Hi
I have this bsa a65 and need to know what a compression should be , at the moment I'm getting 100psi, any ideas?
I've never been convinced that you can properly measure compression in a kickstart engine. A reading of 100 psi is a bit low and, depending on which A65 this is, a minimum closer to 150 psi would be expected in an accurate measurement.
Yes I was thinking it a bit low, thanks
Variables to consider when doing a compression test,
Hot or cold engine?
compression of the pistons fitted? 100-120 isn't too bad for a low compression piston, 140+ for a high compression.
Camshaft fitted? Race cams have a lower static compression than an A50 (early A65) cam for example.
Throttle fully open or closed?
When testing it should be on a recently ran engine with the throttle fully open. 2nd kick is usually higher than the first also.
If your still getting low values, put a drop of oil in the cylinder and try again and see if the values increase. IF it improves like this then consider a re-bore or a hone with new rings... If the engine is a recent build, get another 500 miles on it then check it again.
Thanks
The engine is not being run as I'm going to retire it but just wanted to see if I need to rebore it , throttle slides were open /engine cold.
Not sure what piston are in . Bike is 1971 so assume it's 9:1