76 150 tower

Searay 150merc

Seaman Apprentice
Joined
Aug 1, 2008
Messages
34
what is the lowest compression needed per cylinder. I tested mine and they were 95 psi on all. Any help would be greatly apreciated
 

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
27,161
Re: 76 150 tower

Compression Guages need to be consistant and reliable (like clocks). Since you measured 95 PSi in all cylinders, it is likely your gauge is consistant, but not reliable.

Another compression guage would likely show that they are really 100+PSI. There are no published standards for compression, only the difference between them(<15%). it sounds like your cylinders are fine.
 

hkeiner

Lieutenant Junior Grade
Joined
Oct 17, 2006
Messages
1,055
Re: 76 150 tower

Below is a quote from my Mercury OEM shop manual regarding compression specs. This may give you an idea as to the ideal compression range for your motor. As pointed out, your 95 psi readings may be innacuarate if your gauge is innacurate and using several different gauges to see what they read on average may provide better information. If this is impractical, another thing to do is to spray some oil into the cylinders (through the spark plug openings) before doing the compression test to see if the compression readings go up substantially. If they do, this may indicate low compression due to leaky rings and such. If the compression does not change, then you may be good.

Another thing to try is to decarb the motor (using Seafoam or equivilent) to see if that improves the compression readings you get. Sometimes carbon can cause piston rings to stick and leak a bit.

Compression / All Models ? Using a fully charged battery, throttle shutters wide open and cylinder block warm ? 110 ? 135 psi (753.3 ? 924.5 kPa). Variance between cylinders should not exceed 15 psi (102.7 kPa)
 
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