Scored Cylinders: What to Do???

HerbieJ

Cadet
Joined
Oct 3, 2009
Messages
19
I recently bought my first boat, a used pontoon, with a used 1995 (new in 1998) Mariner 50 on it - a 4 cyl., 4 stroke. The seller said it had a "knock" in it and there might be a head gasket problem. He said he over-revved the engine trying to get the boat on a trailer. He also said he put too much oil in it. I siphoned off nearly 2 quarts ABOVE the full mark on the dipstick - clean new oil. Then I drained the oils sump all the way: black, dirty oil came out. I then refilled the sump and started it (in barrel). It started right up. It ran a bit rough initially and continued to have a hesitation upon accelerating, which I'm guessing is carbeuration.

That?s the history part: here?s my concern. I've run multiple compression checks and always get a lower reading on #4cyl. (Last check typical: #1-107; #2- 100; #3-105; #4-90). I've had the motor idling (mostly) in a barrel for approx. 45 minutes using a fuel additive to free sticking rings, but it didn't help. I pulled the head yesterday and found cylinder scoring - very light on #s 2 + 3: not enough to feel, but I can feel the scores in #4 with my fingernail. Cylinder # 1 has no scoring. I have fairly good pictures posted at http://www5.snapfish.com/thumbnailshare/AlbumID=3088767014/a=119005847_119005847/ or I could email better ones to anyone interested in helping if given an address. I?ve also included pictures of the head. I don?t see anything remarkable there, but perhaps you might. The head gasket was good.

What needs to be done here? Is this motor worth repairing, and if so, what should I expect to pay? I can deliver the powerhead to a repair facility stripped down to the cylinders, but would prefer the facility to open the crankcase cover and do whatever needs to be done with the pistons, rings, and bearings as well as any boring / refinishing. Cost will be the dewtermining factor.

As always, any thoughts will be much appreciated.
 

robert graham

Admiral
Joined
Apr 16, 2009
Messages
6,908
Re: Scored Cylinders: What to Do???

Based on your note and photos, if it's knocking then you've probably got a problem that will require removal/disassembly/repair of power head, but if it's not knocking then maybe you can button it back up, have carbs cleaned, adjust valves,etc. and the motor may run fine. A little cylinder scoring is not a good thing but the motor can run pretty well with what I see in the photos. Good Luck!
 

HerbieJ

Cadet
Joined
Oct 3, 2009
Messages
19
Re: Scored Cylinders: What to Do???

Well, that's encouraging news! But I still have a consistent 15 point differential between compression high and low, and I don't know what the pistons and rings look like. Nor do I know why I've got scoring. I'm already having to go for a head gasket and carb kit(s) to put it back together. I'd just as soon fix it right while it's apart, but I need to know what I'd be looking at dollar-wise. It would be very difficult for me to take the motor off the boat and go for a local estimate, (66 years old!), although I could probably pull the powerhead. But that's more disassembly and I don't have the special tools I should have to do it. I'm hoping to draw on the experience of people like yourself who have a feel for what things cost. I've got about five months to get things done, once I know which way to go. In the end though, yours may well be the advice I'll follow. Thanks much for it, and for checking out the pictures.

Herb
 
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