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3.0 mercruiser # 4 around 25pis on compression check

R

Redmantaylor

Member
Ok I got on #1 170
#2 160
#3 170
#4 025 psi
on a compression check the boat had been setting up for about 5 years. No water in the oil What could be some of the problems that would cause that Thanks for any help
 
Get this engine fired up while on the garden hose and water muffs.
Operate it for a while at normal operating temperature.
Now take another cylinder pressure reading on all 4 cylinders.

If the #4 cylinder remains low..... DO NOT remove the cylinder head until after first having done a "cylinder leak-down" test.


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..."my motor had a groove around the cylinder about it inch and a half down "

How do you know this? With a bore scope?

Jeff
 
Naw,.... Chevy motors are over-bored .030", or .040", All the time,....

Most common pistons can be bought in .030" over, .040" over(which is fairly new), 'n .060" over,....

Motors bored .060" over sometimes have issues because of core-shift when the block was cast,...
Thin cylinder walls can happen,....
 
A .040" over-bore means that only .020" has been removed from the cylinder wall.

.030" would have been a safer amount.... but you won't/shouldn't have any trouble!



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