Merc 140: Sudden RPM Drop, Rough Idle, Engine Shake

If it’s a 1974 engine you might think about biting the bullet and getting a crate engine.

Good luck! Keep us posted.
 
no compression in two cylinders ? Before you pull the head, suggest you pull the valve cover, spin the motor, and see if all the valves are moving,
 
alk, yes! I see the Edit option now. Great idea on checking valve motion. The heavy Canada wildfire smoke is finally clearing out of Wisconsin, so when the temps get a little cooler I'm going to try that.

Walshie, I think a crate engine will cost more than the whole boat is worth. It's a 1974 Harris FloteBote that we've refurbished, with extruded aluminum floor and nice furniture, and it's now 32' long x 8'6" wide, but it's still a work in progress (a permanent state of affairs, I'm afraid).

Thanks.

Steve
 
Sorry so late updating this. Been super busy with work, building a deck, etc, etc.

It was a blown head gasket. I did the repair myself last August (2023). I watched several videos, then took my time following the Mercruiser Service Manual. It was a great learning experience. The 1974 Merc 140 runs well now.

Thanks for everyone's advice.

Steve

merc140-1b.jpg

merc140-2b.jpg
 
Thanks for the follow-up, glad it all worked out. The cylinders look nice and clean, you should get plenty more hours out of it.
 
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