Before winterizing Aurora II's A4, I checked the compression. Much to our chagrin, we had 0 psi in cylinders 3 & 4. Cylinders 1 & 2 were fine at 110 psi. Assuming we had a blown head gasket, we Proceeded with the lay-up, expecting to have to replace the head gasket next spring. After the
winterizing, Renee suggested that we check the compression again. We did and I read 110 psi in all 4 cylinders. It appears that the MMO poured into each cylinder and running the engine for 5 minutes did the trick. Has anyone encountered a similar situation? Should I be concerned that we do indeed have a blown head gasket? If we do have to replace the head gasket, has anyone done this without pulling the engine?

     No problem with pulling head while engine in place. I did a valve job with engine in place - - - had to use a mirror due to lack of clearance!   Reason #3 & 4 are giving you trouble is because those two cylinders run cooler and therefore gum-up more.

     On "Enterprise"  Triton #625, east coast, I have had to pull the head and replace the gasket once and have pulled the head to decarbon the engine one time after that.  It is really no problem at all.

     When we had the A4 on our boat rebuilt. We found that the blown head gasket allowed water to reach a cylinder and there was some rust starting. It is important to fix it. The work can be done on the engine without pulling it. The head had to be ground so the fit was tight. It runs like a top now. We also put electronic ignition on and it starts right up.

     Valves hanging open are common on the old A-4's.  MMO is great but a hammer on the valve cover (gently) works fine when underway.