Old Merc Problems

[Goldwinder]

Hey everyone. I'm new to the forum and just bought my first boat. It's a 1973 Sidewinder with a Merc 120 I/O that is/was in great shape...or so I thought. I took it to a local mechanic to have the outdrive resealed and impeller changed. When he finished that he put it on the water to test it and it overheated almost immediately at WOT. He subsequently had the heads redecked because of some blow-by supposedly but now he has found that the exh manifold is cracked. Because of the age I haven't been able to find a used manifold that isn't also cracked and a new one is $300. In the meantime we've found a recently rebuilt Merc 140 for sale for $400. He is trying to talk me into doing an engine swap since the costs are so close and he says mine will need piston work and new rings very soon anyway.

I'm hesitant to do this since my engine ran fine the last time I had it out a few weeks ago and you just never know what you get when you buy a used motor off something like craigslist. Although I would like the extra 20hp and it does make sense to me to spend a little extra if the newer motor is in better condition than mine.

Any advice or thoughts from all of you with much more boating experience than me will be very much appreciated. Also, I was wondering if when the mechanic overheated it and poured water on it to cool it off while idling back to the dock might have caused the manifold to crack. Thanks for any help!

 

[Windykid]

Re: Old Merc Problems

How about posting the compression readings?

 

[Goldwinder]

Re: Old Merc Problems

He told me compression in 3 of the cylinders was 135 but the #2, I believe, was down a little - around 120. That is why he had the heads redecked. He said they shaved 5 thousandths off to get it back flat.

I think these comp numbers are right but can't remember exactly. But he did tell me that 3 of the 4 were good and just the one was low.