Mercruiser Ford 302 blow-by

I just purchased a 1975 trisonic with a ford 302 in it. The guy I bought it from said it ran fine 2 summers ago. He said he never winterized it and this past summer it had a cracked manifold which he replaced. When he started it up for the first time he said it had bad blow by and smoke and oil was coming out the valve cover. He said it ran and sound good it just had a loss in power. He said he thinks its a stuck ring. Does anyone else have any idea of what could be the problem. I have not looked into it at all myself. I have not picked it up yet.

 

If a manifold cracked; it's definitely possible the block and/or the heads weren't drained and cracked as well. If it's turning over, I don't know what he means by a stuck ring - stuck valve? I couldn't imagine how an engine spewing smoke and oil from the valve cover could be described as running good. Did this just start after the winter he didn't winterize?
Are you hooking it up to water when you start it? How does the oil look?

 

If he replaced the manifolds he know what is wrong with it or knows there is a problem with it. Serious blow back like that is more than a stuck ring. It could have been stuck at one time as the water from the cracked manifold seeped into the cylinders.

If the oil pressure is good then you may get away with a re bore, certainly a strip down. Isnt it cheaper in US to buy a short motor?

To value the boat you need to consider the engine un useable.

 

well I paid close to nothing for the boat. Basically I just want to get it running decent. I would be happy if it only lasts for one summer. Im not going to put a lot of money into it. I have not looked at it closely or ran it or seen it run. Im just repeating what the guy told me. He said it ran good for a season and these problems came after the winter that it was not winterized. I think he said the first time he started it after the winter he noticed water leaking from the manifold so he replaced that. He said he noticed it had some blow by but he figured it needed to be run so he took it out on the water and he said it never got better. He said the boat would get up on plane but that was it. I asked if it was knocking or anything and he said it was not. He said it sounded good. I think that was the last time he used it. He said he winterized it this winter. Im just hoping this will be a somewhat easy fix. I already planned on having to pull the motor, Im just hoping I can get by with replacing the rings and gaskets. But like I say I dont know anything more than what he told me. Im picking it up this weekend and I will examine it closer and as soon as it gets warmer I will start it up and see for myself exactly what its doing. Thanks for the replys so far.

 

The 302 explorer motor from 97 till whenever they discontinued it is a good choice if you have to replace your motor. I've seen these complete with under 75K miles for under $500. You'd have to pull all the fuel injection components and intake manifold then put all the accessories from your marine motor on it; but it'd be something to look into.

Pardon my ignorance; but what's a stuck ring? Stuck in the groove of the piston and not making contact with the cylinder wall? hence the blow-by.

 

Yes, thats what a stuck ring is.

 

Update:
Well it finally warmed up here and I got a chance to work on it. I pulled the tanks out and cleaned them, drained the oil which looked good, just dirty, and pulled the plugs which were oil and gas fouled. I tried to do a compression test and when I cranked the engine over, oil shot out of 3 or 4 of the spark plug holes. I didnt get more than about 30-40psi on the 2 cylinders I checked. I figured I would need to pull the motor either way. So I pulled it on saturday and tore it down yesterday. Half of the pistons had oil sitting on top of them. I did notice that one intake valve had a crack/chip in the side of it. Other than that I didnt see anything else that was obviously wrong. The cylinders looked good, the pistons looked ok, and the crank looked ok and spun smoothly. The flywheel was slightly bent though. I talked to a guy who knows engines and he said it would just need some head work, a new valve, and a minor engine rebuild (piston rings, gastkets)and get the flywheel straightened. I never actually tried to start the engine before I pulled it. I dont know how it could have run with all that oil getting by the pistons. the boat says it only has 480hrs but Im not positive that the hour meter works. Is there anything else I should be checking or be worried about. This is the first time I have ever messed with a boat engine so I am new to all this. Also a lot of the water ports were rusted and corroded. What should I do about that? Does anyone know where I can get a service manual for this engine? Thanks!