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[david48]

I am on with fitting the prop shafts on my Fairmount build and it crossed my mind about wear on the ends of the tubes. Method of fitting props is Loctite nut lock and a lock nut snugged up to the prop and a 4mm brass washer then the shaft slid into the tube, inboard end is washer and lock collar .The more experienced builders of you please can you tell me if the end of the tube wears much , I know it a piece of string answer ,it will never wear if not used and it will wear out if run 24/7/365. Do you give the shaft any end float ,when I started this build I did not know about bearing tubes /shafts,and it was to late to change,as it is there is slight lift in the shaft I see this  as good as it gives a grease space .Has any one machined their shafts with a spiral grove,not very deep so that it spins the grease round the shaft . I am thinking the outboard bush will be water lubed as in a real cutlas bearing on a yacht .
Thanks for help ,
David

[Peter Fitness]

David, I, and a lot of other modellers, use a suitable size O ring between the washer and end bearing, at both the inboard and outboard ends of the tube, When the nut is nipped up - not too tight or it will bind the prop shaft - it seals the prop tube very well. The attached photo of a prop tube assembly I made, and which I have posted on the forum before, shows what I mean. I hope this helps.


Peter.

[CGAux26]

You need a little end float, maybe .005" to make sure the shaft can turn freely.  Just enough to feel it move. 


As to wear of the shaft tube, I put a nylon washer at each end of the tube, then the lock collar on the inboard end and the locknut and prop on the outboard end.  The nylon washers absorb any wear, which has been minimal in my oldest boat, now 7 years old.  Put the nylon washer, locknut, and prop on first, then set the end float by adjusting where the lock collar goes.


No need to thread the shaft.  Just grease it before inserting it into the tube.

[CGAux26]

I would not use a brass or steel washer where i put the nylon washers.  You want the washers to wear, not the shaft tube, so make the washers be a softer material, like nylon or the O-rings someone suggested.

[david48]

Thank you gentlemen for you replies, I'm not sure about the nylon washer the reason being ,when I was fitting, nylon pipe chaffing against metal pipe work always wore the metal away this was common on fuel systems. I understand that a sacrificial washer material will be better than wearing the prop tube end . I have been looking at a 4mm thruster bearing but the OD is a lot too big it just will not look right . I will try a combination of washers  and "O" ring . This might sound over the top ,I am waiting for the grease to come its the grease thy use in feathering props on yachts ,I've used it on the real thing it is very light and will not wash out ,we use it when we service the boat so my mate is sending it .
Thanks again
David

[Peter Fitness]

I have to say I've never had a problem with wear at the end of the shaft tube. I use either brass or stainless steel washers, and even after 10 years of regular use there is no obvious sign of wear. It would probably be an issue in fast or powerful boats, but as mine are neither I don't need to worry.


Peter.

[derekwarner]

Purely from a mechanical point, one would consider a stainless steel washer rotating against a stationary brass bush or tube end, with water as the lubricity be superior to a nylon washer in the same application

It is acknowledged that pure Nylon does not absorb or swell in water .....however there are so many generic names for thermoplastics...& they all look the same in a billet of bar stock, but alas some absorb and swell with water or and an increase in heat   which can occur in out of water bench testing

We also consider that with a prop shaft tube, there will be a minute migration of lubricant from the grease packing

I still have a 1/2 a jar of Dow Corning rubber grease  ......which was the forerunner of todays commercial waterproof bearing grease .....

With respect to longitudinal clearance, yes by all means and say 0.003 to 0.005" in this type of application is fine....remembering it is essentially negated by directional rotation thrust  .....

Yes in both directions, the actual prop shaft is in tension created by that same directional rotational torque/thrust .......

However in real marine applications, an inboard propeller shaft thrust bearing assembly can be the size of a 200 litre drum or a very large tea chest........ ...Derek




. Derek

[david48]

Maybe over thinking it a bit on my part , as you say if you have not experienced wear Iwill use the "O" ring system . It is just me some folk will just lube the tube fit washers and collar and go for it .but it all seems a bit crude to me .
 Thank you all for the input ,and will make that do for this thread .
David