Compression Question

[WaterDR]

I am looking at buying a 1200 SUV, 2002. The unit has 69 hours on it and is in near perfect condition. All maint. done...stored indoors etc... The unit is very clean.

The owner and I checked the compression and only got 85 psi on all cylinders. However, the unit seems to run fine. The fact that it is this low and the same in all locations, would seem to tell me we either did it wrong, of the guage we used is bad. I would think at 85 psi, it would run like hell...if at all.

Any thoughts?

We had all plugs out when we tested it and simply cranked the motor over.

How many hours should you be able to get on one of these before needing a re-build?

[dsolie]

Re: Compression Question

It's your gauge... The fact that they are even is the most important part...

My thought?? Water test, water test!!

[WaterDR]

Re: Compression Question

Dan, that is what I was thnking. I could see ONE bad cylinder and have the thing still run, but three this bad....no way.

Anyway, what do you mean by "water test"? Are you referring to a a test drive, or is there a separate test to which you are referencing?

[dsolie]

Re: Compression Question

Yup... test ride!

[Madfish]

Re: Compression Question

I believe the compression for this motor - when new - should be 120 psi on all 3 cylinders. I would expect a properly broken in and well maintained Yamaha 1200 motor with 69 hrs to be between 110 and 120 psi. Get yourself a quality cylinder compression gauge, and hold the throttle wide open when turning the engine over during compression check. On a multiple cylinder engine, compression should be within 5 psi of each other. 10 psi or more difference between cylinders and you have a problem.