Cylinder scoring

[RustyC]

I am looking at purchacing a 1997 20' boat with a 97 Johnson 150 HP motor with less than 100 hours. The owner informed me that one of the cylinders has scoring on it. How big a deal is this scoring and what would I be looking at repair wise on this motor. Thanks for any input.

 

[Hooty]

Re: Cylinder scoring

The easiest way to determine the condition of the cylinders is do a compression test. If you have questions about how to do it, do a search for "compression test". There shouldn't be more then a 10% variation between any of the cylinders. If you like, do the test and then post the results back here, on this same thread, and someone will help you analyze the results.<br /><br />c/6<br />Hooty

 

[Solittle]

Re: Cylinder scoring

If you have one or more cylinders with more than a 10% variation as Hooty said then the next step would be to pull the heads and examine the cylinder walls.<br /><br />Worst case is to rebuild the bad cylinder(s). You only have to repair the one that is bad although many will advise a complete rebuild. OMC says it is OK to only do the one that is out of spec.

 

[RustyC]

Re: Cylinder scoring

I spoke with the owner of the boat. He says that the compression on one cylinder is at 40 the rest are at least 100. He says that he doesn't know how it happened. I plan on going down to look at the boat and will do my own compression test. The boat and motor are not that old and he says there are less than 100 hours on the motor. <br />Any ones thoughts on what to look for?

 

[Fouled Plug]

Re: Cylinder scoring

Could be caused by a lean condition, or overheating. If the bad cylinder is indeed at 40#, you will need to tear the motor down and repair. I would hope the engine damage is making this boat package very inexpensive.

 

[Hooty]

Re: Cylinder scoring

... or it may just be a blown head gasket. 40psi is pretty low though. Do your own test and if it really is that low, pull the head and have a look.<br /><br />c/6<br />Hooty