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Outboard motor compression #14086625 08/06/21 11:53 PM
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Crappieshooter Offline OP
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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?





Re: Outboard motor compression [Re: Crappieshooter] #14086666 08/07/21 12:51 AM
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PaulGrapevine Online Content
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2 stroke or 4 stroke motor? If it’s a 2 stroke then I’d be okay with it.

Re: Outboard motor compression [Re: Crappieshooter] #14086696 08/07/21 01:22 AM
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Told? Get it in writing.


FishKen
Re: Outboard motor compression [Re: Crappieshooter] #14086725 08/07/21 01:50 AM
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Pat Goff Online Content
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Depends on the motor.
95 is fine on a old Johnson.
On a V6 merc it would be sick.


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Re: Outboard motor compression [Re: Crappieshooter] #14086775 08/07/21 02:44 AM
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2002 Mercury 2 stroke.





Re: Outboard motor compression [Re: Crappieshooter] #14086776 08/07/21 02:45 AM
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My old 96 Johnson 150 has 120 on all 6 so I’m not sure. What kind of motor and year? The

Re: Outboard motor compression [Re: Crappieshooter] #14086777 08/07/21 02:46 AM
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Originally Posted by Crappieshooter
2002 Mercury 2 stroke.

HP?

Re: Outboard motor compression [Re: Crappieshooter] #14086785 08/07/21 02:50 AM
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I know a 90 hp has about 120 psi in that year model range.

Re: Outboard motor compression [Re: Crappieshooter] #14086822 08/07/21 03:23 AM
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always take a compression gauge, some lube and a plug wrench to survey a boat


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Re: Outboard motor compression [Re: Crappieshooter] #14086859 08/07/21 04:14 AM
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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.


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Re: Outboard motor compression [Re: Crappieshooter] #14087865 08/08/21 04:00 PM
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Leak off test

Re: Outboard motor compression [Re: Crappieshooter] #14096530 08/16/21 03:17 AM
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Thanks for the replies, passed on the motor.





Re: Outboard motor compression [Re: Crappieshooter] #14103296 08/21/21 03:55 PM
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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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