Compression Values

R

resolute

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Jul 6, 2009
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Having an issue with performance on a recently purchased used boat. It completely bogs down when put under higher throttle. I replaced the head gasket which had a clear burnout between the 2 and 3 cylinders. The compression is running at about 110-115 for all four cylinders after. I'm worried that the rings might be shot and am wondering what the value should be.

Specs 1987 Mercruiser 3.0L I-4, 130 HP, Alpha 1 outdrive

thank-you :)
 
mkast

mkast

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Re: Compression Values

Do a cylinder leak down test. It will tell you why the engine has a lack of compression.
 
R

resolute

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Re: Compression Values

yeah working on borrowing a leak down tester from a friend. That will help alot. Found one bent push rod while changing the gasket but everything else valve train wise didn't look to bad.

I was hoping somebody could give me whats reasonable on a seasoned engine vs fresh engine so I know what i'm shooting for. :confused:
 
JustJason

JustJason

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Aug 27, 2007
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5,319
Re: Compression Values

as far as your numbers go. 115 is getting down to the lower end of the scale, but certainly servicable and runable if the boats in good tune. If the numbers are even across the scale then leave it, or try a valve adjustment and see if that bumps it back up a few psi.
You can go to the "adults only" section and pull a manual for your motor that will go over the procedure.

Other than that... describe your "bog" some more. Does it flutter out for a second then pick back up. Are you getting WOT out of the motor?
 
mkast

mkast

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Re: Compression Values

resolute said:
I was hoping somebody could give me whats reasonable on a seasoned engine vs fresh engine so I know what i'm shooting for. :confused:
Click to expand...

According to Mercruiser specs are 140 psi.
 
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