New boat has bad vibration when running

[bheston]

I just purchased a 1989 Four Winns with a 4.3L OMC cobra. I ran it on a hose before I bought it and engine runs great, shifted fine, ran quiet in gear. However once I got it in the water, it has a pretty loud vibration in it, even in neutral. The whole hull of the boat is shaking. It gets worse when the trim is up and when turning, especially when accelerating. Is my gimbal bearing going out? If not what else can cause this?

I plan to replace the gimbal bearing myself if that is the problem, I have read about the alignment tools necessary to do this job. What exactly needs to be aligned, are you aligning the bearing with the drive shaft so it runs evenly in the bearing? Is there a good place to buy these tools? Anything else I should know before tackling this one?

Thanks for the help guys!

 

[Bt Doctur]

Re: New boat has bad vibration when running

you whacked the outdrive trailering it and damaged the prop or shaft
or the U joints are now very loose, but this much play should have shown up on land when shifted into gear or the prop was bent a bit and you never noticed it on land.

 

[bamadave]

Re: New boat has bad vibration when running

How far up are you trimming the outdrive? Does the trim limit work? It almost sounds like you have the outdrive up to far. That severe vibration will only tear things up worse.
If the prop shaft is bent, or the prop bent, you'd see that while on the muffs in gear at idle.

I'm assuming you didn't water test before you bought it?
If not, could be a costly mistake.

 

[bheston]

Re: New boat has bad vibration when running

The prop and prop shaft only spin when in gear don't they? I get the vibration even in neutral, and it changes when I turn left to right. Do you think U-joints? I sure don't recall hitting anything unloading it, I was at a clean ramp.

I'm not trimming the unit up too much, it vibrates with it clear down but seems to get a little worse as you trim up a bit.

 

[Bt Doctur]

Re: New boat has bad vibration when running

Remove the drive and inspect.
remove trim cylinders, remove 6 mounting nuts, pull STRAIGHT BACK, DO NOT LET IT DROP DOWN UNTILL THE SHIFT SHAFT IS CLEAR, otherwise your break the shift cable.
post the results of your findings
I`m betting one or more of the U joint caps are coming out.

 

[bheston]

Re: New boat has bad vibration when running

Well I pulled the lower unit yesterday and found the gimbal bearing is shot. I plan to replace this myself, do I need the bearing install tool and alignment tool or can I get by without them? Anything else I should watch out for with this project? I do have a manual already so I'll read that over a couple times before starting.

 

[PitchFork]

Re: New boat has bad vibration when running

I pulled my bearing on Saturday using the website below. It was pretty easy just a dirty job if it has been greased lately. I was getting growling and vibrations and I found the bearing was shot when I turned the inner race and it was making a noise when I turned it with my fingers while it was still in the boat. It sounds like it has sand in it. I will be calling the boat store this morning to get parts. Bearing, gasket, 2 o-rings for shaft, and 1 o-ring for water pump hole. The hardest part was cutting the outdrive lock off since I bought the boat 2 years ago and did not have the key for it. I also am replacing the six nuts on the outdrive 7/16-20 fine SS coarse locking nuts because they were pretty lose as I could turn them with my hand.

You will need an alignment tool which I am having made at work today since I work for a machine shop with a CNC Lathe and excellent machinists on staff. Make sure you also check the U-Joints and grease them if they are good.

Lots of research and reading has made changing the bearing fairly easy so far.

You are aligning the bearing to the coupler so the outdrive will install. I believe the same website has aligning procedure if the engine needs to be aligned. You can find the tool on eBay for around $70 maybe even cheaper just depends what material they make it out of Stainless or Mild Steel. I am making mine out of Mild Steel and will keep it oiled.

http://www.mercstuff.com/gimbalbearing1.htm

 

[bheston]

Re: New boat has bad vibration when running

I found a slide hammer at the farm that had a 1/2" bolt thread on the end, and welded a nut to some flat steel to make a "hook" that would slip through the bearing and hook around the back side of the bearing. After a couple dozen good smacks the bearing was out. Thanks again for the help