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Wear - Shaft

Posted: Sun Apr 22, 2018 11:33 am
by Leviathon
So replacing cutlass bearings, what is normal for wear on the prop shaft where it rides on the bearing? Is there a tolerance rating? Trying not to break out another thou.

Re: Wear - Shaft

Posted: Sun Apr 22, 2018 12:11 pm
by Busia
Normal would be zero wear. You have a stainless shaft in a rubber bushing, lubricated with water. Normally the rubber cutless will wear and be replaced. How much wear is allowed is affected by how big is the shaft, how well it is aligned, how much vibration you have, how much torque you are putting on it, cost to change it, how critical is it. I would at least make sure the shaft is smooth with no nicks or sharp edges. A real machine shop can make new shafts easily, they are not complicated.

Re: Wear - Shaft

Posted: Sun Apr 22, 2018 12:42 pm
by jralbert
Advice from a boat maintenance article I read: double the wear you measure on one side of the shaft. If, for example, there's a 1/8" notch, it's actually 1/4" because the wear, of course, is on both sides of the shaft. This example is extreme - 1/4" is a failure waiting to happen. Hope yours is just an insignificant scratch at worst.

Best, as Busia points out above, is no wear.

Google turns up many discussions on shaft wear, some seem to be more informed than others.

Re: Wear - Shaft

Posted: Sun Apr 22, 2018 1:38 pm
by Leviathon
Unfortunately I think most of these 45+ year old boats have not been routinely maintained, so 45 years worth of use, probably better replace it. Will just have the shop that is making the struts and rudders throw a couple shafts on the bill.

Re: Wear - Shaft

Posted: Sun Apr 22, 2018 3:58 pm
by TinLizzy
They can use the old shafts for the rudders if they are 1".

Re: Wear - Shaft

Posted: Mon Apr 23, 2018 9:06 am
by EWRice
You are going to have some wear and that is normal. A normal wear is a very shinny area with smooth transition into the shaft area outside the bearing. You may feel some smooth grooves in the shaft, but as long as you can't hook your fingernail in them you are generally ok. The most accurate and unscientific way to check is to slide a new cutless bearing on. If there is little to no play you are good to go.

I second using the old shafts for a new rudder shaft.

Re: Wear - Shaft

Posted: Mon Apr 23, 2018 4:34 pm
by Leviathon
Now that the rudders are done - Yes - that is an obvious and excellent suggestion. That did not cross my mind!! Bottom line is, I was going to have to have some work done to the shafts as the crusaders with reduction gear add about 6 inches to the drive train. I would have had to cut them down anyway. Will see as soon as I get engines in how long of a prop shaft is required and just have them cut to size. Thanks All!