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Outboard motor compression

Posted By: Crappieshooter

Outboard motor compression - 08/06/21 11:53 PM

Is 95 psi enough compression for an outboard motor. Looking at buying a boat and was told the compression check showed 95 psi on all cylinders. Good or bad?
Posted By: PaulGrapevine

Re: Outboard motor compression - 08/07/21 12:51 AM

2 stroke or 4 stroke motor? If it’s a 2 stroke then I’d be okay with it.
Posted By: Topwater2

Re: Outboard motor compression - 08/07/21 01:22 AM

Told? Get it in writing.
Posted By: Pat Goff

Re: Outboard motor compression - 08/07/21 01:50 AM

Depends on the motor.
95 is fine on a old Johnson.
On a V6 merc it would be sick.
Posted By: Crappieshooter

Re: Outboard motor compression - 08/07/21 02:44 AM

2002 Mercury 2 stroke.
Posted By: Coolarrow

Re: Outboard motor compression - 08/07/21 02:45 AM

My old 96 Johnson 150 has 120 on all 6 so I’m not sure. What kind of motor and year? The
Posted By: Coolarrow

Re: Outboard motor compression - 08/07/21 02:46 AM

Originally Posted by Crappieshooter
2002 Mercury 2 stroke.

HP?
Posted By: Coolarrow

Re: Outboard motor compression - 08/07/21 02:50 AM

I know a 90 hp has about 120 psi in that year model range.
Posted By: FlyFX

Re: Outboard motor compression - 08/07/21 03:23 AM

always take a compression gauge, some lube and a plug wrench to survey a boat
Posted By: Pat Goff

Re: Outboard motor compression - 08/07/21 04:14 AM

Compression gauges can vary from one to another. What you’re really looking for is a misfit cylinder. Sick motor will have five at 120 and one at 90. On your three cylinder take all the plugs out, pull the kill switch and spin each hole. If they are all the same it’s what you want. If one is more than 10% different there is an issue.
Posted By: pil,b

Re: Outboard motor compression - 08/08/21 04:00 PM

Leak off test
Posted By: Crappieshooter

Re: Outboard motor compression - 08/16/21 03:17 AM

Thanks for the replies, passed on the motor.
Posted By: Gamblinman

Re: Outboard motor compression - 08/21/21 03:55 PM

Compression check is really only to determine if you have bad cylinder. If you want to know the real health of an engine, a leakdown test should be performed.
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