The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => A7 & A10 Engine => Topic started by: melvyndalby on 26.08. 2011 19:47
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I recently aquired a BSA Rocket Goldstar (REP), it has +60 pistons in it, can anyone tell me how I can find out the compression ratio, thanks Mel
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With possible exceptions, flat top 7.5:1 , raised portion and then flat top 8.5:1 , Domed top 9.?:1
Could differ depending on make I would think
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Really tall peaked top, 10:1 (oooh, very scary, batten down the hatches, wear the brace on your rightright. knee).
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G'day Mel, welcome to the forum.
Also look inside the piston for make or casting #'s then google.
The other way is a bit messy, but the one I use, is to cc the combustion chamber. With the piston on TDC comp stroke lean bike over till the spark plug hole is vertical, then using a syringe accurately measure how much oil it takes to reach the bottom of the spark plug thread. I do this to make sure both cylinders are the same. Swept vol of cyl + your cc / your cc = comp.
Cheers
Just saw manosound's. I got 10.5:1 in the cafe, but I'm still a month away from 50. *smile*