Please help me track down vibration

[petedw]

I have a 1979 mercruiser 140 which has a bad vibration. Almost a thumping. I changed the gimbal bearing and the u-joints seem fine. I used the alignment tool. The vibration is still there. So I took off the outdrive and still feel it. It looks like there could be cracks in the coupler and if I take out the gimbal bearing and stick the alignment tool in I can move it around with little force. So. Can the coupler be cracked and have play in it without completely breaking? If it is going bad would this cause vibration even without the outdrive connected? I am assuming this is the problem, but don't want to pull the engine out if it's not the problem. However, you cannot see it very well. Thanks for any help.

 

[petedw]

Re: Please help me track down vibration

I am actually wondering if it is the coupler.

 

[daydreamer1252]

Re: Please help me track down vibration

It would take a monsterously bad coupler to cause the vibration with the outdrive removed....at that point it is not connected or "touching" anything.....just sort of spinning in space....does the boat move in the water?......does it apply power to the water normally? Again I doubt a coupler bad enough to cause your issue would transfer power.....Another thought....is the coupler physically loose as in wobbling around??

Good hunting....

 

[petedw]

Re: Please help me track down vibration

It does not feel like it is wobbling, but does look like it might have cracks in it and I can move it around pretty easily with the alignment tool and it almost feels like it may not go back to the center. The engine seems to be running fine and the mounts seem solid, so are is there anything else to look into?

 

[ziggy]

Re: Please help me track down vibration

so are is there anything else to look into?

the compression test that was refered to in post #2

 

[Don S]

Re: Please help me track down vibration

The engine seems to be running fine

I had a boat come in where the customer complained about it lacking power, he also said , and I quote. "It runs great"
I started it up and it had a horrible miss. Turn out, he had no compression on 2 cylinders. He adjusted the valves improperly.

Bubba mentioned a compression test, and I agree, I would also (with the engine running) remove one plug wire at a time and see if it causes the engine rpm to drop. No drop, that cylinder is not doing anything.

But, if all you want to hear is about your coupler, here goes.

I would pull the engine and replace the coupler and see if the vibration goes away.

There, now I've said what you want to hear.

 

[petedw]

Re: Please help me track down vibration

Thanks for the response. So it is possible that there is something going on in the engine itself that would cause a vibration even if the engine seems to be running fine. It even runs fine on the water. Thanks. I guess I will give the compression a shot just in case.

 

[ziggy]

Re: Please help me track down vibration

I guess I will give the compression a shot just in case.

might as well. besides. it's a good idea to do a compression test anyways. i perform 2 a year on my boat. one in spring, one in fall. it's just something to compare too if something goes wrong. i at least know where i stood compression wise prior to a possible problem. it also lets me know my engine's general health.