1969 Johnson 115HP Compression Question

[Phishin]

I was winterizing my boat yesterday and when I removed the spark plug on the upper left (as I face towards the bow), I noticed that it came loose REALLY easy. Hardly any pressure applied to the plug and it's turning.....

I removed the plug, and there is a pool of oil laying in the cavacity of the head where the spark plug boot attaches to the plug. Hmmmmm.....

Could have the plug vibrated loose? And oil blew by the threads? Is that what happened?

So I check the compression of all 4 cylinders since I have the plugs out, three cylinders have 120-125 psi. The cylinder that had the loose plug and the oil laying under it had 110-115. Could the loose plug caused an air leak and "fried" the rings? Or is there a problem with this cylinder and that's why the oil is under the plug?

Finally, am I ok or do I need to do some work to this because one cylinder is 10 psi lower than the rest?

Thanks in advace.
Steve

 

[Phishin]

Re: 1969 Johnson 115HP Compression Question

Anyone?

 

[1946Zephyr]

Re: 1969 Johnson 115HP Compression Question

Yea, that is a bit uneven, but those numbers are high enough that it'll run fine. Compression isn't too bad for a motor thats 42 years old. I would run a decarb on it and see if things improve.

 

[boobie]

Re: 1969 Johnson 115HP Compression Question

Don't worry about 10 psi. Do a good decarb on it as said above and you should be okay.

 

[dazk14]

Re: 1969 Johnson 115HP Compression Question

+1 - the threads on the head may be on the way out. Easy fix, but chip migration can be risky if head isn't pulled, although we have done them without pulling head, but we also have a boroscope.

 

[Phishin]

Re: 1969 Johnson 115HP Compression Question

What's the best way to de-carbonize this engine? It's about spring time here in Indiana!!