Compression after replacing head gasket

[jpian0923]

So, I replaced the head gasket because of low compression in cylinders 2 and 3...around 50 to 60 psi. Now with the new gasket and Moyer used Head I'm not sure the compression is much improved. Engine is still out...in my cabin.

Also, while having the head off I filled all cylinders with an ounce or so of MMO on several occasions to prevent them from locking up and to free the rings, in case that was an issue. By the next day MMO was still in 1 and 4 cylinders but not in 2 and 3.

There is nothing attached to the engine right now so I can't start it to test compression. Here are my questions:


What would compression numbers be like just hand cranking? (have not tried it yet)
Is the MMO seeping passed the rings an indication of anything?
Should I continue with MMO treatments assuming it will free the rings? (in case that is the cause of low compression)
Can I remove pistons and rings without removing the head? (I destroyed one head already and all the studs using the wrong puller)

[hanleyclifford]

Handcranking will not yield any useful information about compression. The fact that #2 and #3 will not hold oil overnight is a concern but I would not rush to judgement. It could be stuck or partially stuck rings or possibly unlucky line up of ring end gaps. I would proceed with the MM oil treatments. I would get the engine running and check compresion after an hour or so. Removing pistons will require getting the engine out of the boat. It is possible to take the pistons out thru the bottom.

[jpian0923]

I was afraid of that

[edwardc]

Originally Posted by jpian0923

There is nothing attached to the engine right now so I can't start it to test compression.

If the starter's still attached, all you need is a couple of automotive battery cables to connect the battery, and a remote starter switch. You can crank it right there on the floor.

[hanleyclifford]

I have to retract something I wrote. You could theoretically take the engine down in the cabin but most of us regard that as an emergency, no choice scenario. You could also put the starter back on and turn the engine without starting it to see if compression has been improved. Spin it a little first with the MM oil in the cylinders, spark plugs out and a thick towel on top to catch the mess.

[jpian0923]

Actually I went to the boat tonight and the compression in each cylinder seems about the same when hand cranking and holding a finger over the spark plug hole.

So, I think the MMO actually worked but I won't know til I get it all back together. If at that point I find out I was wrong I will probably take it all apart again () and/or have the boat hauled and bottom painted and deal with a slew of other problems I have including this one and...mis-aligned prop shaft or bent prop shaft (not sure). My list is getting longer and longer but whether I'm working on the boat or sailing it, I like being on it either way and will keep doing what I have to to get it ready for summer.

I appreciate all the help and next time would not chose to work on the engine in the cabin except for the fact that all my tools are there. It's much harder doing it my way despite what I thought was going to make it easier for me...it didn't.