in the 1948 MAI catalogue. The Red Special is 88mm tall and weighs 251g, compared with the Gold Crown Drone's 99mm and 270g (with tank).

The Red Special varies in other details that necessitate a degree of individual attention not possible in mass production. For example, the backplate has an internal step to clear the piston at the bottom of its stroke. A corresponding bulge is cast into its outer profile. The backplate threads into the crankcase and must therefore align quite closely to a specific position when tightened. Presumably Alan individually made adjustments during machining of each engine to ensure the parts aligned correctly.

In terms of performance, reference should be made to Adrian Duncan's report of the original Drone engine. There is no reason why the Red Special would have been any worse. In fact our experience with the variable compression Gee Bee Stuntmota of similar specification suggests that the McCulloch engine would have had a broader operating speed range and would have gained a boost of around 10% more power from the nitrated fuel, which was not available to its progenitor.

Alan recalled a modest production run of approximately 60 engines. Anecdotally, painting them red was Bill Evans' idea for adding market appeal. Ferrari has done the same with their motor cars to this very day. However, not all of Alan's engines got that "treatment". The accompanying photo shows an engine with only the main crankcase painted, while others are known to have the upper crankcase casting painted up to the lowest cylinder cooling fin. Heads and backplates are thought to have been left unpainted.

The McCulloch 2cc diesel

Thanks go to Mal Sharpe for bringing to David's attention the almost forgotten McCulloch 2cc diesel. Its relatively simple design suggest that it was Alan's first go at making engines and may have materialised (at least in its initial form) soon after the Qualos was put to work in the McCulloch workshop.

This engine has a relatively simple and compact design, achieved by having front rotary induction and fuel carried in the rear crankcase cavity/radial mount. A commendably low weight of 113g (4 ounces) is a full third lighter than the contemporary and widely used ED Mk II. It has a bore of 13.06mm and stroke of 15.70mm, giving it an actual capacity of 2.10cc. The neat sand-cast aluminium crankcase, incorporating a radial mounting flange, carries a honed cast iron bush for the hardened steel crankshaft. This component has a hefty 8.5mm journal and 3/16in. crankpin. The intake opens 50 degrees ABDC & closes around 25 degrees ATDC, giving intake duration of 145 degrees. Design-wise, McCulloch knew what he was doing!

Three 3/32in. BSW machine screws retain the hardened steel cylinder, which has two opposed exhausts and a single transfer port, fed from a milled passage in the front of the case. All ports are broached precisely rectangular. We measured exhaust duration at 125 degrees and transfer at 110 degrees. The flat-crowned cast iron piston carries a sensibly proportioned, machined aluminium conrod on a brass piston-pin.

Allan also used brass for the single-lever compression screw and red brass or bronze for the contra-piston. Like the Red Special, this engine shows the hallmark of a very competent engineer, being very nicely finished and fitted.

A second, incomplete McCulloch 2cc diesel emerged from the shed of Brian Horrocks, well known for his Control Line aerobatics achievements. It comprised the crankcase and piston/cylinder/conrod assembly, and is of interest because these components differ significantly from the other engine. All the more reason to rebuild the incomplete engine (we'll call it the Type 2) to running condition, using the complete (Type 1) engine as a reference.

Clearly a major redesign had occurred; perhaps quite some time after the earlier engine was made. Type 2's porting is of the cross-flow type, suggesting that this engine was not made until Allan had examined and incorporated this feature from a Drone Gold Crown engine. A chamfered lower cylinder edge eases gas flow through the transfer port before it is directed further upwards by a baffle notch cut into the hardened steel piston crown. A single exhaust port is on the opposite side of the cylinder. Two channels milled into the crankcase allow unobstructed conrod travel. One also performs the transfer function, as the other is closed at the top by the cylinder mounting flange located just below the exhaust port. Allan obviously took pains to get the port dimensions to his liking. Additional work with a fly cutter raised the top of the transfer and lowered the bottom of the exhaust port. Simply locating the transfer port below the cylinder flange and the exhaust above would not do.

Logic dictates that with more thread on Type 2's upper cylinder, a longer cylinder jacket was intended and the extra thread length equates to one more cooling fin than the Type 1. The Type 2 engine is around 3mm shorter than its partner owing to a shorter conrod and higher gudgeon pin hole in its piston, accentuated perhaps in the side by side photo by its lower cylinder flange location. Perhaps this engine was the guinea-pig for the same revision of the Drone design formula as it morphed into the Red Special.

