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a very small 4 stroke engine : 1.35cm3

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I present you my last engine almost finished and running; a mini 4T of 1.35cm3, (0.08cu in) (bore and stroke: 12mm).,
I wanted a 4 stroke engine, spark ignition, with a reasonable noise level, good power and not running too fast. The goal was to get an engine capable of moving a small mechanical diesel shunter for the 45mm,  gauge 1 track at 1/32 scale more precisely.
So I designed a model inspired by some early engines with a camshaft parallel to the cylinder driven by helical gears, with also a low compression ratio, about 4.3; the cylinder head having a large combustion chamber with face to face valves, quite in the style of the Wyvern and Centaur from ET Westbury, from which I also copied the rocker arm style. The cylinder head has 2 valves controlled by rocker, but I reserve the option to test an automatic intake valve if all goes well.
I also put a water tank for cooling, rather than a water jacket and its associated pump, radiator and fan owing to limited space.
There is also a large flywheel (relatively!) for the smoothness of operation for such a small engine, leaving me the possibility to put a second one on the future drive side.
There is for the moment a traditional ignition with breaker and HT coil; I  had to make some home made spark plugs, mini too, the 1/4 x32 being too bulky on this tiny cylinder head, especially with the carburettor too close to the spark plug, not easy to adjust air intake without receiving electric shocks!
After a rather long running-in, mostly because of my "shop-made" helical gears, it has no more stiffness and started easily, responds well to settings for air, fuel and ignition timing, and runs like a clockwork, but alas, far too fast for my taste, between 2500 and 5500 rpm, the noise being not the expected "put-put-put", but in an acceptable range.
Ií m actually doing an electronic ignition and rebuilding a more advanced carburettor than the simple mixer, and do some power tests to see if the rest of the program is feasible.
but I'm currently making an electronic ignition from a gas lighter as shown in the Jan Ridders website.
Iím also drafting a final version of my plans, but Iím not expert in this field !
I will post some pictures of the building of my engine, after the final result, I agree that this is not the usual way to proceed, but I have to select lot of pictures in my computerÖ

Roger B:
Excellent  :praise2:  :praise2: Fitting a spark plug and valves into a 12mm bore is not easy. Did you use piston rings?

Congratulations Zephyrin on a great runner.  It is a really neat and compact design.


Hi Francois, very nice.
I should put something similar on my retirement list.

That is fabulous! Thank you for sharing here.


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