Compression

[scottpellegrin]

1998 Yamaha VMAX 225with 125 hrs on it, I know all the cylinders need to be with in 5% of each other for a good compression test. I'm wondering if someone knows what this motor is supposed to have for psi. I see some motors put out up to 135psi and others 100 psi. I'm looking for a base line to compare to. And also why are some motors different than others?

 

[scottpellegrin]

Re: Compression

Can anyone help?

 

[trendsetter240]

Re: Compression

Compression readings vary depending upon the compression gauge, the person perfoming the test and many other factors.

The most important thing to look for is even compression and above 100psi on all cylinders. The accepted variance is 10% on each cylinder.

Lower compression means less of a seal in the combustion chamber. This could be from worn out rings, scoring on the cylinder walls, leaking head gasket or worn/damaged pistons.

 

[5150abf]

Re: Compression

Ya even a factory manual doesn't list compression numbers, some engines run 90 others are 135+, it is just how they were designed.

My buddy has the same engine I do, his has 145, mine is 125 but both run fine.

The impartant thing is to have all cylinders within 10%, do a base line on your motor now and then you can compare later as you test.

Better to test hot as you get a more acurrate reading.