MerCruiser 888: Coupler - Damaged?

[eldplanko]

I was hoping to get some feedback to determine whether the coupler is damaged on my Mercruiser 888 (1974, Ford 302).

As background, I purchased the boat ~2 months ago. The previous owner had stated that previously, the coupler had failed due to a stringer failure (due to rot) under the front engine mount. The previous owner stated he pulled the engine / outdrive, stripped all rotted wood, reglassed, and remounted the engine / sterndrive. He also stated he reinstalled with a used coupler. As far as I can tell, he also reused the front and rear engine mounts. And the stringers and mounts are sound.

When I took this boat out, the engine / outrdive operated without incident under low power (idle to ~1500 rpm) in the water. When I opened the engine up to full power, I head a noise indicating major drive failure, immediatley shut down, and returned to dock with the trolling motor. I pulled the outdrive, and upon inspection there was a failure in both the U-joint (one bearing cup came off of the spider and was loose in the U-joint bellows so that the spider was free to move freely in the yolk), and the gimbal bearing (inner race spit in half and loose in the U-joint bellows, ball bearings loose in the U-joint bellows). I suspect these components were weakened by the previous coupler failure, and failed when I took it to full power.

Upon further inspection, the U-joint yolks and shaft, bell housing, gimbal housing and gimbal ring were not damaged. I pulled the remains of the damaged gimbal bearing and pressed on a new one. When I checked the alignment with the alignment tool I found:

1. I needed to raise the engine ~1 inch for the tool to slide into the engine coupler with no resistance. I suspect the previous owner did not correctly align the engine after the engine mount stringer failure.

2. If I rotate the crankshaft 180-degrees from the where the tool effortlessly enters the coupler with no resistance (i.e. 0-degrees), the tool will only enter the coupler half-ways (~1 inch) before meeting resistance. Also, if slide the tool into the shaft at 0-degrees (no resistance), rotate the crankshaft 180-degrees with the tool in the coupler, it is extremely difficult (but not impossible) to remove the tool

I suspect this means the coupler is damaged, such that the coupler (more specifically, the female splined shaft inside the coupler) is not parellel and centered to the crankshaft. Does this sound correct, or could this be a result of incorrect engine alignment? I'd like to rule that out before I pull the engine.

Any and all comments or suggestions are appreciated.

 

[racinrc14]

Re: MerCruiser 888: Coupler - Damaged?

The coupler's construction is such that the inner 'female' part is isolated, in rubber, from the outer housing. I find it difficult to believe that the coupler inner is mis-aligned from the outer. Usually, couplers fail by spinning the inner within the outer resulting in loss of drive and a burnt rubber smell in the bilge. I suppose it could happen, though. Either way, your alignment is not correct for the whole 360', and providing everything else (gimbal bearing, alignment tool, etc) is straight and true, that leaves the coupler. And that means the engine has to come out to replace it. It goes without saying that this 'wobble' is probably what trashed your u-joint and bearing.

 

[eldplanko]

Re: MerCruiser 888: Coupler - Damaged?

Thanks for your reply. I was definitly thinking something similar.

I'm assuming the gimbal bearing retainer is fully seated (it seems to be). Also, in all cases the alignment too can begin to enter the coupler, which suggests that at least the front of the coupler is aligned with with the gimbal bearing. So it seems the only explanation for what I've described is a problem with the coupler. I just want to make sure I'm not missing something with the alignment before I pull the engine.

 

[racinrc14]

Re: MerCruiser 888: Coupler - Damaged?

Even if the bearing isn't fully seated, the inner race can 'swivel' some. I reckon that if the inner race is not centered inline with the output from the coupler, while the alignment bar is in, it might show a 'wobble', but that would mean your alignment bar is too small in diameter, allowing the bearing to sit ****-eyed on it. Highly unlikely. Have you double checked the straightness of your bar? Even if it has only a few thousandths runout it can affect the way the alignment is read. Might save from having to pull that motor.....

 

[eldplanko]

Re: MerCruiser 888: Coupler - Damaged?

Thanks for the suggestion. The fit between the alignment bar and the gimbal bearing seems correct (i.e. no play). I'm unsure of the alignment bar run-out though. The best I can do is check it with a micrometer, as I don't have anything to mount it on and rotate to check the run-out with a dial (the space between the transom and engine coupler is a little tight to do this properly ).

I'm open to anyone else's suggesions or comments. Thanks for your help.