Delrin rudder bearing and marine grease

[Eigenvector]

I've use a lot of Delrin 500 AF subsea. It impregnated with Teflon and therefore self lubricating.

[Segelplaner]

WD-40 seems to be a dry lubricant, but I guess that will not work?

[Chotu]

No grease! Delrin should not be greased.

I have delrin rudder bearings like these. They should not be greased.

[a64pilot]

Moly as in Molybdenum disulphide is actually abrasive, it’s an excellent high pressure lube, but abrasive. It’s probably most common use is in CV joints.
I know it’s abrasive because I used it in powder form to lubricate the ammo flex chute in something I used to support, normally we used CLP, but it’s a liquid and in desert environments it attracted so much sand it quickly became like valve grinding compound, so I used powered moly be damn as we called it, it caused wear, but worked .

I think it would eat up something as soft as Delrin.

Maybe a soap based grease? Or a silicone grease?
https://en.m.wikipedia.org/wiki/Grease_(lubricant)

[a64pilot]

Originally Posted by Segelplaner

WD-40 seems to be a dry lubricant, but I guess that will not work?

WD-40 isn’t very good at all, best use is for household or something.
It seems to actually evaporate and is short lived at best.

[kmacdonald]

Originally Posted by thinwater

No grease, no way. It won't reduce friction measurably. There is no risk of corrosion or galling. It won't reduce wear. In other words, ther eis no upside. But...


Grease will attracting and hold grit. This FAR outweighs any benefit.


Also observe that lubing plastic bearings on deck hardware is never recommended. You can ask them why.


Don't do it.

I'd trust what Thinwater says. He only comments if he knows for sure.

[mtarcher]

We have a delrin bearing for our rudder (the assembly made by Tides Marine). By year 9, the helm became very difficult to move and I pulled the rudder to fix the problem. Tides advised to only gently sand the post, but not the bearing, as any abrasive action on the bearing would "swell" the surface.
I'm sure greasing the bearing would provide an adequate lubricant. Like many of the previous members stated, I wonder if the grease might create a future problem by attracting grit or sand. If it did, I suspect the bearing may be damaged over time.

[GordMay]

Several contributors have indicated that the reason for not greasing the bearing is because the grease attracts dirt/grit.

Maybe another way to think about the dirt/ grit, is to say that the grease does not attract dirt/grit, but what grit that does come in contact with the grease has a better chance of sticking .

[thinwater]

Originally Posted by GordMay

Several contributors have indicated that the reason for not greasing the bearing is because the grease attracts dirt/grit.

Maybe another way to think about the dirt/ grit, is to say that the grease does not attract dirt/grit, but what grit that does come in contact with the grease has a better chance of sticking .

Correct. And maybe we have all been missing the point... a little.


Where does the grit come from? This is the real question. Seawater is quite clean.



In my experience--and I am SURE this is regional--the grit that wears rudder bearings is either lime from seawater drying, or marine life. You don't get much growth in tight spaces, in the absence of O2, but you get some, perhaps enough to create abrasives.


So how do you eliminate the abrasives? When replacing bearings I always wipe the shaft down with weak acid to get rid of the lime build up, but it will return (the upper bearing was above the WL). Keeping it below the waterline would probably fix that. Marine growth could be discouraged by a few zinc ions.


Put on your thinking caps. If you can eliminate the grit, the wear will go away. Grease will help when there is grit, but it will also prevent the grit from flushing out.


Is a puzzler.

[a64pilot]

You answered where the grit comes from. We don’t sail in a desert of course, I have a K&N air filter on the engine primarily for just dust, which we still have.

However I’m of the belief that any grit and or old hardened grease can be flushed out if there is a means of pumping in fresh grease, so the grit issue isn’t an issue.
It’s how grit is dealt with in bulldozers, farm equipment and other machinery that is truly grit contaminated grease, flush it out regularly.
I’m thinking a soap based thin grease may be the ticket, it’s also very widely available, usually chassis grease is lithium, which I think is soap based.

So bronze is I guess, sort of self lubricating? If I let my boat sit for a couple of weeks or more the rudder is stiff, but frees up very quickly, and as far as I know my bearings can’t be lubricated, and are quite old.

[jimbunyard]

Delrin absorbs water. You 'll probably need a looser fit if you don't want it to get tighter over time. It doesn't need grease. Perhaps a better choice would be UHMW or HDPE or Vesconite, which is a plastic specifically designed for immersed shafts.

[Jim Cate]

Originally Posted by jimbunyard

Delrin absorbs water. You 'll probably need a looser fit if you don't want it to get tighter over time. It doesn't need grease. Perhaps a better choice would be UHMW or HDPE or Vesconite, which is a plastic specifically designed for immersed shafts.

Yep, this is true! On our previous boat the lower rudder bearing was a Delrin sleeve inside an aluminium tube. Over the years the Delrin absorbed water and this caused it to swell slightly. Since the sleeve could not expand outward, being contained in the tube, it expanded INWARD, reducing the clearance on the shaft, and it began to bind up. Palmer Johnson, the builders of the boat advised dropping the rudder and reaming the bearing to nominal size. Big PITA, but it did the job... around every five years.

There are better materials than Delrin for submerged bearings, as Jim notes above, but they are more expensive than Delrin and hence not used by OEMs very often... they don't have to do the crappy job of maintaining the boat!

Jim

[GordMay]

Originally Posted by jimbunyard

Delrin absorbs water. You 'll probably need a looser fit if you don't want it to get tighter over time. It doesn't need grease. Perhaps a better choice would be UHMW or HDPE or Vesconite, which is a plastic specifically designed for immersed shafts.

Water absorption (saturated) = Nylon 9% / POM acetal 0.8% / Vesconite 0.5% / UHMW 0%.