95 5.7 mercruiser engine advice

[95VIP]

I recently took my 95 VIP to the shop to have them look at it. When i would try to start it , it would back fire through the carb and exhaust. The shop said he did a compression test and cylinders 8 has no compression and 6 has only 30%. The spark plug i pulled out of cylinder 8 was completely missing the top of the hole plug. He told me to pull the head on that side and see if the head gasket is blown and replace. But when i bought the boat the previous owner said his mechanic said it had a spun bearing. What should I do? Please, any advice will help.

 

[boatguya1]

Re: 95 5.7 mercruiser engine advice

If you have any confidence in the old owners mechanic I'd build/replace the motor.

Couldn't hurt to pull the head and look. If you find piston/cylinder damage then it's a no brainer. My guess is you will find some kind of valve problem then you will have choices to make. You won't see a spun brg and there is no sense doing valves on a motor with one. On the other hand who knows if the other guy knows what he's talking about.

James

 

[TilliamWe]

Re: 95 5.7 mercruiser engine advice

You've at least got valve issues. Headgasket has nothing to do with these symptoms. It's the valves. Your shop guy ain't real bright. But he's right about one thing, the heads need to come off, at least to confirm you don't have a hole in #8 piston.
Motor was "lugged" for a long period of time, by the previous owner, would be my first guess.