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Old 06-05-2016, 07:03   #1
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Prop Shaft/Cutlass Bearing Clearance Tolerances

I think I'm going to have to replace my prop shaft which measures 35mm. However, it's very difficult to find metric sizes where I am and costly to turn down an entire shaft. One supplier has offered an inch-and-three-eighths shaft, which is .003" less than 35mm. Do any engineers out there know what the acceptable clearances are? Thanks.

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Old 06-05-2016, 07:34   #2
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Re: Prop Shaft/Cutlass Bearing Clearance Tolerances

.003 seems more than acceptable since that works out to one and a half thou. per side ( about the thickness of a piece of paper).
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Old 06-05-2016, 08:00   #3
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Re: Prop Shaft/Cutlass Bearing Clearance Tolerances

Depends on how worn your bearing is too. Slide the new shaft in, lock it on the engine then grab the other end and check how much free play there is.

I say this as I know that cutlass job is due every couple of years and so the timing seems perfect when your shaft is out.

The small difference you mention is indeed small.

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Old 06-05-2016, 08:18   #4
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Re: Prop Shaft/Cutlass Bearing Clearance Tolerances

Quote:
Originally Posted by perchance View Post
.003 seems more than acceptable since that works out to one and a half thou. per side ( about the thickness of a piece of paper).
Thanks for the post. However, someone else just pointed out that my existing coupling would now be .003" too big and I'm not comfortable with that nor do I want to replace the coupling.
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Old 06-05-2016, 08:23   #5
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Re: Prop Shaft/Cutlass Bearing Clearance Tolerances

Can be made up for with seals and bearings....

It should be plenty strong for the task.
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Old 06-05-2016, 09:08   #6
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Re: Prop Shaft/Cutlass Bearing Clearance Tolerances

The cutlass bearing wouldn't be a concern in my opinion.

The coupling might be, I'm not sure. But also keyway should be considered, which would be .250 inch I think. What is the keyway size in your metric coupling?
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Old 06-05-2016, 09:14   #7
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Re: Prop Shaft/Cutlass Bearing Clearance Tolerances

Following shaft tolerance information per Aqualoy and Aquamet shaft catalogs:

-Shaft diameter tolerance from nominal diameter for shafts between 1 & 1.5" diameter:
Minus .001" to Plus .002"

-Shaft to bearing tolerance for shafts between 3/4" & 1.3/8": +.003 to +.008"

Similar tolerances probably exist for metric size shafts. Seemingly then a well supplied distributor of shafts could select inventory such that the difference between your shaft and a new 1.375" shaft could be nil. But to arrive here you need to know an accurate dimension of your existing shaft.

DougR
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