New old boat question

[wrenchtosser]

Hello everyone - I just bought an old boat for my family (getting the boys off of video games and such). It is a 1989 Sylvan deck boat 15ft with a 1983 115 Johnson. Not being a boat guy and reading some threads I got interested in checking out my engine - probably what I should have done before I dropped $2500 into the guys hands. I did a compression test and three cylinders were 120-125 and one was 95. So with this new found information I don't know what to do. Drive it and worry about it later? It is the top right cylinder. It does not look "water washed". Any thoughts from the experts?

 

[boobie]

Re: New old boat question

Pull the head on that side and check out the head gasket and the cylinder. It may be just stuck rings, but check it first.

 

[wrenchtosser]

Re: New old boat question

Is it safe to run for a little while before I recheck?

 

[boobie]

Re: New old boat question

If it was my mtr I'd do it now. But that is your choice. If you have a problem starting you may catch it before it's to late.

 

[emdsapmgr]

Re: New old boat question

Compression is good when all cylinders are within 10% of each other. Your one is out of that range. That's potentially a problem. Best to pull the head now and have a look before any new damage occurs. The only expense risk at this point is for a new head gasket. You may be lucky and find that it's just a bad head gasket seal ring.

 

[wrenchtosser]

Re: New old boat question

Thanks guys. I read that 'one clyinder' is more prone to blowing a head gasket because of the cooling design. If this is true, might you know if it is the top right?

 

[boobie]

Re: New old boat question

That's the one that gets the hotest but the head gasket can blow on the other cyl's also.

 

[jim j geezer]

Re: New old boat question

Look for scoring on the cylinder wall(s) while you have that head off! Compare with the 2nd cylinder. <-- This is cheap "scuttwork/homework" that pays you back many times over! If it's scored... $$$$$$$$$$$$$$
Or.... Roll the dice and run it. Be prepared to be towed in one sunny day while your family showers you with frowns....
ALL. THE. WAY. IN.

 

[wrenchtosser]

Re: New old boat question

Thanks a lot guys. I ordered a new head gasket and when it gets here I will pop the head off. One Q: when I spray oil in the cylinder the compression remains the same. Does that imply head gasket? I took that as a good sign.

 

[emdsapmgr]

Re: New old boat question

Spraying oil in a cylinder can distort/skew the compression readings somewhat higher. After cranking it over for a minute or so, the extra oil in the cylinder will dissipate and the compression readings will eventually go down to a more "normal" reading.

 

[jim j geezer]

Re: New old boat question

wrenchtosser?
The short answer is: Yes. It DOES IMPLY "a bad head gasket." BUT... It ALSO... IMPLYS... other stuff too! Stuck or broken rings, for instance.

I've found that the ring NEAREST the piston on engines that use more than a single ring, such as your outboard (and my 1951 Citroen CV "Corporal") can have that 'oil-wiper' ring break and score the dickens outta the interior cylinder wall, and the thing'll still run.

Translation: THINK about pulling the carb assy, followed by the reed valve assy, so you can access the connecting rod's "cap bolts".
After removing those bolts, you can use a small-diameter wooden rod and either push or drive out that cylinder's piston.

Only then can you lay eyeballs on that pesky 'oil-wiper' ring and make an informed assessment.

Sorry to put a crimp in your morning coffee!
Good luck!
Geezer Jim