1992 Mercruiser 4.3 Alpha 1 Gen 2 Motor Knocking Noise

[nic420]

Bayliner 2252 Classic has been sitting since 1992 and the motor was frozen / stuck when I bought it. Got it to run and took it out. When at 3500 RPM the motor made a knocking noise, smoked, overheated, and shut off. Wouldn't start again until motor cooled. The knocking sounded like it's coming from the front of the motor on the port side. Got towed by BoatASS.

Started the motor at home ran smooth. Rebuilt the cooling system runs smooth and cool. Took it out fishing w/ the kids and ran cool for a while until the knocking sound again. Engine overheated and shut off like before and wouldn't start. Waited for motor to cool and started it. This time drove slow to make it home w/o having to call BoatASS. At low speed it started to make the the same knocking sound again but this time way louder. Drove for a mile with the noise toward the launch and then the motor died w/ low temperature. Tried to start the motor again but this time no start. Sounds like no compression at all. Got towed in.

Don't know where to start. Could it be the timing chain finally broke? Please advise how to troubleshoot. Thank you for your time.

 

[dubs283]

need to check compression, sounds like and actually checking are two different things

you revived a motor from a locked up state that had been sitting for 28 years, you are fortunate to have gotten the few hours you did with it

 

[Scott Danforth]

not the timing chain.

first thing to start with is pull the drive, then pull the motor. you have a tear down to do.

 

[nic420]

Removed the plugs, Belts, and pulleys today. Hand turned / cranked the motor and did not hear any noise.

 

[nic420]

Took off the port valve cover today and they all look good.

 

[Scott Danforth]

Your issue will be bearings. You cant take a motor that was stuck for many years and expect it to be OK. The acid buildup alone in the oil would have destroyed the bearings.

Pull the motor, get it on an engine stand, and start a tear down

 

[nic420]

Aye aye Captain! Was hoping it might be the timing chain. LOL.

 

[nic420]

Updates. Tore the block apart and it was the #1 crankshaft bearing that was busted, blown head gasket on the starboard bank, and water in # 4 & 6 cylinder.

Brought the block core and the heads to a machine shop for hot tank, boring, and cleaning.

Trying to get parts together for the rebuild and don't know what pistons kit to buy or what parts should be replace. Please advise.

 

[Rick Stephens]

Your machinist will supply those parts. Should be turning the crank as well. You might even consider just getting the entire rotational assembly as one balanced set.

 

[nic420]

On the fly wheel, there are 3 bolts that are used to fasten the 3 triangular shaped plates. I was not able to remove one of them per it was rusted and had to cut of the bolt. I am trying to find out from the forum if I need those triangular pieces when i do the re-install? I was also trying to find the replacements but don't see them in the engine diagram.

 

[nic420]

Just found out those 3 triangular plates are part of the coupling assembly. Can I mount the coupling assembly to the flywheel different from its original position? I noticed there are other holes on the flywheel.

 

[nic420]

Please disregard the prior question. Please advise where I can buy just the triangular plates w/o having to buy the whole coupling assembly?

 

[Rick Stephens]

Please disregard the prior question. Please advise where I can buy just the triangular plates w/o having to buy the whole coupling assembly?

Interesting question. Not a listed or shown item.

 

[nic420]

Found the part, thank you. The oil pump pick up opening (5/8) that came w/ the master rebuild kit is too big for my original oil pump pick up strainer. What can I do to snug it up? JB Weld?

 

[nic420]

I can't seem to reinstall the original harmonic balance back no matter what tool I have tried. Does anybody have any other tricks?

 

[nola mike]

What's the issue/you've tried a balancer install tool?