Cylinder compression

trailshredder

trailshredder

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Thought I would check my compression on my mercruiser 140 yesterday. I got 60psi on both outer cylinders and absolutley nothing from the center two. I find this kind of unusual and thinking I am doing something wrong or missing something. Especially since the plugs all look fine as far as not silty. wouldn't it hardly run at all with no compression on 2 of the 4 cylinders? I have to use the rubber nozzle attachment for my compression guage since none of my threaded ones seem to thread on. Thought it was 14mm but doesn't seem to want to start threading in. Pretty sure I am holding it tight enough to seal but not sure how to tell for certain. Thoughts? attached is a picture of the plugs (which I will be replacing with NGKs or ACs).
 

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trailshredder

trailshredder

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Re: Cylinder compression

I did get my 14mm to finally thread in. Not looking good though, I am leaning toward a head gasket since it is the 2 center adjacent cylinders that are low. they read 120-60-55-105 from the front to back. Thanks Don for the info.
 
fuzzybob

fuzzybob

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Re: Cylinder compression

Have you looked at iboats? They host this forum....go to the top of the page and on the left side click on marine store. Good luck on your project.
 
trailshredder

trailshredder

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Re: Cylinder compression

Thanks fuzzybob! Ends up that the price is very competitive! Its on order. My first gasket job on a boat engine, hopefully not very much different that an automobile! Doesn't look too bad from the surface!
 
Bondo

Bondo

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Re: Cylinder compression

Ayuh,... What vintage is it,..??

We'll see if We can scare up a Shop Manual for ya....
 
trailshredder

trailshredder

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Re: Cylinder compression

A shop manual would be great help. 1976 Mecruiser 140, inline 3.0L 4 cyl. I have tried a few parts sites based on the engine serial number to no avail. There is a number on the tag that reads 4442071 and a number 2770087 GM stamped on the engine block. Thanks a bunch!
 
trailshredder

trailshredder

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Re: Cylinder compression

Got it tore apart tonight. Was a head gasket failure, see pics.
 

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trailshredder

trailshredder

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Re: Cylinder compression

Does anyone have any torque values for the heads and intake/exhaust manifold. I have seen various values for the heads, 100 ft.lbs. and 130 ft.lbs? Is there a break in (take it easy time) to break in a new headgasket?
 
F

Fordiesel69

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Re: Cylinder compression

If using torque-to-yield bolts, absolutly not, and you cannot retorque even if you wanted to. If using studs or regular nuts typically not either, but I alway just recheck them after a few heat/cool cycles. Some gasket matieral compresses, others don't.

Headgaskets do not have a break in period. Run it as hard as you want.
 
Don S

Don S

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Re: Cylinder compression

Marine gas engines do not use torque to yield head bolts.

Trailshredder, what is the Merc serial number for your engine.
 
RogersJetboat454

RogersJetboat454

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Re: Cylinder compression

trailshredder said:
Got it tore apart tonight. Was a head gasket failure, see pics.
Click to expand...

Don't know if you've put this back together or not yet.

But....... did you happen to put a machinist square across the head and block and check the clearances with a feeler gauge? Your gasket may have not just failed on it's own. You should check the head and deck surfaces to ensure they aren't warped.
 
trailshredder

trailshredder

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Re: Cylinder compression

Not together yet, waiting on gaskets. The head is at a machine shop right now getting cleaned and inspected. I'll be checking the block flatness tonight.
 
A

alilley

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Re: Cylinder compression

that was a smart move have that check out.
this must be a common issue on these motors as i have pulled 2 of them apart. first being the one in my boat which (and you might awant to double check this) was blown in the same spot as yours but my block was cracked there as well and the head in the same spot. the second one i pulled appart i currently being rebuilt. both of these motors had that tin head gasket on them and burned in same spots as yours is.hope the best of luck to you
 
trailshredder

trailshredder

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Re: Cylinder compression

Well, this project keeps getting uglier. Found out the head has some cracks in it. Waiting to see if he thinks it can be repaired. Bummer! Any good sources for used parts out there?
 
trailshredder

trailshredder

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Re: Cylinder compression

Can anyone verify that a 936-5544 is the part number for the engine with serial number 2770087.
 
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