Yamaha TRX850 Enthusiasts Forum

Can anyone tell me what compression I should have in the cylinders on a TRX?

Today i measured it as 35psi and 55psi. I think this is way under spec.

More than likely the biggest reason it wont start too.

Check your valve clearances, this may be the culprit.
Just hope the inlets are not damaged. Is it a 95-96 model???

The service manual lists standard compression as 1,200kPa / 12Bar at 300rpm, which is approx 174psi

Did you do the compression check with a warm motor and the throttle wide open? I have seen people do a compression test with a closed throttle and wonder why the reading is low.

Thanks for the feedback.

I repeated the compression test this morning wet/dry & throttle open/closed all on a cold engine as it wont start. I have attached the results below.

I then checked the valve clearances and found all the inlets are touching the cam. I could not even get a 0.05mm feeler gauge in between the cam and bucket.

I have a couple of questions if anyone could help?

1, Has anyone else seen similar readings on their bikes?
2, Is the lack of clearance on the inlet valve a sign of a larger problem with the valves and valve seats?
3, Is the 20psi increase between dry/wet compression tests enough to consider a deeper stip down investigating the rings and bore condition?

Thanks for the support.

I sent the bike to my local repair shop. I just got the diagnosis.

A top end rebuild is required as all valves have "mushroomed" heads. Inlets are really bad. This is going to be an expensive fix.