PTFE fork bushes

I was keen to make up some fork bushes myself, got the lathe, need to justify it's existence at home. Sooooo I could not get Turcite in Australia, so my search of engineering plastic's indicate virgin PTFE offers the lowest coefficient of friction, is considered pretty strong compared to Acetal products such as Turcite etc. Very expensive, I was quoted over $200 by one mob, but after scouting around I got an offcut for next to nothing. I am in the middle of installing my newly arrived Landsdowne dampers. I have already made and had running some bronze extended top bushes, that run really freely, better than the original bronze bushes.

I am seriously wondering how much of an improvement the plastic bushes will give over free running bronze and original steel sleeve bushes? And should I keep the extended bushes or shorten them up, now that the new dampers should look after top out's.

So you guys with the plastic fork bushes, are they a noticeable improvement? And LAB would you use the long bushes or just use standard lenght?

Cheers Richard

stockie2 said:

And LAB would you use the long bushes or just use standard lenght?

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John (Lansdowne Engineering) is the person you really need to be dealing with as he already has some experience of making plastic fork bushes for Roadholders. The extended upper bushes are supposed to allow the hydraulic rebound bump stop to work as it appears it was intended to, and I fitted the RGM extended bronze upper bushes to my Commando's forks but they didn't appear to make any noticeable difference that I could detect.

just my 2 cents worth, feel free to ignore my comments.
Teflon has good wearing capabilities, but it is very soft which may cause some problems in this application
another concern is any minute particles of foreign matter that gets caught between the teflon bush and stanchion is likely to get imbedded in the teflon and cause scoring or wear on the stanchion.
I guess if teflon fork bushes were the go then there would be plenty of replacement teflon bushes on the market,
they would not be expensive to mass produce as they would be molded in a similar way the standard sintered bronze
ones are made.
I think some OEM bushes have a coating ,possible teflon but its probably no more than 1 or 2 thou thick.

every modern bike has teflon bushes, have a look for Glacier bushes, these are a thin layer of teflon over a bronze substrate on a thin wall steel bush, great product, very durable, they even use them for crankshaft main bushes these days, the problem is they are available in stock sizes not applicable to the oddball OD of the norton fork staunchions.

its easy to have them made to your desired size but it would require a large volume ordered, I had the sintered bronze bushings made for the TLS front brake camshafts , if I remember the same company made the teflon coated bushes mentioned, very economical in large volume. Hmmmmmm

Stockie , top bush , You require to watch the clearance, If the stanchion is a good fit when warm, it can grab the bush when cold,
I turned a set up on a warm afternoon, [nice sliding fit]in the morning after a frost they where solid, the stanchion had shrunk onto the "yeilding bush" After a few hours in the house they where loose again!

Teflon coated [50 microns] on steel as per modern stuff is more temperture resistant,that solid plastic,
PTFE as a poor Modulas and will creep under load, I have made a few from Graphite Nylon, which is stronger.....PTFE PEEK is supposed to be good, But costly.
My general view is time spent getting the stanchions true in all plains is 90% .
Add 20% Slick 50 to the 5 grade fork oil...works wonders!

PTFE is a bit soft. I've decided on Turcite and they work great. Very slippery and that makes for a nice smooth ride. You have to slit the plastic to avoid diameter changes with temperature variation.

The aluminum sleeves provide a quiet hydraulic top out and also need slits so they are a hand press fit and stay in place. I provide a brass ball to plug the lowest 1/8" bleed hole in the fork tubes and that makes the alum sleeves actually work. The bottom alum sleeves fit on the bottom of the damper tubes and provide a hydraulic bump stop. With these bits the forks work as they should with no more clanking or stiction. The aftermarket dampner kits don't need the alum sleeves.

More power to those who make them on their own. You can get some hints from the photos below. Those who just want to install pre-made slippery plastic bushings that have been "developed" can get them at jsmotorsport.com. I'm on my 2nd batch so far. The very first ones were created for my monoshock 850 road racer in the 1980s.

Slits are visible in the bottom photos.

stockie2 said:

... virgin PTFE offers the lowest coefficient of friction, is considered pretty strong compared to Acetal products such as Turcite etc.

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Sorry, but that needs a small correction: Turcite is a brand name - by TSS Trelleborg Sealing Solutions - and not a material spec. It actually comprises a bunch of slightly different materials, most of the with a PTFE matrix, some with a ECFTE. The properties of all Turcite materials are generally better than "acetal" aka POM. Most turcite variants are bronze filled for both strength and stiffness and the way to go is actually to etch shortly them after machining. This removes the bronze bits in the surface and thus only the PTFE is the wear partner but the part itself retains most of its strength. In a perfect world they would run in a hard anodized and honed bore.


Tim

Thanks to all for answering, I am keen to get the new dampers in, and after your comments and reading up on machining PTFE plus the general consensus that it is probably to soft, I think I will add some friction modifier to the fork oil for now, this time around. The Glacier bush sounds cool if it could be sourced with the right ID etc. I was disapointed to notice a small blemish on my original stanchions, a small bubble of chrome has delaminated from the parent metal. I guess in time it will break off. But for now I will keep an eye on it. I am pretty wired in to stripping the forks now, less than 30 minutes once on the hoist and I have it all apart. So no big deal to review in the future some time.
Cheers Richard

Forgot to point out the hazards of turning PTFE, micro dust if inhaled is well nasty. Use a mask .
Or under coolant.

Thanks John,
I used coolant to size up a piece last night, but for now we wil put my prize piece of ptfe in the rod rack, and I will just fit up your dampers and ride tomorrow, beautiful sunny weather here this week end. I will get some friction mod, like you said. Do you think it is worth leaving in the longer top bushes and plugging the small holes in the stanchions?

I notice you quote 5wt oil and your instructions included said 10wt. I have 10wt and some very nice 7.5wt motul factory line. I guess your update to lighter oil is winter experience, do you think in milder climes the thicker grades would be a better starting point?

Cheers Richard

stockie2 said:

Thanks John,
I used coolant to size up a piece last night, but for now we wil put my prize piece of ptfe in the rod rack, and I will just fit up your dampers and ride tomorrow, beautiful sunny weather here this week end. I will get some friction mod, like you said. Do you think it is worth leaving in the longer top bushes and plugging the small holes in the stanchions?

I notice you quote 5wt oil and your instructions included said 10wt. I have 10wt and some very nice 7.5wt motul factory line. I guess your update to lighter oil is winter experience, do you think in milder climes the thicker grades would be a better starting point?

Cheers Richard

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Richard ,
the dampers are designed to work in the standard fork set up, No longer bushes required, the stanchion holes will have no effect so leave them.
Oil 160cc 10 grade with 20% slick 50 will be right for your clime's. Thats 160cc total!