The Clanford "Clan"

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The Clanford Clan was a sub-miniature compression ignition engine manufactured briefly in England, circa 1976, under the direction of Mike Clanford, he of "A-Z" fame. It was a tiny side-port design featuring a barstock crankcase with a plastic injection moulded tanktop/venturi assembly, and as you can see, came in a variety of colors. Tiny diesels are tricky beasts, both to make and to operate. With the Clan, this latter aspect was compounded by an occasional manufacturing defect which prevented transfer, so if you had one and could not get it to run, it may not have been your fault!

However, as it appeared to possess an elegant if deceptive simplicity, we drew a set of Motor Boys Plans for it way back in the dying days of the last century. What with one thing and another, none of The Boys ever got around to building one from the plan. But a few plan sets have been sold and I'm absolutely tickled pink that MEN Member, Mark Lester, (whose work has appeared here before) has completed a running example. I asked Mark if he'd share some notes on the experience with us. The remainder of this page describes his trials, tribulations, and recommendations.

Ron Chernich, Brisbane, August 2009


Building the 0.24cc Clanford Clan

by Mark Lester


My Clanford Clan 0.24cc was made from the MBI plans, assisted by hints and techniques from the MEN web site and advice from other experts. The process took about three years and came near to being abandoned after having lapped about four cylinders and five pistons and still getting nowhere. Then I saw an article in Sam Speaks (SAM 35 newsletter) which featured a 0.25cc diesel by our very own engine maestro, Normal Fallowes. So I gave him a call and he generously sent me a few tips which helped me complete a decent cylinder/piston combo. I'm pleased to pass on the experience and hope these notes help others building this, or other small diesels.

Like many engine builders, I deviated from the plans in a few small areas, namely:

ed: The following notes on the parts describe how Mark went about the tasks. To save you hunting around, I've added hyperlinks to the processes he mentions as having found useful.

Crankcase: fabricated from round bar aluminium stock as per Weaver instructions. The photos above show some of the machining operations and the end result. It would probably have been a lot easier to have started with a cube, turned in the four-jaw.

Piston: machined from Meehanite cast-iron. Internal con rod clearance milled with assistance of an Optical Centring Microscope built from a kit supplied by Hemingway Kits (UK). The Gudgeon pin is an interference fit one side of piston and tapped home with a light hammer and drift.

Contra piston: constructed using the DCO method per the MEN "How To" article.

Con Rod: fabricated from alloy front bicycle sprocket, in the usual way—for me! On trial assembly, con-rod clearance proved to be somewhat lacking. To achieve clearance, easing was required; the con-rod, the crankcase and the base of the cylinder on both sides. One has to be careful here to preserve the "knife edge" seal of the cylinder against the crankcase.

Needle: two were constructed, both brass. Both had bonded needles inserts to engage jet. One needle was made from 1.0mm hardened silver steel. The other 1.0mm piano wire. The tapers both ground freehand in both cases using two Mini Craft hand-pieces, rotating the wire against the rotating cut off disk (see photo). Both hardened silver steel and piano wire appear equally effective. Although not probably as accurate as the MEN "How To" article, this method keeps the grindings away from the lathe bed and seems to work for me. By the way, please use protective goggles when using a cut-off disk.

Prop Driver: a simple knurling operation as per MEN "How to Do" write up.

Fuel: I used Southern Modelcraft Sport Mix, a can I have taken back and forward to the flying field for about three years! (I don't use much). It says 30% ether, on the tin. No additional ether was required, but I always seal the cap tightly when not in use.

Laps: Steel laps were used for both cylinder and piston. The cylinder was lapped with Timesaver lapping compound, suggested by Ken Croft. I use Solvol Autosol to lap the piston and contra and to finish the cylinder bore. A problem that I perceive with an internal split lap is that the hacksaw split tends to "petal" the sides apart. This produces a lap that is too tapered, in my opinion. I managed to alleviate this by inserting a fractured hacksaw blade at the base of the cut and then squeezing the sides together in the vice. This achieved a much more parallel lap. You can just see this in the photo of the lap.

