1979 Mercury 7.5 Crankcase Vent

Pripyat

Cadet
Joined
Mar 6, 2017
Messages
19
I cleaned everything up today. No wonder there were cooling issues.. the gaskets expanded and were blocking flow.

While I have this thing torn apart - should I inspect that cylinder/piston? I noticed it didn't look quite right. I have honed cylinders but that is all I'm able to do myself. I have plastigauge and assembly lube as well.

I noticed an odd sound at WOT while at the lake the other day. Reminded me of someone slapping two 2x4s together (on the flat side). Sharp, clean smacking sound. Not sure what it could be. Only heard at WOT.
 

Pripyat

Cadet
Joined
Mar 6, 2017
Messages
19
I'm looking for recommendations on how to proceed - how long will this engine operate before it catastrophically fails? Can I just hone and reassemble and expect it to last another 50 hours?Should I be looking for a new block?

New rings are $50 - I can get an entire running 9.8 for $100 off CL. Having this one machined doesn't make sense considering the age and lack of availability of parts. If it were a 9.9, maybe.
 

jimmbo

Supreme Mariner
Joined
May 24, 2004
Messages
12,944
You are going to need new pistons. Cylinders can be bored oversize. What do the bearing surfaces for the con rods on the crank look like?
Water jackets looks horrible, what kind of water was it run in, salt?

It will cost more than $100 to fix your engine, even if you just hone and replace the rings. It would run for a while. How long? Who knows. Of course if and when it does fail, it will be at least 8 miles from shore, just before dusk, and with a huge storm heading your way

Myself, I would hone it, remove any high spots on the pistons, re ring, and reseal it, and then run it. Never going further than a reasonable rowing distance from home. But I would just want see how long it would last.

For $100 you can buy another potential set of problems, but it might be a good buy
 
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jimmbo

Supreme Mariner
Joined
May 24, 2004
Messages
12,944
Where do you find O/S pistons and rings for these models ?

I guess I was mistaken, as it appears there are no O/S pistons available for this engine. In fact even finding std pistons was a chore. Well it is almost 40 yrs old
 

Pripyat

Cadet
Joined
Mar 6, 2017
Messages
19
I may dabble with this engine some more but am debating just parting it out on ebay to recoup some of my expenses.

Can you guys recommend a popular engine that was made for a long period of time, is robust, and parts are still available? I may just try to pick up a new project engine off CL. I've enjoyed working on the Mercury but it looks like it isn't worth fixing (sourcing a new block).
 
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