The Type 2 engine's crankcase extends further behind the cylinder, possibly to increase its on-board fuel capacity. Engine mounting is via three holes in the rear crankcase flange at 120 degree spacing. These holes were curiously small on Type 2. There is no indication how Allan sealed the fuel cavity. The simplest set-up would be direct mounting onto the model's firewall, perhaps with a paper gasket to stop leaks. The final difference is crankcase finish. Type 1 is left as cast while Type 2's crankcase had been extensively fettled before receiving its coat of red Dulux.

Running the McCulloch 2cc diesels

Type 1 was an easy starter and ran smoothly throughout its useable speed range. There was no need to adjust compression setting for starting, which is just as well. The brass contra piston (a tight fit even when cold) soon jammed in the cylinder as the assembly reached running temperature. Frustrating when zeroing in on peak RPM readings, but generally the engine was quite accepting of compression settings "somewhere around the mark". Response to mixture adjustment was predictable and comfortably made thanks to the swept back spraybar location and large needle body.

The engine's power output of 0.085 BHP between 6100 and 7700 RPM only just matches the Mk 2 Mills 1.3 and was down on expectations. Most probably, this McCulloch, like so many of its contemporaries that have survived the years has lost its optimum piston/cylinder fit after a long and useful life. On paper at least, it ought to match an ED Comp. Special for horsepower.

Type 2's piston and cylinder showed no such problems. Initial runs with classic un-nitrated equal-part fuel gave somewhat unsteady running and power output little better than the Type 1 engine. Switching to nitrated fuel did the trick, showing the superior cross-flow scavenging to maximum advantage. The resulting torque curve tops 18 ounce-inches at around 7500 RPM and BHP touches its peak of 0.145 somewhere between 8000 and 8500 RPM. While it is likely the Type2 McCulloch cylinder porting and rotary induction have the potential for even better performance, vibration at speeds over 9000 RPM applies the brakes quite emphatically. That lovely needle reaches a harmonic vibration, winding out despite the best efforts of the strip brass ratchet. We did not explore whether it could leave the vibration zone behind and operate effectively at higher speeds.

The McCulloch will run for two minutes on its on-board fuel supply, which is much longer than is prudent for free flight work. More likely, it was intended to fly control line models. In that application, its power to weight performance easily tops the then commercially available alternatives. So why did this promising design offering 30% more power than the ED Mk2 at a lighter weight only lead to no more than a dozen examples being made? The answer may well be a "Flash News" announcement in the June 1949 Australian Model Hobbies magazine. MAI were expecting delivery of the "up-to-the-minute" 2cc Hawk/Falcon and 5cc Vulture MK II and Mk III diesels from "K" Model Engineering of Kent. Alan's engines, handmade as a side-line, were unlikely to match these widely advertised, quantity-produced alternatives.

The Delta 490

Always the energetic entrepreneur, Bill Evans had expended his business to also include a retail store, a spot on local radio and sales of his modelling magazine were booming. Next up was to increase model kit production under the Aristocrat brand and enter model engine production. The "New Motor Preview" in the Spring Issue 1952 of Australian Model Hobbies announced MAI's new 5cc glowplug engine thus;

"The Delta 490, the latest motor to appear on the Australian market, was designed by Bill Evans—editor of Model Hobbies—and developed in conjunction with Alan McCulloch, who has been responsible for several motors produced in Australia, such as the Gee Bee Red Special, and various parts of most Gee Bee motors. This has given him some considerable experience in model motor design and production, which coupled with his experience in the engineering field meant a lot of "know how" could be put into the "Delta" so as to produce a hot motor at a competitively low price".

More likely Bill conceived and sketched out the general concept of a high-end engine clear of the popular Frog 500 in the marketplace, but more affordable than the ETA 29. In all probability, Alan more-or-less attended to the detail engineering aspects, prototyping and tooling up for production. His involvement with quantity production is believed to have been minimal.

Coincidentally, Australia's balance of trade had plummeted to a massive 21% deficit in fiscal 1951-52, prompting the government to introduce immediate and severe restrictions on imports. Quotas were introduced and modelling goods were suddenly in short supply. It was very tough on the trade and the situation led to Monty Tyrell leaving Hearns Hobbies in Melbourne and taking a position in Adelaide with MAI. This was late in 1952 when the Delta had just been announced, but was not yet on the market. Here is his first-hand account.

