View Full Version : Vibration

04-11-2004, 07:31 PM
I hit something on the river last weekend. I bent my prop, took it off, got it fixed, put it back on, and still I have the vibration. Could it be the shaft? If so, how do I check and see if it is when dry? And how do I get it off and install new one?

04-12-2004, 12:01 PM
Sorry to hear about your troubles. Tell us what you hit? How fast? How much prop damage? Was the rudder involved? SS or nibral prop?

If it was just a low speed prop "ding" while you moving in shallow water, the prop may be out of balance even though it has been "fixed". If it was a high speed against something solid like a log then consider a shaft or alignment issue. Check the rudder also.

Until recently I would have said to drop the shaft out anyway. Rolling the shaft on a machined flat surfaface is a quick and dirty way to check for bends. Brian Raymond recently suggested that the shaft coupling flange was machined after installation on the shaft. He therefore advises to remove the shaft through the engine compartmet (engine lifted). Separating the shaft from the flange and dropping the shaft back through the log (as I have always done in the past) would negate the care taken on initial assembly. So now checking the shaft becomes an engine out job. Not a big deal but maybe more work that you had hoped for.

So what would I do? If it was a big hit, take it in and have it professionally checked. You should not run with any vibration in these boats. If it was a small "ding" Check your alignment at the flange (see previous thread). Then check by swapping for a prop you know is good. Be careful that the key is not keeping the prop from seating properly.

Stainless props are very hard on the drivetrain with any sort of a prop strike. They are are also not repairable if the damage is significant at all. The nibral props will absorb alot more shock and can be brought back to spec by a good prop man.

I am sure I don't have to mention this but NEVER hit the prop to get it off or on. ALWAYS use a puller. Sorry to mention something so basic but I have seen alot of needless damage over the years. That also means that if you carry a spare you need a puller with you. They are not expensive. I made one up from a carpenters C clamp. I have seen guys spend $$$$ on an inboard boat and then buy every option available to make it look good but no spare prop or puller.

04-12-2004, 01:38 PM
Another way to check the shaft would be to hookup water start it up and put it in gear. I use something like a fake-a-lake to get water to the water intake. If the shaft is bent you should see it unless it is a very minor bend.
Just a thought it would be easier than lifting the motor.

04-12-2004, 02:05 PM
Good idea Bruce. I have often thought that if you could set up a jig with a fixed arm it would make it easier to see any shaft deflection. The bend would have to be major to just eyeball it. Make sure the cutlass bearing is in good shape. Also make sure the cutlass bearing has water on it if you are turning the shaft out of the water.

04-12-2004, 09:16 PM
Maybe do as Bruce suggests, plus set-up a dial-type run-out gauge. Could anchor it to the strut.

Just to reemphasize, it doesn't take much prop damage to cause vibration.

About the extent of repair possible without proper tools would be dressing the edges slightly with a file to smooth a nick.

I bought a spare and carry it on-board in a foam-lined case, along with a 1 1/16 wrench, puller and spare nyloc nuts and keys. You can by such kits or make em up.

04-12-2004, 11:23 PM
Well, I hit it at idle speed in a no-wake zone....Its a 4 blade Nibral. When I look under the boat, where the shaft goes into the hull it looks off. Gap is bigger on 1 side than the other...

04-12-2004, 11:25 PM
Oh...dont know what I hit....Prob. a log.

04-13-2004, 01:56 PM
The plot thickens.
Two possibilities here:

1) The shaft was aligned a little off the centre when is was set up (but still correctly aligned). No worries there.

2) The impact moved the strut or bent the shaft.

If it is the latter they may be visible stress # in the gelcoat around the strut mount. Look there for damage. If there is no damage then try rotating the shaft by hand (boat in neutral, motor off! cutlass bearing wet. There should be no binding. The shouldn't be a point during the 360 degree rotation that the shaft seems to hang up. You are into professional repairs if there has been any movement of the strut.

Have you had a chance to try a good prop and to check the prop is seated on the taper or alignment at the flange yet?

04-15-2004, 08:49 AM
Here are some pictures

04-15-2004, 08:53 AM
Here is the shaft...

04-16-2004, 07:49 PM
I didn't get the shaft ( for once ).