Office of Steam Forum for Model & Toy Steam Gas & Hot Air Engines

I Did see Gil's slow-motion video and I think that is a Great test to actually count revolutions between hits...this is probably the truest test of friction reduction and also how your other settings are working, for example: timing settings.
   I have not took the time to try to calculate the compression ratio by actually measuring the swept Volume or the area that's left when piston is at top dead center....I do not place a lot of trust in the China instructions asking for high octane fuel as a gauge for compression ratio...many have run there engines on 87 but the engine does have what I would describe as snappy compression stock...I have reduced my compression perhaps 70% of max can be achieved by milling piston top and also the material I removed from the head. If I took the dish out of piston and made it flat with perhaps only .050 thickness left on piston top I would be at max reduction from shaving piston....I wish they offered spare pistons as purchase parts so I could get a little Wild with my experimental tests...another thought would be to leave the piston top stock and ream a new wrist pin hole closer to the top which would have the effect of moving the piston further back in the bore by quite a bit....next time I have my piston out I will take some measurements to see if this is possible...likely have to trim a bit from the skirt as the piston may travel to far rearward. I have the ability to make a new piston from scratch of my own design, however finding time is another matter.