Hello.
A miniature two stroke triple! A great idea, and one of the many projects I have planned to do but still haven't managed to make a start on.
During my motorcycling years throughout the 1980's I used to ride a Kawasaki KH 250 triple. A wonderful bike with an engine that is a work of art, the crank runs on no less than six main bearings. My last bike in 1992 was a big Suzuki GT 750 water cooled two stroke triple, another fabulous Japanese machine.
I do have a liking for three cylinder engines, but not wanting to ride bikes anymore I planned a model three cylinder engine to recapture their distinct sound and feel. Also planned was a four stroke parallel twin and a four stroke triple to represent the three Triumph Bonnevilles and Triumph Trident I once had, where did they all go?
As you suggest, no castings, I planned to use solid aluminium bar for the crank cases, probably square bar. Also aluminium cylinders with cast iron liners and spark ignition to run it on petrol.
It was going to be a relatively large model with a 30mm bore and stroke, making it around 63cc in total. I bought some small needle roller bearings for the big ends, to experiment with.
With a pressed up crank I was thinking of trying metal labyrinth type inner seals as used on some Yamaha engines, but with normal rubber garter type seals on the crank ends. I could not decide whether to use six ball race main bearings, as on the Kawasaki you mention, or just four as used on the Suzuki triples.
I found a company that sells small CDI ignition kits for model engines, and they list one for a three cylinder engine, if it is to be run on petrol.
The KH 250 engine is unusual for a Japanese machine in that it is a long stroke engine, I think it used the same crank as fitted to the 350 & 400 engines so much smaller cylinder bores were used to get the capacity down to 250cc.
A guy I used to work for over thirty years ago used to drive an East German Wartberge car. This had a water cooled three cylinder two stroke engine, I think of about 1000cc. It would easily pull away from a standstill in the higher gears, but it did not have any form of autolube, you still had to mix the oil with the petrol. It did have that distinct sound of a two stroke triple though.
Do you plan to make a water cooled engine? I was planning an air cooled engine as I like the purposeful look of all those fins.