I fell into the trap of producing an over-tapered bore (and over tapered piston). I now believe that parallelism is critical with these small bores and the very useful tip which Norman Fallowes gave me was to make up a double ended bore guage. This is made from steel rod with turned and lapped brass cylinders to match the bore diameter, but one end was finished at 6.5mm diameter (nominal bore diameter for Clan) and the other end I finished at 30 microns smaller diameter. After producing about four duff cylinders, this tool enabled me to recognise whether I was producing a parallel bore, at last, but with an absolute smidget of flare below the exhaust ports (sorry for the unscientific terminology!)

This was not quite the end of the story because piston number 5, which I made to match my perfect cylinder, still did not produce the necessary compression. I concluded that I had overdone the taper of that! To prevent this happening again I took the precaution of making a new piston and a new piston lap but before lapping the piston I ran the internal and external laps together with lapping paste. This achieved a piston lap with a very smooth and parallel bore in order to produce a satisfactory piston fit.

For external machining and lapping of the piston, a fixture like the one shown here is required. Also shown are a reject piston which can be clearly seen to be undersize at the top end ie excessively tapered, which is bad. The basic design of the piston holding tool is copied from Richard Gordon's article on Alpha (a more universal fixture developed from this idea was featured as the MEN Tech Tip for July, 2007). Note that the piston holding tool has two shoulders, the first of which sits under and stabilises the piston when the gudgeon pin (not illustrated) is passed through the piston and eyelet, then tightened up.

Also shown is a reject cylinder. Please note that there is a second shoulder which coincides with the base of the cylinder and the diameter is fractionally smaller than the required cylinder bore. The first piston that I made was a replacement for an Albon Dart and I proudly lapped away until the piston was of a diameter that it popped right through the top of the bore. This I soon found to be a mistake which produced poor compression and gas leakage because, as I have indicated, the cylinder bore is slightly wider at the case of the cylinder compared with the top. I have thus arranged the machining dimensions of the second shoulder to coincide exactly with the position of the piston at TDC, thus ensuring a tight piston fit in the bore. That is how I now make all my piston holding tools You may be interested to note the left hand end of the piston holder is for the 5mm piston of "Nano" and the two shoulders are designed with dimensions based on the same measurement principles.

I always use tallow for trial fitting of the piston in the cylinder bore as considerable force is required to work the piston up the cylinder and the tallow helps to prevent locking up. The red mark on the piston is felt tip that I always apply when assembling or dissembling and engine. The mark is applied to the front surface of the piston, the con-rod and the gudgeon pin and I always arrange to pass the gudgeon pin through the assembled piston and con-rod from front to rear. I'm not sure whether this is industry standard, but it helps me to get the parts the right way round!

Other Tools Used: Myford Diamond 10 lathe with vertical slide and one or two accessories that broadly follow the design parameters of Heath Robinson! ER collet set and chuck are invaluable. HSS toolbits were used mainly and the small ones (internal and external threads, etc.) shaped and sharpened with the cut off disk, freehand. I do use titanium carbide tipped tools for final cuts where a very fine finish is required.

In summary, I would make the following recommendations to a novice attempting the Clan, or other small compression ignition engine:

  1. Make up a bore gauge as described above before attempting to lap the cylinder.
  2. Aim for a parallel bore and piston but flare the bore below exhaust ports only a minute amount.
  3. Use tallow when trial fitting the lapped piston in the bore.
  4. Read Richard Gordon's articles on the 0.5cc Alpha and 0.1cc Nano engines (also read the "How To..." articles on the MEN web site).
  5. Don't worry about high ether fuel for this engine.
  6. Keep asking the experts for advice—they are all very helpful

The finished Clan has proved to be a pleasing engine. Building it taught me a lot and I hope you can gain some benefit from my experiences. Now I just have the challenge of making up a suitable airframe!