fixing Bubbling plug /increase compression?

[ArtJ]

I have had a cylinder which has lower compression than the others
(around 80 psi at best) The plug in this cylinder also bubbles.

I am wondering if installing a helicoil would fix both issues?
How is a helicoil installed?
I assume drilling is part of the process. Can it be done (carefully) with
the head not being removed, possibly by stuffing a small greasy
piece of rag in the plug hole while drilling out for helicoil and then
retrieving the rag with tweezers and vacuuming out the cylinder?

Alternatively, Can the plug threads be sealed better by using
some type of loctite or other sealant? keeping in mind that the
plugs are removed bi weekly during the winter storage to turn engine
over and squirt in MMO,( I just keep plugs finger tight in winter storage.)

Thanks

Art

[Bob Grenier]

Art; are the threads striped? If not striped, no need to remake the threads. The threads are not what seal the plug; that little crush washer is the seal.

This would not change your compression; if you have low compression it will be lost past the rings or valves. (80 is not real bad)

Check the seat and the washer itself for damage. A small scratch or a flake of rust may not let the washer seal well. Try new plugs and see if it still bubbles.

When reusing plugs, be very careful this is when you can strip the plug threads because the crush washer has already been crushed.
Bob

[ArtJ]

Thank you Bob.

For Some insightful and helpful hints

Appreciated Art

[ndutton]

Bubbles? What liquid is puddled in the spark plug recess for the compression to bubble through and where did it come from?

The spark plug crush washer won't affect your compression measurement as the tester replaces the plug and its washer. Also, you could tell pretty easily if the plug threads are stripped. I agree that 80 isn't horrible but the difference between the cylinders indicates an issue.

I don't like what I'm thinking but I'd start looking for a hairline crack in the head in the vicinity of the offending cylinder. That would explain the puddling and the different compression. I really want to be wrong on this one.

[ArtJ]

Thank you as well for the suggestions.

I have plenty of time since boat is laid up for the winter.
i will look for cracks as you suggest.

Appreciated

Art

[67c&ccorv]

Art - is the leaking plug located near the lifting eye bolt holes?

[sastanley]

magnify!

Art, When I went shopping for an engagement ring, I bought a reasonably priced 10X loupe. It was really just to make sure the jewelers weren't ripping me off. I use it all the time now..its field of view is small, but you can see all kinds of stuff with it! This would be a good tool, or maybe even a less expensive magnifying glass to help with inspection.

I think what 67C&C is getting at is there have been some reports of the lifting eye not distributing the loads well, and cracks developing in the head as a result. This would be Cyl. #3 & maybe #2 I think.

[ArtJ]

Thanks again for the info

I will look into a magnifying glass.
The cylinder is the second from the front.
The Engine has not been out of the engine in at least a dozen years,
before that I don't know.

It is quite cold in Boston lately, around 10 degrees in Southern NH last night
so it may be a few days before I can look.