Low Compression on top cylinder ... now what?

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robinlh

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Does this mean definate rings/pistons? Or are there other causes...?

What are some things to check for before completely tearing things apart. The motor runs "ok" but WOT is no where near where it should be which is what prompted us to check compression.

Thanks in advance. (hoping my new signature shows my boat/motor info)
 
JB

JB

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Re: Low Compression on top cylinder ... now what?

What engine? What compression?
 
roscoe

roscoe

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Re: Low Compression on top cylinder ... now what?

Could need a head gasket, or a decarb.

Which cylinder has low compression? #1 (top) ?
 
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robinlh

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Re: Low Compression on top cylinder ... now what?

the number 1 cylinder (top) ... we decarbed once (ran out of fuel mixture before the third round, must not get as good of mileage as the poster of the instructions :)) I guess it wouldn't hurt to try it again right?

JB ... the type of engine is in my signature, it's a 1989 Force L-drive, 125hp. The compression is close to zero , I want to think 20-something (I don't remember the exact number, my son-in-law is working on the boat for me), we can certainly check it again.
 
JB

JB

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Re: Low Compression on top cylinder ... now what?

I would go with roscoe's suggestions.
 
roscoe

roscoe

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Re: Low Compression on top cylinder ... now what?

Top cylinder is usually the culprit.
Often just a head gasket.
But could have happened from a lean running condition on the top carb, in which case, expect to see damage when you open it up.

Keep us posted.
 
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robinlh

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Re: Low Compression on top cylinder ... now what?

Roscoe ... I notice you said "just a" head gasket ... :) is that a fairly easy replacement on this engine? (My son in law is a mechanic ... big rigs, cars, and now learning boats). I am keeping my fingers crossed with regards to other damage.

Should I go ahead and try the decarb one more time before we move on to opening up the motor?

Thanks a bunch guys
 
roscoe

roscoe

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Re: Low Compression on top cylinder ... now what?

Head gasket is very easy on this engine. Except for the hard to reach bolts as it is an l-drive, sitting down in the boat.

"just " a head gasket, sure sounds better than broken rings and a scored cylinder, doesn't it? :)

Remove head, be careful not to break any bolts off. If he breaks any bolts off, it could turn into a several day project.

Clean it up, check for a warped head, and piston/cylinder damage.
New gasket, torque properly.

Keep us posted.
 
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robinlh

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Re: Low Compression on top cylinder ... now what?

Thanks a bunch ... and yes ... "just a" head gasket sounds WAY better. I will let you k now what we find.
 
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