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I built this engine last year. Modifying the plugs was a lot more straightforward than I imagined it might be. At this scale, seating the valves directly in the heads is not a problem. The forces are very small and the biggest issue with heat is keeping it in, rather than moving it away. I did...

The BSA Bantam started life as the German DKW. After ww2, the design was given to BSA. This may go some way to explaining the mixture of threads. I have a Bantam, a D1 model from 1951. There are no metric threads on it. The engine uses Whitworth plus a few specials, while the cycle parts use...

I have made copper manifolds by plating on to 3D printed formers. They are approximately 0.8mm thick and fitted to my flat twin sidevalve engine, which will be fitted to a flying model. My design has the manifolds well protected from damage.

It is theoretically possible to create high compression ratios with the sidevalve (flathead) layout, but to do so involves compromises on other factors. With the sidevalve layout, the gas flow through the valves is severely restricted. There is virtually no flow at all through the side of the...

No idea of the origin, but it seems to run very smoothly with virtually no flywheel.

Hi Petertha, The material is indeed 316L. The liners were made from short sections of the same tube. I cut a section out of the liner ring, so it could be closed up to fit in the tube. Before cutting the section out, I put each liner ring up in the lathe and chamfered the ID at each end to...

These were 32mm diameter with 1mm wall thickness. I have welded tubes using the same method down to 8mm diameter with 0.6mm wall. The 8mm tubes were no more difficult than the larger sizes, requiring only a few test welds to get the current right. I am using an RTech 160 amp hobby rig, which has...

I have had success TIG welding thin wall stainless tube, by making a 'liner' at each joint. The liner is a short section of the same tube, with a segment cut out so its diameter can be closed up to a tight fit in the tubes to be welded. The use of such liners allows the exhaust sections to be...

Hello Bernd and welcome! My German is not good, but my wife is very German...

All the engines shown are described as "uneven firing". Presumably a 180 degree crank in the parallel twin.

There is another reason for using an iron liner in an alloy cylinder - that is the thermal properties of the alloy, which conducts heat significantly better than iron. This may not matter if you only intend to run the engine for relatively short periods and without load. If you are happy with...

That is impressive, Steve. What gap do you use on those plugs, and do you use "normal" HT system, or lower voltage with longer duration? Thanks for posting.

Thanks Basil, I haven't calculated the compression ratio, just built to drawings. About 6:1 is normal for glow ignition. I'll be using 12% nitromethane in methanol with synthetic 2 stroke oil.

Hi Peter and welcome to the group. I'm also a steam and motorcycle enthusiast. I volunteer at Forncett Industrial Steam Museum and I have a modern Triumph, a 1953 Triumph and a 1953 Panther. If I can offer any advice, it would be to push your limits with every project. I deliberately choose...

I have heard of a few examples of very small spark plugs, but they are indeed the exception rather than the norm and I can only congratulate you on making them work. Since it is my intention to fly my engine in an RC model, I prefer to keep things simple and light.

There is a practical limit to the minimum size of spark plugs. To create a spark hot enough for ignition under compression requires a certain minimum voltage, which in turn requires a minimum thickness of insulator in the plug. About 1/4" is the minimum practical diameter for a spark plug. All I...

This is my collet tool, made from an M8 cap head screw. The hex is bored out to fit the plug, chamfered on the back and split 4 ways with a junior hacksaw. A collar with an internal chamfer is pulled up onto the screw with an M8 nut, closing the collet onto the plug. Also shown is a plug with...

One of the features of this engine is the modified glow plugs. The small size of the combustion chambers does not allow for both valves and a plug. The heads have 3/16 x 40 holes drilled and tapped so that the drilling intersects the combustion chamber. This is visible in the second image in...

The engine is stripped down for final assembly with appropriate loctites and sealant (Blue Hylomar). There are a lot of tiny parts!