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Narrow Down Source of Noise in 1990 OMC Cobra Outdrive

B

BigBN

New member
Hi All,

1990 FourWInns 20' with OMC Cobra model #986702 and 5.7 engine.

Outdrive has loud noise when either idling or in gear. Almost seems like a really loud rattling/banging. Noise seems up at the top of the outdrive. Most likely culprit is gimbal bearing and/or alignment? (that is what others tell me and what I read).

Clues:

1. Pulling the outdrive went well until it was free of the bolts, then it didn't want to come out (the drive shaft seemed "stuck" inside). Eventually got it pulled free but took some force.

2. Ujoints and shaft look good - no obvious issues.

3. Ujoint bellows and gimbal bearing were free from water or other materials - they looked good - but many years of greasing through the zirk at winterization time had built up a LOT of grease in there in front of and behind the gimbal bearing and grease seal. This tells me the outdrive hasn't been pulled in a long time.

4. After I pulled the outdrive and ran the engine - the noise was gone.

As a relative newbie, I am not sure how to adequately inspect the gimbal bearing to tell if it is the problem. Would love suggestions on how to do so. Note: gimbal bearing turns smoothly and seems to have no play I can feel. What are suggestions to help me decide if the GB is really the problem?

Finally, I plan on checking alignment as soon as the tool comes - I know that is a big part of this as well.

Thanks,

BigBN

p.s. Love the forum - so many good people answering questions here - thanks! I hope I can contribute in the future,
 
Do a visual inspection (as best as possible) of the coupler splines. They should be square not tapered to a point. Basically they look like the splines of the drive shaft. If worn, then most likely out of alignment. The coupler splines are aluminum so virtually all the wear is on the coupler not the shaft.
 
The gimble bearing should rotate very smoothly when turned with your finger.
U joints can fool you, is there any sign of rust coming from the rubber seals? Sometimes wear is not apparent until they are taken apart. I replaced the gimble in mine about 20 years ago and the U joints are the same ones on the boat from when I bought it, back in 2002. If the gimble is smooth and the u joints look good when you take them apart, my next thing to check would be to remove the bottom drain plug from the outdrive briefly see if there are big chunks sticking to it. You can also (if the bolts come out) remove the top cover to inspect the upper gears.
PS we have similar boats, mine's a couple years older and has a 4.3 V6 4bbl instead of the V8. Same Cobra drive all these years. It has not needed a lot of repairs, the last 2 I did was rebuilding both trim rams (but they were 36 years old at the time!) and replacing the seal on the impeller mount, this is a common point for water to get in the gear oil.
2023 end of season.jpg

Here's mine, used in salt water all this time, it's still a nice riding boat.
 
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