Author Topic: Prop shaft center bearing  (Read 109 times)

SV Alfresco

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Prop shaft center bearing
« on: December 04, 2019, 07:20:37 PM »
I have a problem with vibration in the drivetrain on my 367. I noticed that the prop shaft is touching the top of the shaft log. Looks like the v-drive needs to be lowered and aligned. We checked the prop shaft and it runs true. The mechanic I'm working with wants to add a bearing in the shaft log because the length of the shaft between supports exceeds some standard and possible whipping of the prop shaft could be causing some vibrations. I  think we have uncovered more than enough possible problems that could be causing the problem (i.e. v-drive alignment and cutlass bearing). I am resisting the center bearing idea because I have not seen this on this forum. Any suggestions or opinions would be appreciated.

Thanks,
Mike
« Last Edit: December 05, 2019, 02:55:04 AM by SV Alfresco »

Jim S

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Re: Prop shaft center bearing
« Reply #1 on: December 05, 2019, 07:59:43 PM »
An improperly aligned shaft coupling to the v-drive will cause the vibration.  The v-drive to shaft alignment is critical to prevent premature wearing of the seals of the v-drive.  Most boats have the transmission/shaft coupling to align, our boats have the v-drive.

Where would he put a pillow bearing that would not interfere with teh shaft gland?
Jim S

SV Alfresco

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Re: Prop shaft center bearing
« Reply #2 on: December 06, 2019, 10:08:39 AM »
He wants to glue in a plastic housing and a cutlass bearing into the shaft log and then convert the water tap on the PSS shaft seal to pressurized with a hose off the engine raw water to get water to the bearing. He gave me a chart that shows the max distance between supports for a 1-1/8 diameter shaft is 4'9". I think that there is more than just shaft diameter involved in possible shaft whipping. Maybe this is necessary on bigger, more powerful boats but I haven't heard of this before.

Mike
« Last Edit: December 06, 2019, 10:37:09 AM by SV Alfresco »

Jim S

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Re: Prop shaft center bearing
« Reply #3 on: December 06, 2019, 08:25:33 PM »
Do you still have he original bronze shaft?  It may test true, but they are more flexible than a replacement Aquamet shaft.  Did you repower with a larger engine that would put more torque on the shaft?

Incidentally, I have never seen a 365/367 that needed a pillow bearing.  I suspect something else may be going on and the bearing may cure the symptom, but not the cause.
Jim S

SV Alfresco

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Re: Prop shaft center bearing
« Reply #4 on: December 07, 2019, 09:31:48 AM »
The shaft is stainless. The engine is a 39hp Yanmar. The trans is a ZF. The final ratio is 2:1. The prop is the original 17" 2 blade, which I might replace.  I suspect once the v-drive is reconditioned by Walter and everything is aligned properly, everything will be fine. I think you confirmed what I thought, that the pillow bearing is not necessary.

Thanks,
Mike