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how do i see my squosh rateing on my b1 engine

1176 Views 3 Replies 4 Participants Last post by  nesikachad
hello so i wont to find out what my squosh rating is can i use whats in the pic if so how if not what do i do? and i wont to do it on my b1 engine and also my polini reverse as well and is there anything with the b1 engines i should know about as im only really good with the polini now but im willing to lern


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I do it with the head piece off. If the piston is not right at the top of where the cylinder ends at TDC, you have to much space. The pistons have a crown and usually hit about 3/8" in from the outer edge. If the edge of the piston has .050" left before the top of the cyld, thats way to much space. You can put masking top in the head or on top the piston to see if its hitting when you get real close. If you try to mill the cylinder down you lose your o ring grooves. A thinner base gasket is the way to make the piston go higher. On my Polini there is no water going from the cases up thru the cylinder, but on a B1 got to have a good seal, so water don't leak at the base, don't know if Yamabond with no base gasket will probably work, its rubbery and seals pretty good.
With the head assembled you take 3/32" electricians solder give it an L shape,,put it through cylinder hole,,crank engine to squish solder,,,after squishing you pull it out and measure the squished part with a caliper/micrometer

The squish on my stock modded 1pc head engine is around .028-.029" after adjustment and basegasket loss..Stock was 1.05mm's...LOL

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Racing giant scale RC planes (240mph sometimes) on methanol and nitromethane has taught me some stuff with 2 cycle engines.

1. Quench rings want to be at 10% of the bore dia. for best power.
2. Quench ring angle is important. I have best luck with a 1/2 degree.
3. The transition to the chamber is also important. A generous radius seems to help with top end power. A sharp/crisp transition helps with throttle response on small bore engines.
4. Lowering the jug does raise compression, but it also alters the port timing. Don't forget about that as its important.
5. If you want more top end, increase the exhaust timing. It'll make the engine "peeky" though.
6. Compression with gasoline and H2O cooling is your friend. The more the merrier. It makes EVERYTHING work better. Just know that your fuel quality has to be good and with crazy CR's it means $12/gallon race gas. My Phantom is 17.5:1CR and it looooovvvvvveeeeesssss VP Q16 gasoline.
7. Oil: I like an oil that has castor in it. Yes it varnishes, but I've never had a ring stick. Can't be said for pure synthetics. Just sayin based on personal experience with air cooled 220cc twin cylinder 2S engines buzzing along at 12K and consuming 125+ fluid oz of methanol/30% nitromethane per minute. Nevermind the 25+G's developed during cornering. Thirsty buggers!

Figures as I pay almost $14/gallon for it.

Good luck.
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