3.0 Compression problem

[MTBoat]

I have picked up a nice boat and trailer and comes with 1991 3.0 Mercruiser.

It has a cracked jacket, not block and no oil in engine, so JB'd and have done this before with good results.

However, upon doing an initial compression check, all cylindars come up very nearly the same, about 100 lbs on my guage, and the second cylander from the front comes in at 30. It turned over nicely when plugs were out, no strange sounds.

Is there some usual culprits to consider here, can it still run but with reduced power, or is it going to be a major to use.

Appreciate any experienced feedback on this, or possible solutions.
Thanks

 

[Bondo]

Re: 3.0 Compression problem

I have picked up a nice boat and trailer and comes with 1991 3.0 Mercruiser.

It has a cracked jacket, not block and no oil in engine, so JB'd and have done this before with good results.

However, upon doing an initial compression check, all cylindars come up very nearly the same, about 100 lbs on my guage, and the second cylander from the front comes in at 30. It turned over nicely when plugs were out, no strange sounds.

Is there some usual culprits to consider here, can it still run but with reduced power, or is it going to be a major to use.

Appreciate any experienced feedback on this, or possible solutions.
Thanks

Ayuh,.... Ya say All the same, then 1 is at 30 psi,..??

If All 4 are at 100 psi, you've got a rebuildable core motor, not really a Runner, though it'll probably run,....

If 1 hole is at 30 psi, it needs Fixin',...

Do a leak-down test to see where it's leakin',... Valves or rings,...

 

[MTBoat]

Re: 3.0 Compression problem

We did a wet test and it only went up a couple lbs.
We pulled the valve cover and the valves seem seated ok, but, we'll get a tool to push em out and see how they seat.
We saw some rust/pitting on the inside 40% of the very upper 1/2 inch of the cylander wall, on the problem cylander.

Is that usually enough to actually drop the compression 70%?

We are just trying to imagine if there are ways to get a decent engine up and running without a full blown $1500 overhaul. Meaning, what if we hone the cylander walls, put new rings on all, and do a valve job and new head gasket after throughout cleaning. Is it likely we might be all cylanders back to 130lbs or so, vs a brand new 145plus. The point being, the boat is older and would be fine with a nice running engine for the next 5-10 years for possibly a few hundred bucks and enjoy the boat.

OK, just appreciate anyone that has past experiences that might shed some light on such concepts.

thanks much