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Old 12-05-2012
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Should I change shaft size

I have a Sabre 28 originally powered with an Atomic 4. It now has a Universal M3-20. I am replacing coupling, shaft, stuffing box, cutlass bearing and prop. The original shaft was 7/8". I could now move up to 1" which I think non-A4 28s used. Any thoughts on this or is it such a small change it doesn't really matter. If there are any pro's I will go with the 1".

Looks like:
-Small increase in cost
-7/8" appears to be plenty strong and would be a little lighter
-1" is a little more common but does that really matter

Going with:
-Aqualoy 22 Shaft from Deep Blue
-Duramax Cutlass bearing
-Duramax Ultra X Packing
-Campbell Sailer Prop

-Joe
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Old 12-05-2012
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Re: Should I change shaft size

The outside diameter (OD) of the Cutless bearing and inner diameter (ID) of your stern tube used with your 7/8" shaft may be the limiting factor.
Looking at the various Cutless bearing options here: Cutlass Bearings - Johnson Duramax Cutless Bearing - Naval Brass Inch
it seems you should be able to go to a 1" shaft without having to re-bore the stern tube.

The other thing that jumps out at me is all the 7/8" cutless bearings are 3-1/2" long while all the 1" bearings are 4" long.

If you DO change shaft sizes you will likely need a new shaft coupling to accommodate a 1" shaft. You will also need a new stuffing box for the 1" shaft.

If it was me I'd keep the 7/8" shaft size but I am cheap and lazy.
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Re: Should I change shaft size

Thanks for your comments. I hadn't looked at the 1" cutlass bearing length, it would be 1/2 too long so I would have to cut that. Hadn't thought about the shaft tube either. I am sure it would clear but it was a little closer on one side so the clearance would be even further reduced with 1". 7/8" looking better all the time.
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Old 12-05-2012
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only if she prefers length over width
-JD
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Old 12-05-2012
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Re: Should I change shaft size

Since the original shaft was bronze, a new shaft of stainless will be inherently stronger. So you're ahead of the game from the start. I see far more hassle going with a larger shaft and can't think of a reason to make the change.

Sabre properly sized the shaft when designing the boat. When I did the same job on our Sabre 28, I used bronze. But it's virtually impossible to obtain bronze these days so I used SS when I did the job on our 38.

I don't see a coupling in your parts list. It is mandatory when changing the shaft. Do not try to reuse the old one if you stay with 7/8"
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Re: Should I change shaft size

I'd probably stay with 7/8" if I could find the right prop. If I could only find the right prop for 1",well you know what I'd do. I'm a cheap bastard so a used prop would be the limiting factor for me.
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Old 12-06-2012
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Re: Should I change shaft size

Quote:
Originally Posted by sww914 View Post
I'd probably stay with 7/8" if I could find the right prop. If I could only find the right prop for 1",well you know what I'd do. I'm a cheap bastard so a used prop would be the limiting factor for me.
Can't you get a bushing to bring the 1" down to 7/8"?
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