1977 Merc 70hp LEAK

I have a 77 Mercury 70hp, 3 cylinder that I am trying to get right. Today, while running the motor in a barrel, I noticed water seeping out of the middle spark plug area. The 3 spark plugs sit vertical and the middle plug has a small pool of water underneath it that drips every so often. Enough water drips out to notice. I pulled the spark plug out, dried everything off and put the plug back in, started the motor, and the leak appeared again after a few seconds. I pulled the plug wire off of the plug and the motor started missing and running bad, so I know the plug is firing. The plug doesn't show water on it when I pull it out, at least I think it's fuel that is on it. My question is:

If the water is coming out of the cylinder, wouldn't it foul the plug?
If I have the spark plug tight, shouldn't it prevent water from going in or out of motor? HELP

Re: 1977 Merc 70hp LEAK

The water is coming out of a leak in the gasket between the outer cover plate and the inner sparkplug boss on the cylinder casting. It's not getting into the cylinder. Keep an eye oon it and see if it gets worse or better. The leak will either enlarge of lime shut. The gasket isn't expensive, but you have to chisel them off the surfaces and that can do more harm than good. See if it just limes shut in a few runs before doing the gasket.

The leak usually starts from an overheat warping the surfaces and overheating the gasket. You should look into servicing the water pump.

Re: 1977 Merc 70hp LEAK

Willy, that is some fantastic news. I was really hoping that the leak was coming out of a water jacket or something. I replaced the following on the motor: Complete Impeller including housings, trigger-wire assembly, prop serviced, spark plugs, lower unit gear oil, and I think that's it. Not to mention I rebuilt the transom with Nida-Bond pourable transom. Now my 16ft 1969 MFG Westfield might be ready to sail again. Can you think of anything else I should do? It sat for a couple years, but nice little boat.

Re: 1977 Merc 70hp LEAK

Tell me more about this Pourable Transom.

Re: 1977 Merc 70hp LEAK

Heres the product website. I have a forum piece on www.fiberglassics.com complete with pictures but I can't get the website to load once I log in. It is some fantastic stuff. 300 bucks and some elbow grease and I have a brand new transom. Didn't have to cut the boat up nor do a bunch of glassing work.

http://www.nida-core.com/english/nordprod_nidabond_transom.htm