4.3L OMC Cobra 1988 engine knock/rattle

[Ron_beemer]

Hey all. I picked up this boat. I am new to the scene. It starts up great but has this knocking / rattle it's very defined at idol but goes away with rpm's. It sounds like it's coming from the back by the transom.
Check out this video.

 

[Bondo]

Ayuh,...... Welcome Aboard,...... Pull the drive, 'n try it, to see whether it's the motor or drive,....

 

[stresspoint]

i recon it may be an exhaust flapper. just a guess and an easy examination.

 

[Ron_beemer]

Exhaust flappers are okay. Ordered a new gimbal bearing in hopes it could be this and will be pull the drive then to find out... Will keep you posted. Any other suggestions?

 

[Bondo]

Exhaust flappers are okay. Ordered a new gimbal bearing in hopes it could be this and will be pull the drive then to find out... Will keep you posted. Any other suggestions?

Ayuh,.....The drive turns with the motor,...
Pull the drive, 'n try it to see if the sound stops, or not,....

 

[Lou C]

Exactly if you pull the drive & it’s quiet it could be a REALLY rusted gimble bearing or someone might have refilled the Cobra drive the wrong way and trashed the upper gear housing. Hopefully it’s the former not the latter

 

[Ron_beemer]

Well with the drive pulled the noise still prevails unfortunately. So it looks like we're going to be pulling the engine, flipping her over and pulling the pan and hopefully find something we can fix quite quickly without having to replace too many parts. After pulling a good sample of the oil as well, noticed it was slightly milky so I will be doing the head gasket and manifold gaskets. After a compression test, all cylinders seem to hold compression.

 

[Ron_beemer]

Problem solved. Pulled engine and had super loose bolts on fly wheel.

 

[Ron_beemer]

When running bilge is taking on water. Hmm next problem lol

 

[kenny nunez]

Does water come in when the boat is in the water without the engine running?

 

[Ron_beemer]

Found the leak well as far as I can tell without being in the water. Power steering cooler spraying everywhere.

 

[Bondo]

Found the leak well as far as I can tell without being in the water. Power steering cooler spraying everywhere.

Ayuh,..... Probably frozen, 'n busted,.....

Don't run it without the cooler, or you'll burn up the pump,...

 

[Lou C]

Those have a drain plug on em but it’s nearly impossible to get at, all you have to do to keep ‘em from freezing is put the drive down, disconnect the raw water intake hose at the thermostat housing & point it down in the bilge to drain. Then hold it up & fill it with -100 marine antifreeze till you see AF coming out the water intakes, this will push out all the water. I’ve been doing this for years & no freeze ups even down to 0 degrees F.

 

[Ron_beemer]

Well I took her out and had great success!

 

[Bondo]

Well I took her out and had great success!

Ayuh,..... So where, 'n why was it spewin' water,..??

 

[Lou C]

P/S cooler seemed to be the problem, make sure to drain the hose leading to it (hold it down in the bilge to drain) then hold it up, and fill with marine AF to push out the water (with drive down) till AF comes out your outdrive water intakes.