Shaft wobble

[Red Hatt]

I have a shaft wobble at the back of the transmission . 8 v 71 ti The engine is properly aligned . There is know excess where in the cutlass bearings . There is know vibration standing over the props when running. If the prop is causing the the wobble I thought about getting a diver to remove the prop and then run the engine in gear and check for wobble. If there is know wobble then it must be the shaft. If anybody has any other suggestion that would be great. Thanks

 

[saltshaker]

Are you sure everything is properly aligned? Is the shaft going through the center of the shaft log and the struts? Are your engine mounts in good shape? Check to see if there is play in the output flange form the gear.

 

[Glory]

If the the shaft was out recently maybe the key is set correctly on the engine end.

 

[Andy B]

Check engine alignment again , rotate the shaft 45deg and check, then rotate another 45 deg and check and another untill you have made a full rotation. if it changes shaft is bent or couplings are untrue .while the shaft is uncoupled make sure the trans output flange is nice and tight.

 

[Red Hatt]

Check engine alignment again , rotate the shaft 45deg and check, then rotate another 45 deg and check and another untill you have made a full rotation. if it changes shaft is bent or couplings are untrue .while the shaft is uncoupled make sure the trans output flange is nice and tight.

Thanks for all the replies. I'm having the alignment rechecked at the end of next week. If that's not it I'm going to have the boat hauled for bottom paint . I will pull the
Shaft out and send it out to see if it's bent. I haven't hit anything so I doubt that's the problem.

 

[dsharp]

If the shaft is oscillating more than likely you have an alignment issue. The vibration is usually a bent blade. If you're due a bottom job I'd wait until then to remove the props and have them reconditioned. Make sure the prop doesn't ride up on the key.

 

[Red Hatt]

Had the alignment done by two different people and it checked perfect. what do I check for next shaft ? then strut ?

 

[mike]

If you have an Alison M20 series transmission, double check the transmission output shaft flange coupling to make certain the trans shaft to flange connection is tight and solid. They have a history of coming loose.

 

[rsmith]

How bad is the "wobble" ? At what RPM? Any shaft will take a set if it sits for a long time unused or turned. Heavy machinery and big ships have many times a Sunday drive system to slowly turn the shafts to keep them. From taking a set and ending up bowed. If it's not vibrating at speed I wouldn't worry. It might true it's sely back up again after some running

 

[Red Hatt]

The boat had been sitting for six months.

 

[SEVEN]

Sounds like that is the possible issue.

 

[q240z]

It's unclear to me how you can simultaneously have shaft wobble that's visible from inside the boat and good engine/shaft alignment for a full 360° rotation.

I had very good results with a cheap-o Harbor Freight 1" travel machinist's dial indicator when I did my shaft/engine alignment on my Roamer project. For a $17 investment, you should be able to check your gear coupler and shaft to figure out exactly what's wobbling.

 

[Andy B]

Are you sure the engine is running smooth? And the vibration is not coming from the engine?

 

[rsmith]

Are you sure the engine is running smooth? And the vibration is not coming from the engine?

He said no vibration but a wobble at the engine coupling. I hope everyone here knows engine alignment must be done in the water with the boat loaded as it would be run. All boats flex and move. In alignment today with a cold engine might be not the same when she's a hot mess after a hard run and pounding

 

[q240z]

So, a wobble at the coupler after sitting six months might work itself out after a hot run, normally loaded?

I think I'd like to see no wobble period.

 

[Andy B]

He said no vibration but a wobble at the engine coupling. I hope everyone here knows engine alignment must be done in the water with the boat loaded as it would be run. All boats flex and move. In alignment today with a cold engine might be not the same when she's a hot mess after a hard run and pounding

I have seen a engine with a bad main bearing show up as a wobble at slower speeds then get a lot worse as engine speed increases. At this point sounds like worn cutlass bearings.

 

[rsmith]

So, a wobble at the coupler after sitting six months might work itself out after a hot run, normally loaded?

I think I'd like to see no wobble period.

And you did your alignment on the hard???

 

[saltshaker]

I've always been told alignment in the water. When I had my shafts replaced they did the alignment on the hard and then again once I was back in the water. Boats are designed to be supported evenly by the water. Very different from being on the hard and only supported by a few areas of the hull. try opening and closing some doors while on the hard and you'll find some that don't line up as the do when in the water.

 

[Boatsb]

I've always been told alignment in the water. When I had my shafts replaced they did the alignment on the hard and then again once I was back in the water. Boats are designed to be supported evenly by the water. Very different from being on the hard and only supported by a few areas of the hull. try opening and closing some doors while on the hard and you'll find some that don't line up as the do when in the water.

Rough it in on the hard but still finish the job after she's had a couple of days to settle.

 

[34Hatt]

Rough it in on the hard but still finish the job after she's had a couple of days to settle.

I do that except I make it best as I can on the hard then again in the water and Never seen a difference in my Hatt.

Other boats all the time but the hatt I have done it 3 times now never seen a difference