In my book 135 is good, nearly great. Where did you get 200 from? That seems a big number for compression to me, but I've only tested old bikes I'm restoring I guess.

 

Read it up on another forum mate won’t mention it but he had a beta 300 with a rk head and he was reading 205 and 155 with stock

 

Are you using a compression tester adapter that's the same length as your spark plug? If it's shorter you'll have more volume inside the combustion chamber and the pressure will read low.

I would have expected a higher compression reading than 135 psi. Do S3 publish any compression stats for their heads?

 

Yeah it’s the same length mate and no they don’t publish any stats they just state that it is valued to have more compression and more power delivery, it’s well in the 150 hour mark used for track for 80 and the rest green laning so I’m sure it due one just by the sound of the engine, piston doesn’t look too good having heat marks all around the rings.

 

Wow, 200 is getting there. 150 is the sweet spot for what I've tested. 135 ok, 120 you need to do smth soon....

 

Is 150 what you tested with the stock head mate as I’ve got a s3 head so surely that should give it between 30-55 c more compression, piston is all out now so I might off just got it in time like you’ve said 120 and it should be done.

 

No mate, that is a general comment, but all engines are similar in this. The highest reading I ever had was 160 on a new K1300R. But I don't think these values change much as physics of rings/tolerances get in the way. Happy to be proven wrong, but I reckon 200 is a yarn from some geezer.

I'm always happy to learn.

 

I'm getting 170 psi on a standard Beta 250 at 125 hours. Down from 185 when new.