Mercruiser 4.3 slips and stops

[shagtimetim]

I need help ASAP. I have a Mercruiser 4.3 lx i/o which has been running this season with no problem. We were in semi rough waters of a lake when I was going about 20 mph. My boat suddenly increses RPMs and stops forward momentum. I shut it down, looked in engine compartment and at prop with no evidence of problems. Started it back up and boat would forward at idle speed. I then began smelling what seemed to be a rubber burning, but again found no evidence of a problem. I sat for appx. 1.5 hrs hoping it was an overheat problem. WHen I started back up there was an awful vibration, but the boat would go forward at idle. About 100 yards from shore, the motor then started over heating severely. Any ideas? I did have big July 4th plans!

 

[Bt Doctur]

Re: Mercruiser 4.3 slips and stops

Coupler is bad, the rubber smell and the overheat are the clues.
Coupler failure is mostly caused by mis-alignment ,usually from bad/ loose motor mounts.You can check this by putting the key in your pocket, shift into full fwd gear, have someone watch the shaft where it enters the back of the motor, and you stand on a prop blade trying to turn it.
prop moves, shaft moves= coupler bad
prop moves, shaft dosent= drive issue

 

[Fun Times]

Re: Mercruiser 4.3 slips and stops

I need help ASAP. I have a Mercruiser 4.3 lx i/o which has been running this season with no problem. We were in semi rough waters of a lake when I was going about 20 mph. My boat suddenly increses RPMs and stops forward momentum. I shut it down, looked in engine compartment and at prop with no evidence of problems. Started it back up and boat would forward at idle speed. I then began smelling what seemed to be a rubber burning, but again found no evidence of a problem. I sat for appx. 1.5 hrs hoping it was an overheat problem. WHen I started back up there was an awful vibration, but the boat would go forward at idle. About 100 yards from shore, the motor then started over heating severely. Any ideas? I did have big July 4th plans!

You may have burned the rubber up inside the engine coupler, And maybe because it is A alpha drive the impeller that is between the upper and lower unit in the stern drive was not turning the impeller at the needed speed to keep the engine cool b/c of the engine coupler was slipping.

 

[shagtimetim]

Re: Mercruiser 4.3 slips and stops

I'm not certain what you mean by watching the shaft move. The prop will move in either direction depending on whether you are in forward or reverse, and will not budge in the other direction. I spoke with a local mechanic, and he seems to think coupler as well. I was also told this requires engine removal and so on. I am a hobby mechanic, but my background consist of VW rail buggy building, etc.. I also rebuild VW engines. However, I'm not sure this is something I can tackle. The fright comes with aligning the engine etc.. I have been quoted 1500.00 to replace the coupler. Any advise? Also, is there like a "Chilton's" manual to perform this type of thing? Thanks very much for your help!