1984 MCM 470 3.7l Big problems!

mshiff62

Seaman Apprentice
Joined
Jul 5, 2013
Messages
36
1984 Mercruiser 470 3.7L.

So I had big hopes of boating all weekend. That went out the window fast. I put it in the water, started it up, the oil pressure was at 80psi, and it was idling extemely low about 300rpm, pushed the throttle wide open and nothing changed, in which it then choked out. I got it to restart but it was making some clanging noises and running really rough. I put it in gear and barely atared moving, maybe at 800 rpm, and I looked back and smoke is rolling out of the motor. I was able to nurse it back, in which as soon as I tried to give it throttle it was smoking like crazy and oil pressure was at about 30psi, occasionally it would stall out. So on the trailer It went.

So, here is what I have tested/observed so far.

-oil all around valve cover, in flame arrestor, carb, and on head.
-spark plugs were solid black, not wet/oil
-pulled valve cover, very minimal oil, springs, rockers, rods all looked ok.
-turned over engine with no spark plugs, no oil coming out of cylinders.

That is all I can look at right now as I'm on vacation so my fiancee doesn't want me spending all weekend working on it. Any and all suggestions are apreciated and anyone who has experiance with these motors especially. Thanks!
 
Joined
Mar 27, 2010
Messages
3,008
What's the history on annual maintenance on it? the engine and drive, not the boat lol

timing at?
point gap/dwell at?

Was it running good on the trailer and now bad in the water or something else?
 

Bt Doctur

Supreme Mariner
Joined
Aug 29, 2004
Messages
19,093
Tell us the Truth, the whole Truth and nothing but the Truth

So you went to the boat, pulled the motor box, checked all the items that needed checking,
started the motor, let it warm up then left the dock?
What is the oil level? black smoke is indicative of a choke issue
 
Last edited:

mshiff62

Seaman Apprentice
Joined
Jul 5, 2013
Messages
36
I bought the boat used 2 years ago, so as long as I have had it, it has been taken care of. As far as timing and point/gap dwell I have no idea, how to even check them. And yes a few days ago I had the muffs on it and it ran fine, as soon as I started it in the water the oil pressure was at 80 and it was barely running. The oil level is right at full, not overfull. And it was not black smoke, it was white smoke.
 

Bt Doctur

Supreme Mariner
Joined
Aug 29, 2004
Messages
19,093
heavy white smoke could be the A/F burning off. was it ever overheated? possible blown head gasket?
would need to hole a piston to blow out that much oil. compression test should be next.
 

mshiff62

Seaman Apprentice
Joined
Jul 5, 2013
Messages
36
I have never seen it get over 160 degrees, and it was still full of coolant. I will compression test it witg a gauge on monday, but just putting my thumb over the holes and turning it over they all felt the same.
 

stonyloam

Vice Admiral
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Mar 13, 2009
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5,827
Yeah, compression test is number one. When was the impeller last changed?
 

mshiff62

Seaman Apprentice
Joined
Jul 5, 2013
Messages
36
I have not changed the impeller, I was told it was done right before I bought it. I am not too sure how to do that with an outdrive. And would that affect it in my situation? When I started it on the trailer it was peeing out water so I assumed it was working.
 
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