Noise in 4.3

[firecapt13]

Changed the prop and carried it out today. It started making noises like knocking or clanging. I thought it may be the exhaust flappers because the noise was not constant. It got progressively worse and boat quit running. I havent worked on it yet but it appears to be hydrolocked.

Will leaking water from manifold or riser cause a knock in motor. It sounded like a valve knock.

I took a video for you to hear that may help but i cant load it

1992 Mercruiser 4.3

 

[Bt Doctur]

Re: Noise in 4.3

Or the drive ran out of oil. Pull the drive to isolate the trouble.

 

[firecapt13]

Re: Noise in 4.3

I did try to isolate the noise before boat left me in middle of lake during storm. It appeared to be coming from 135 side of engine. The oil on dipstick looks like new and it is at correct level.

The good news is that the vibration i was trying to diagnose in another thread went away with new prop. Boat ran good except for the knocking, until it quit

 

[Bt Doctur]

Re: Noise in 4.3

Not being there at that moment ,it`s hard to give the answer. Noise can travel ,so remove the drive first, then the spark plugs to see if any water comes out. If still locked, pull the heads.

 

[firecapt13]

Re: Noise in 4.3

Update

I removed the drive and noise was definatily in engine. I pulled it out and found a spun rod bearing on the #1 piston. It quit running because plug on thunderbolt slipped out, go figure.

There was no water in the cylinders or oil just parts of bearing.

The boat did suck water in once while i was trying to get it running and adjust the valves i removed the riser and gasket was broken and got water in. I then pulled plugs and cleaned out cylinders and it ran good.

What are some causes of spun bearing on fresh rebuild. I replaced all bearings and rings.

What is a proper break in for a boat motor?

 

[Anchor Management 1]

Re: Noise in 4.3

Whas the crank chamfered (good) on that cyl?