"When I hit the Model Aircraft Industries set up, my being there enabled Bill Evans to have more free time to get the engine manufacturing division started. He rented a factory in North Unley and along with George Nixon and Royce Ryan got the Delta 490 into production. In between running the shop in Franklin Street (Australian Hobby Centre) and packing kits in Model Aircraft Industries' factory, I used to spend the eighth day of the week hand testing the Delta production run as I felt a sport motor that couldn't be hand started was a useless object.

The knock back rate was high but I'll die happy knowing that most Deltas which got out into the market would actually run.

The Delta was nothing but an import cuts special which enabled many to keep or start flying. It sold for eight quid ($16) which was about 60% of the weekly pay."

The Delta 490's Design

Inspiration probably came from the 1951 AMCO 3.5BB designed by EC (Ted) Martin. It was a standout performer, yet displayed a wide useful operating range and was easy to handle. The Delta follows the same general arrangement. Beyond that, the Delta is of course a glowplug engine and of greater swept volume. The specification (printed along with the operating instructions on the bottom of the box) is as follows;

"Bore 18.5mm Stroke 18mm. Capacity 4.836cc. Weight 7 ounces. Compression ratio 9.5:1. Mounting beam. Recommended airscrew F/F 10x6, Stunt 9x6, Speed 7x9, T/S 9x7. Cylinder S14 hardened, ground, honed, liner. Porting Exhaust four ports, Bypass eight 14" channels. Crankcase/cylinder, casting hydinium. Head held by six screws. Piston conical deflector, no gudgeon, ball joint fitting. Connecting rod Steel, brass bushing. Crankshaft nickel chrome. Crankshaft bearing Two ball races on racing model, Cast iron on standard model. Induction valve rotary disc. Special features Downdraft carburettor. Long mounting lugs. Starting very good using standard fuel. Necessary to keep head gaskets in good condition as motor proves tricky if gasket is compressed too far, increasing compression."

There were no factory designations between the different models, so to clarify the distinctions, we'll call the original model Mark 1.The Delta 490 design underwent two major revisions during its production run of around three years. The market may have seen these revised models concurrently; a revised rear induction model with lingering racing pretentions (we'll call it the Mark 2) and a derivative front induction model (the Mark 3) that was better suited to general purpose and stunt work.

The original design was thoroughly revised inside and out. The Mark 2's new finned, cylinder head is held down by four (not six) screws and is typically painted a burgundy red colour. The crankcase has an additional lug giving three-point mounting for a new "back door" casting. This has a flared venturi profile and gentler curved transition to the intake window. Internally, the new model has a cast iron piston with pressed-in gudgeon pin and cast aluminium connecting rod. Four of the eight transfer flutes have been omitted from the cylinder. An aluminium prop driver screws onto the crankshaft threads, rather than the previous steel driver engaging a square shaft portion. The tendency of this set-up to coming loose from a back-fire was later overcome was eventually overcome by having a redesigned prop driver with a generous spigot locked against a tapered split collet that screws onto the crankshaft threads.

We've yet to see a plain bearing Mark 2 engine. More likely, that demand was better met by the Mark 3 version. This shared the Mk 2's piston/cylinder arrangement, but the crankcase die was again irrevocably modified for a front induction format. All Mk 3's were of course of the plain bearing type, as there is inadequate provision for a large enough rear ball race for an FI crankshaft. Crankshaft diameter was upped to 7/16in. (11.1mm) versus the solid Mk 1 and Mk 2 crankshaft's 5/16" (7.95mm) journal diameter. Mk3's stroke was marginally increased from 18 to 18.5mm, giving a nominal swept volume of 4.97cc. Keen eyes will spot that the lower backplate mounting lug was made more substantial toward the very end of production. Minor changes in small part design (e.g. needle valves, prop drivers/washers) consistent with small batch production methods have been noted. This is summarised in the table below.

