OMC cobra outdrive rattle

[decker307]

Hello all,

I have a 1991 Four Winns with the 4.3 V6. The motor has 102 original hours on it and runs like a top. It has an OMC outdrive that has developed a strange sound.

While out on the water over the 4th, I noticed a rattle that got worse the further up I trimmed it. I couldn't hear the rattle when the prop was below the water line. If its trimmed all the way up, and the engine is at idle, the noise isn't present. It only rattles when I throttle up a bit.

I took it out of the water and brought the boat home. I hooked it up to the muffs and the rattle becomes noticeable when trimmed up about half way. The further I trim it up, the louder the rattle. It seems to be coming from the prop area. I also noticed it rattle slightly when I turn the wheel all the way to one side.

I pulled the drive off and the U-joints seem to be tight. The gimbal bearing is smooth as can be. That was replaced last year.

I did notice where the caps on the U-joint were making contact with the inside of the yolk if I held the shaft all the way up or all the way down. The metal on the yolk was shiny where it was rubbing. I am not sure if this is the problem as the yolk and U-joints turn together.

I did pull the prop off to check for fishing line caught in it. I didnt see anything of concern.

Does anyone have any other ideas on what might be causing this rattle? I appreciate any and all input. Thanks,

Matt

 

[bruceb58]

You shouldn't be running it at all when you have it trimmed up like that.

It's normal for the u-joints to make more noise when trimmed up slightly.

 

[decker307]

Thanks for your reply. I have never heard this rattle before, that is why it concerned me. Should you hear U-joint rattle when trimmed half way up? Can U-joints be bad even when they feel tight when I took them out?

 

[bruceb58]

Yes to both questions. That's why when you run it half way up you should be at idle RPM.

 

[decker307]

Thanks much. I'll be putting new u-joints in this weekend and will keep all this in mind.

 

[bruceb58]

You should post a video of what your rattle sounds like. I would be especially interested in the noise full left and right.

 

[decker307]

I'll hopefully have the new u-joints in this weekend. If it's still making the rattle, I'll take a video of it and post it for you to see/hear.

 

[decker307]

I can't figure out how to upload a video!

 

[decker307]

https://youtu.be/DhTs6YHM86A

Here is a YouTube link to the video.

 

[Thajeffski]

Doesn't sound like typical U JOINT out drive rattle.

The water pump is right behind where you had the camera... maybe something is off in there? If the boat works I'd just use it... and try not to trim up in more then idle.. really shouldn't be giving it much power while trimmed up anyway..

 

[decker307]

How often do the bearings inside the bearing carriers go out? I will check the water pump tomorrow. Looks like I may be off to the marina soon. I don't want to make the problem worse. The out drive oil and gears looked great. Wouldn't that eliminate bearings being bad. I would think my drain plug would have metal shavings if the bearings were going.

 

[bruceb58]

I would never ever run my drive that high in other than idle conditions. I would definitely not rev the engine like that when it was tilted that high.

That would be a normal u-joint noise to me for what you just showed.

As far as bearings in the bearing carrier going out, keep running your drive tilted like that at higher RPMs and you might find out!

 

[decker307]

Well, I ran it yesterday for about 2 hours. Something just doesn't seem right. Rattle is still there. A bit of vibration when turning to either side. Slight turns are fine, but tight turns vibrate. It only vibrates in drive and making tight turns. If I put it in neutral and turn to either side, be there is no vibration. So it's something that has to do with it being in gear. I think I'm going to have my prop redone to see if that helps the vibration. But I don't expect it to do anything for the rattle.

 

[bruceb58]

When was the last time you did an alignment of the gimbal bearing? If that is out of alignment, it would cause the u-joints to knock a little earlier than normal.

 

[decker307]

I haven't ever done an alignment. Honestly, I wouldn't have the first clue how. My Seloc manual explains it, but I believe that's above my capability. I know the few times I've had the outdrive off, when I put it back in, I have to crank the engine quick to get the splines lined up to seat it fully. Otherwise, the drive has about an inch gap and won't seat fully in. I've thought about the alignment, but I haven't had the engine out where it would be out of alignment.

It's very odd to me. The first time I had the boat out this year, all was fine. Then the second time I took it out, this started happening.

 

[bruceb58]

You need to be checking alignment every time you pull the drive. Just the stringers compressing over time will cause an issue. I am almost wondering if your coupler is worn if you haven't ever done an alignment.

Alignment tool is cheap on eBay.

Here are some instructions.

https://dl.dropboxusercontent.com/u/83197541/iboats/Engine Alignment.pdf

 

[Lou C]

Plus if the drive has not been off for service who knows when the last time the U joints were greased? The drive should come off at the end of each season for maintenance--> check bellows for water, gimble and u joints for wear, grease them and the driveshaft splines, and check alignment as noted above. Has this ever been done?

 

[decker307]

I've had the drive off several times. Replaced gimbal bearing and both bellows last year. Just replaced both u joints. I'm somewhat mechanically inclined, and I'm not thinking it's the engine coupler. The boat is a 91 and just rolled over 100 original hours. It runs flawlessly. I will check (or have checked) the alignment to make sure that's not out of whack.