Vibration

[wyocobra]

I have a '87 Baja Sunsport that has a 5.7L OMC Cobra I/O. I purchased the boat last summer from the original owner and he claimed it only had 80-90 hours total since new. Judging by the condition of everything, I don't think he was far off. Anyway, since I've owned the boat it has had a vibration when turning or if the drive is trimmed up. I assumed the problem was bad u-joints. Well, yesterday I pulled the vertival drive off and the u-joints look like they were just replaced. They move freely and have plenty of grease. I have an original OMC service manual, but don't see anything obvious other than the u-joints that could cause the vibration. The gimbal bearing was well greased and seemed be in excellent condition. This is my first boat and I'm still learning, though, so is there another component that could be causing the vibration? Any help would be greatly appreciated!

 

[jtmarten]

Re: Vibration

Pull the prop and run it on the muffs. Most likely the prop is out of balance or has a bad hub.
It could still be the u-joints as well. They're hard to diagnose statically.

 

[wyocobra]

Re: Vibration

Thanks for the reply. I forgot to mention that the vibration is there while revving the engine in neutral, too. I also swapped out the prop last year and nothing changed. I suppose I should probably replace the u-joints anyway. I'm still doubtful that's the cause, though. I would suspect something might be out of balance or bent, but it runs nice and smooth when going straight. It really only starts to vibrate when turning fairly hard. That's not just a normal thing for this old drive, is it?

 

[jtmarten]

Re: Vibration

Not normal. Could be the gimbal bearing or the u-joints. Any grit at all when rotating the bearing?

 

[bds85466]

Re: Vibration

I'm only saying this because I just found out mine isn't: Is your motor mounted tight?

 

[wyocobra]

Re: Vibration

The gimbal bearing is smooth as silk and has plenty of grease. I didn't think about loose motor mounts, but I could see how that might cause my vibration. I thought I checked them when I bought the boat, but it would be worth looking again. Thanks again for all the help. I'll probably replace the u-joints anyway because I'm sure they're not too expensive and I already have it apart. Hopefully that and checking the mounts with a torque wrench fixes the problem.

This might be a really stupid question, but it couldn't have anything to do with the water pump, could it? The engine runs at about 160 degrees and I think someone removed the thermostat. I was planning on replacing the impeller and thermostat. There's obviously a problem somewhere in the cooling system. I was just thinking though, isn't the water pump driven off of the driveshaft?