[Inedible]

Engine is a 2000 model, no information available regarding hours. here

[berserk9779]

Cylinder compression is reported to be:
1. 140
2. 140
3. 125
4. 125
5. 130
6. 130 here

[jumolock1976]

Engine Compression Testing [links]

[sizewraps]

I'm not the most mechanically knowledgeable person around, should the following compression readings raise any red flags?

[Innarita]

A compression test will tell you if your engine has good compression. An engine is essentially a self-powered [COLOR=blue ! important][FONT=inherit ! important][COLOR=blue ! important][FONT=inherit ! important]air [COLOR=blue ! important][FONT=inherit ! important]pump[/FONT][/COLOR][/FONT][/COLOR][/COLOR], so it needs good compression to run efficiently, cleanly and to start easily. [/FONT]
As a rule, most engines should have 140 to 160 lbs. Of cranking compression with no more than 10% difference between any of the cylinders.
Low compression in one cylinder usually indicates a bad exhaust valve. Low compression in two adjacent cylinders typically means you have a bad [COLOR=blue ! important][FONT=inherit ! important][COLOR=blue ! important][FONT=inherit ! important]head [COLOR=blue ! important][FONT=inherit ! important]gasket[/FONT][/COLOR][/FONT][/COLOR][/COLOR]. Low compression in all cylinders would tell you the rings and cylinders are worn and the engine needs to be overhauled. [/FONT]
HOW TO CHECK COMPRESSION
Compression can be checked two ways: manually with a compression gauge, or electronically with an engine analyzer the measures cranking compression. With electronic testing, a computer analyzer estimates compression in each of the engine's cylinders by measuring slight variations in engine cranking speed.
The results correlate well with actual gauge readings, and can be completed in a matter of minutes without having to remove any spark plugs. What's more, the analyzer prints out the results of the compression test making it easy to see and compare the actual numbers.

[pull]

Re: mercury compression specifications

[pavelo]

I am looking at buying a merc outboard - 1997 250 hp EFI with an hour meter showing 178 hours. Compression check shows 100,105,100,110,105,100. What should this motor have for compression with these low hours, or am I being scammed and the motor really has 500 or more hours.

[qleonardomontoyao]

My 74 Johnny has compression at 120 with who knows how many hours on it.
But that is all i can offer you.

[LOUIECCC]

Re: mercury compression specifications

[venom]

I am looking at buying a merc outboard - 1997 250 hp EFI with an hour meter showing 178 hours. Compression check shows 100,105,100,110,105,100. What should this motor have for compression with these low hours, or am I being scammed and the motor really has 500 or more hours. [links]

[lishan1997]

[MacRohard]

Run it for a while and then check it again.

[Tara01]

It's best to start your own thread for new questions.

[andrewegc]

Re: Mercury 40 HP 4 Cylinder 2-Stroke Compression Question

[HopeFlynn7x]

Re: Compression test on 7.4L, are these numbers ok?

[tentative]

What he ^ said. And 'was the engine warm'?

[abitcoinuser]

The spec on my engine is 150 psi . . . So my numbers are close. It is hard to say if my gauge is accurate (cuz it is wicked old). I have 500 hours on the engine and just did a valve job last Fall (getting me to the better numbers listed under "2012"). here