compression numbers?

[1979 Quartermasters]

Wondering what the compression numbers should be for 1991 Yamaha 225. Anything else to look for on this motor.

Thanks

Ken

 

[gm280]

Re: compression numbers?

You have to remember that compression numbers are a mere indicator of engine condition and not a one size fits all thing. With that said, if those compression numbers are all within a 10 to 15% window of all cylinders, then for the most part the engine will run. Higher numbers are better of course, but not the only determining factor if an engine is good or bad. So let the numbers between all cylinders be your guide and not the good or bad motor decision issue... I've heard folks with 85 PSI and even lower numbers run all day long without problems...

 

[JB]

Re: compression numbers?

Agreed. Gauges, conditions and technique vary too much to say that you have to get some minimum psi, but there will be only one gauge, one set of conditions and one technique used in a test. A healthy engine will compress about (+/- 10%) the same psi on all cylinders.

Signs of trouble will be one or maybe two cylinders that compress less than 85-90% of the others.