Low Compression

[Northwood]

Need a little info. I have a 3 cylinder 70hp Evinrude motor. When I had it tuned up this year the mechanic said #1 cylinder had lower compression than the other two cylinders. #1/110#...#2/3 140# is this a serious problem? The motor is a 1995 model but was in storage for 5 years when I purchased it. It runs smooth as silk but the idle is a little rough. Thanks for any help..

[Kyle Sandberg]

you might have a leaky gasket or sealing problem letting the compressed mixture to escape. My .02

[pfluemis]

Add 1 can of Seafoam to each tank of gas and run it the rest of the summer. At the end of the season, as your getting the boat ready for storage, if you do that in Ill, retest the motor. If things improve, then it was a carboned/sticking ring, if they don't improve, that would be the time to tear it down and find the cause. It would not hurt to monitor the situation in the mean time. Check the compression every couple uses or every use to make sure it's not getting worse. The 2 most common problems with that motor is, like all brands, the oil injection can go out at any time. The other problem is the #2 cylinder leaning out in the mid-upper rpms (4000-4500). There have been service bulletins adressing this, that any dealer, that was a 'Rude dealer in that era or earlier, can refer to.

[ChemMechanicInc]

Yeah, I had a 96' Johnny triple, center cylinder stuck on 4th of july weekend about 5 years ago.

REEEEEEEEEE'eeeeeeee'eeeeee'rrrrrrrrr'TINK!

I bought a new engine, consequently.

[shamrock7]

Make sure that it has the tell tale discharge at the top of the cylinder block rather than down on the exhaust manifold. This motor was notorious for developing a steam pocket in and around the #1 cylinder and frying the engine. This was more likely to happen on pontoon boat applications. Why? I don't have a clue. This will not improve your compression but it may keep it from getting worse. Normally, we consider a 10 % variation on compression to be acceptable. Your rough idle is directly attributed to the compression issue. As the compression gets worse, you will start to notice much harder starting and really rough idle with difficulty getting the motor into gear without it dying. I would reccomend pulling the head and taking a look. If any of the cylinders have any scoring, its time to to an overhaul. If all the cylinders look good, put it back together with a new head gasket and retest. Head gasket leaks that are small can be hard to see. And it is a relatively easy fix. Go to the library and you can find a manual that will have the torquing sequence or your dealer might be willing to give you a copy of that page of the Service Manual.

Good Luck