TypeHeadRear coverCylinder piston assemblyProp driverCrankcase Weight
Mk 1
Rear induction
BB and PB
No fins, six bolts, as machined finish.Two-bolt mount, straight-sided carburettor tubeEight transfers, ball-joint piston, steel connecting rodSteelAs cast, threaded for two rear cover retaining screwsBB 234g
PB 221g
Mk 2
Rear induction BB only.
Assume PB variant not made.
Finned, four bolts, red paint.Three-bolt mount, flared carburettor opening.Four transfers, gudgeon pin, cast aluminium connecting rodAluminium threaded (early). Aluminium with collet (late)As cast (early). Sand blasted (late). Through-drilled for rear cover screws/nuts240g (8.5 oz)
Mk 3
Front induction
PB only
As Mk 2 RV, but as-cast finish (early) or black anodised (late)Backplate with flat indent (early). Double-step indent (late)As Mk 2 RVAluminium threaded (early). Aluminium with collet (late)As cast (early). Sand blasted (late) Through-drilled for rear cover screws/nuts204g (7.1 oz) Early 213g (7.5 oz) Late

Running the Delta 490

We chose a late model Mk 3 engine for testing. Initial runs were awful, owing to a poor piston/cylinder fit. In the course of the rebore, the cylinder bore was found to be significantly out of round and with a nasty bell-mouth at the top suggestive of poor honing practice. This was trued up reasonably well and a fresh piston was made and fitted.

The rebored engine started easily, providing the exhaust was primed. It tended to run flat out. Richening the mixture from peak had little effect on engine speed. Even winding the thimble off the spraybar and drawing the needle out to give maximum flow failed to get the classic four-cycle run so in favor for stunt work these days. It appears that the effective choke area of over 15 sq. mm is over-optimistic for this engine and a figure around 8-9 would make it far more tractable with little loss in useable performance.

Running was steady with the 5% nitro fuel used, giving our first test reading of 10,900 RPM with APC 10x4 propeller. Then the crankshaft failed for no apparent reason—broken straight through the journal at the widest point of the round valve port opening. This was unexpected, given the generous wall thickness of 1/16in. (1.6mm) in this area. Perhaps this particular crankshaft had been abused by the previous owner, or unsympathetic case hardening had left it in a brittle state, as shaft breakages have not been a reported defect of the marque. In any event nobody else wanted to submit their Delta to a full performance testing program. Instead, we've assembled some previous spot test figures from several other engines.

When pondering these performance figures, it might be useful to keep the following data in mind. Checked exhaust duration is 140-146 degrees and around 90 degrees transfer duration for all Marks. The Mk 1&2 intake opens very late at 80 degrees ABDC and closes 60 degrees ATDC. The Mk 3's intake is more conventional opening at 60 degrees ABDC and closing at 55 degrees ATDC.

EnginePropellerRPMApproximate BHP
Mk 1 BBAPC 10x48,8000.19
Mk 2 BBAPC 10x410,2000.30
APC 10x58,8000.22
FI (early)APC 10x410,3000.31
Taipan 10x69,2000.29
FI (late—rebored)APC 10x410,9000.37

Clearly there are significant differences between individual engine outputs on the same propeller load. This is probably more influenced by piston/cylinder fit (which seems to be universally on the loose side) than anything else. Fit and finish of other components seems to be quite adequate. The somewhat better result from the rebored engine hints at what might have been if Allan McCulloch's high standards of internal fit and finish had been achieved by the manufacturer. Furthermore, it seems that the added complexity and weight inherent in the Mk 1 & 2 models did not pay off in terms of performance.


Monty Tyrell observed that most of the 490's were of the ball bearing type. Going by the number of survivors, we'd say they were mainly Mk 1's bought at the time of shortages. The balance of payments swung back to a healthy surplus of 26% in 1952-53 and import restrictions subsequently eased.

Despite the considerable efforts to bring out the Mk 2 and Mk 3 models, the Delta's reputation as noisy and gutless did not change. All hope of producing a wider range of engines from 1.5cc to 10cc (foreshadowed in the 1952 advertisement in the unofficial Rules Book for Australia by Allan King and Monty Tyrell) Deltas dropped from the scene after a total production run of around two or three hundred units.

For whatever reason, Alan McCulloch ceased all involvement with model engines at the very early stages of the Delta program.

Those with a positive outlook might say that with a bit more time to develop the design and get the quality problems sorted, the Delta would have made a good engine. People who paid quite a hefty sum for one, only to be underwhelmed by its performance, would be less conciliatory and it is believed that the backers who put up the capital for the engine manufacturing machinery lost heavily from the venture.

Our thanks go to Mal Sharpe, Peter Lloyd, Don Howie and Anthony Williams for their assistance with this report.