Johnson V4

Thanks

Lack of compression is usually due to either a hole in the piston, broken/damaged piston rings or badly damaged cylinder walls (or a combination/all of the above.)

Fixing this problem isn't necessarily that difficult or terribly expensive. If your engine runs OK now (an I HOPE you're running it with "muffs" or in the water,or you have probably ruined your water pump already...) you may be able to 'bandage' the problem by just replacing the piston/rings with a good hone job (if the cyl wall isn't in bad shape) or having it bored may not be too expensive if you do all the teardown yourself. Since it's a 2-stroke engine, it's not that difficult since you don't have to deal with valves, etc. Pulling the heads off is usually a matter of a few bolts (you will need to have new head gaskets for when you put it back together.)

If you have zero confidence (and don't have the will/time to read a manual) having someone else with mechanical experience help you could save you money. Finally if you have to take the motor to a marine engine repair shop will cost you money and like a previous poster said, may not be worthwhile, but it wouldn't hurt to ASK how much.

Jeff M

Rob

In order to improve compression, you need to lessen or eliminate places where the fuel/air mix can excape. Check the head gasket, inspect the top of the piston and look carefully at the cylinder walls; it should be fairly obvious what the problem is.

Before I tore down my engine, I would carefully redo the compression test, and then do it again... The individual who 'tested' it may have been looking for a lower price and fudged on the results. Just a possibility. The compression should be within approx 10lbs of each other or less. Closer is better. For example, if you have an older 4 cyl OMC outboard like I do, you might find something like this:

Cyl 1: 100lbs Cyl 2: 97lbs Cyl 3: 101lbs Cyl 4: 99lbs

This would be acceptable.

However something like this would show a problem:

Cyl 1: 100lbs Cyl 2: 97lbs Cyl 3: 101lbs Cyl 4: 79lbs

If you've run the test several times and this is what you see, the engine may run (sorta) but Cyl 4 has a serious problem. Remember, always do compression tests with the throttle wide open.

Compression testers are cheap and anyone who has an engine in their garage (lawnmower, outboard, inboard or automobile) should have one.

Bill Grannis service manager

If the engine does not show signs of discolored paint on the heads from overheating, AND you want to mess with it, a 21 year old OB is not old if taken care of, if it is corroded, filthy, signs of oil/gas leakage, bad seals in lower, shifts funny, then let it go as parts. I have a 1985 Merc 4 cyl that is like brand new, compression 140 to 145 across all 4, you could eat off the heads. Same as my 1989 15 HP Mariner. But I seen other OB's only 5 years old in 10 times more used condition than mine, from neglect, and not having maintaining them. Watch out for discolored heads on any outboards!

If you are selling with a bad cyl, then let the buyer know he has an issue, he may not mind doing it himself or getting it done if he likes the boat and/or motor.

Mike

Being a 21 year old motor, it probably would not be economically feasible to repair it, unless you planned on keeping it for a few more years. If it is a salt water motor, then it is not worth fixing.

Bill Grannis service manager

So is it possible that the engine failed the compression test simply because the spark plug hasn't been firing properly in the past?? Thanks

"GC" <mobaccREMOVE@tig.com.au> wrote in message