Re: Mercury compression prob
A model of that year has no head, therefore a head gasket is out of the question, it could be ring related or a hole burned in the piston. Unfortunately that cylinder is down inside the lower cowling and you can't look down the bore, otherwise I would say pull the plug and look down the hole. On that motor the crank has to come out the bottom with all connecting rods and pistons, I have a '77 500 that is the same way. I am told that some Merc dealers won't work on those, according to a local independant that I worked with in the past. Unfortunately I'm thinking this is bad news. If it is, a good used motor may be in your future.
