Installing delrin rudder bushings in rudder tube

[drumbeater]

Now that we are moving along with the repair of the rudder shaft, I will soon be reinstalling the rudder.

My understanding is that the bushing should stay fixed inside the rudder tube and the shaft will be greased and will rotate inside of the bushings.

What would be an acceptable way to secure the bushings to keep them from rotating? Epoxy would be too permanent. 3M 5200 would also be too much I think. Maybe 3M 4200? Any other options? I think there has been some wear in my rudder tube which may allow the bushings to rotate.

 

[Witzend]

Epoxy will not stick to Delrin very well. Delrin is smooth which is why is works well for a bearing. Epoxy is a mechanical bond requiring surface roughness to create the bond.
Dose the bearing have a flange? Anyway to use SS screws through the flange?

 

[Chris Patterson]

Making anything stick to delrin may be a bear. While I generally stay out of the sealant/epoxy debates, maybe drilling some very shallow dimples on the outside radius of the bushing may help give it some bite..

 

[drumbeater]

One of the bushings is below the waterline so a screw is probably not a good idea. The one up top could benefit from that.

The bushing is not perfectly round on the outside. It has flat spots at 12,3,6, and 9 oclock positions. If I could fill those gaps with something stiff it may hold in in place. Just having a hard time imagining what to use in those gaps.

Looks like this:

 

[kloudie1]

I have seen these done with thickened epoxy paste. The trick is to grease the rudder shaft so the epoxy doesn't stick to it . rough up the outside of the bearing a little, . clean the pockets in the boat tube, put in the paste then the bearing then put the rudder in so that the bearings are correctly aligned.. after the epoxy sets, the bearing will not turn because of the flats.. When it is time to change, ya pull the rudder cut the bearing, grab one edge with locking pliers, and pull the bearing out.. Chances are the bearing will last a LONG time..

 

[RichH]

To prolong the life of delrin rudder shaft bearings .... POLISH the rudder shaft where the bearing 'rides' to a bright 'mirror like' shine.

Delrin doesnt like 'abrading surfaces' and quickly 'transfers' to rough surfaces, thus the rapid wear. DONT use 'lubricants' on delrin ... will soften it and make the 'abrasion-transfer' wear worse.

Many boat classes have 'cobbled' much better substitute bearings out of "carbon powder filled + high density/chopped fiber Filled epoxy, sometimes with chopped up teflon dental floss as the 'lubricant' mixed and layered onto the bearing ID for good measure. WebSearch: Pearson-26 + rudder + bearings

 

[Don12364]

On my previous boat (not Hunter) I used PTFE because the previous nylon bushings fitted by the builder swelled up and the rudder seized solid!
Beware Delrin because it has 0.2% expansion when immersed in water and a little less when in 100% RH. See page 15 in http://www2.dupont.com/Plastics/en_US/assets/downloads/design/DELDGe.pdf.

Most bushes are made a fairly tight push fit so mostly they don't move in their housings.
Make them a little slack on the rudder shaft to cope with the shrinkage when pressed into their housings and also allow for the expansion inwards due to moisture. The material goes inwards because it can't expand outwards due to the housing.

 

[RichH]

Absolutely correct by Donalex about 'swelling' due to water uptake.

Also the approximate precise clearance (measured AFTER press-fit into a housing) is approx. 0.003"+ clearance for each 'inch' of shaft diameter ... a 1.5"Ø shaft would require a minimum of ~0.005 inch 'clearance'.

And again, the surface finish on the shaft is VERY important - 'mirror like' if can.