New fork bushing stiction

BrianK · Mar 29, 2010

Woulda made sense to ask before doing, but hey....

Just rebuilt the forks, including putting in new top bushings. One was a nice sliding fit, the other a bit tight - movable by hand but with significant drag.

I went ahead and installed on the theory that the stanchion will fairly quickly wear down the "excess" bushing and then I'll have a good fit.

Mistake?

ML · Mar 29, 2010

Sorry Brian, the stanchion will not easily "wear in" the bush, one is hard chrome the other a sintered oil bearing surface. I tried for a a year of riding on all sorts of roads to wear it in, but nothing changed. Not unusual these days with lack of quality checks in after market parts, however if you are patient and careful you can ease down the internal of the bushing with a engineers line reamer. The crude alternative is to rub it with emery cloth, it will work, but you must absolutely clean with solvent the bush surface and rub it throughly with a rough rag to pick up any abrasive. Take it slow and easy, check frequently and use very light oil in the process.

Mick

bpatton · Mar 29, 2010

Brian,
What was the fit of the bushings like in each slider? Sometimes you can mix and match the bushings because they are all slightly different and so are the sliders. If the tight bushing was a really snug fit in the slider and a nice fit on the tube before it was installed in the slider you can take some of the material off the outside surface of the bushing. Press fit bushings like this 'crush' somewhat in that their internal diameter shrinks after being installed in the housing. This way you can leave the finish alone on the working surface, but it will only work if it's an interference fit in the slider and it's a sliding fit on the tube before assembly. QC on these bushings is iffy.

BrianK · Mar 29, 2010

No hope here? I can redo, but it's fairly discouraging....!

These were NOS bushings, by the way. From the way the paper washers in the rebuild kit had deteriorated with age, I'd say they'd been on the shelf as long as my Norton's been on the road.

Thanks all.

jseng1 · Mar 29, 2010

Here's the answer
turkite fork bushings

but expensive.

Jim S

BrianK · Mar 29, 2010

I guess I'm just still a bit perplexed that the friction that's obviously present between the stanchion and the bushing won't wear the bushing down enough to eliminate that friction eventually. Maybe the answer is, it will but it will take a long, long time?

I guess I'll remove the fork tube and reinstall the old bush.

swooshdave · Mar 29, 2010

BrianK said:
I guess I'm just still a bit perplexed that the friction that's obviously present between the stanchion and the bushing won't wear the bushing down enough to eliminate that friction eventually. Maybe the answer is, it will but it will take a long, long time?

I guess I'll remove the fork tube and reinstall the old bush.

I wouldn't put the old one in. Instead either try swapping the bushings from side to side or better yet re-read Bob's advice. It's solid. Take the material off the outside of the bushing, if you can.

What was the fit of the bushings like in each slider? Sometimes you can mix and match the bushings because they are all slightly different and so are the sliders. If the tight bushing was a really snug fit in the slider and a nice fit on the tube before it was installed in the slider you can take some of the material off the outside surface of the bushing. Press fit bushings like this 'crush' somewhat in that their internal diameter shrinks after being installed in the housing. This way you can leave the finish alone on the working surface, but it will only work if it's an interference fit in the slider and it's a sliding fit on the tube before assembly.

Who can forget this classic thread on forks and bushings? :mrgreen:

Just Forking Around

Coco · Mar 30, 2010

Different suppliers are all selling bushings that are sometimes out of spec. It took me three sets last time I ordered new ones to get them to fit properly. The last set I got were packaged by Domi Racer and they were not even close to fitting. I got them from Walridge and they quickly sorted me out with a proper set that fit. Maybe one of yours is out of spec?

jseng1 · Mar 30, 2010

I made them of course - I don't like fork sticktion - I like a smooth ride. And they do not wear the tubes like bronze does. I can't remember the type of turkite but I researched it and use the best for the application. Had to buy a bar of it and its not cheap.

I also use a teflon impregnated bushing for the lower bushing - its laid out in my race manual.

http://users.gotsky.com/jimschmidt/nortmanual.html

Jim S

BrianK · Mar 30, 2010

Beyond my meager skills, I'm afraid.

I put the old bush back in (after filing notches to accomodate the leak proof seals). It looked to be in fine shape, I only replaced it because I was "in there anyway" (a phrase that gets me into lots of trouble).

Now my all time least favorite job - bleeding brakes (brake, in this case). Hate it, hate it, hate it.

Flo · Mar 30, 2010

I was going to suggest cover the stantion in metal polish & running the bush up & down it, but it is too late now.
Wish you luck bleeding that brake, gave up on mine, but seems good now. It is a time facter thing, all them bubbles.

BrianK · Mar 30, 2010

Good idea Flo. I did something similar with the swingarm bushes way back when (valve grinding paste and the spindle, doin' the old in out and around.

I have learned the keys to bleeding:

1. Caliper must be higher than the M/C. I hang it via bungee to a rafter.

2. Pump the lever, hold it and bungee to the bar. Leave overnight.

3. Bleed and repeat.

4. Voila!

Still hate it!

swooshdave · Mar 30, 2010

Grinding paste and a porous bronze bushing just can't be a good idea.

BrianK · Mar 30, 2010

Wot, you missed that classic thread Dave?

Anyway, I did clean those swingarm bushes as best I could. No reaming facilities around here that I'm going to avail myself of, so not a lot of options beyond DIY as best Y can.

swooshdave · Mar 30, 2010

BrianK said:
Wot, you missed that classic thread Dave?

Anyway, I did clean those swingarm bushes as best I could. No reaming facilities around here that I'm going to avail myself of, so not a lot of options beyond DIY as best Y can.

I assume you now know that taking some emery cloth to the outside of the bushing would have been preferred?

BrianK · Mar 30, 2010

Not sure that would've helped this time around Dave. It wasn't the compression on the bushing that created the fit problem - it was like that when I put it on the stanchion BEFORE fitting into the slider. Shoulda known then, but I was hoping it would wear in in short order, til folks disabused me of that notion.

But yes, I'm learning! Sheesh, if I just learn from my own mistakes, I'll be a genius!

Woolant · Mar 31, 2010

Hi Guys
My twopence worth: I made mine from oilon, an oil impregnated synthetic bushing material, I made them slightly oversize OD and undersize ID, then installed them into the legs. I then truned a wooden dowl to .5 mm smaller then the ID of the bush with a spigot on one end to go into a Battery drill; the other end I slit about 50mm down the centre. I then wrapped a med wet and dry strip around the dowl which is held by the slit. Slowly ream the bush using CRC as a lubricant until the tube slides nicely full length of travel. I then left the bushes soacking in fork oil for a few days as oilon expands. I then repeated the reaming process. I Have been riding the bike for a year now, the Forks are perfect. Incidently, I made the top bushes longer to act as bump stops and the fork Tube Sliders in the exact same manner.

Cheers

Tintin · Mar 31, 2010

jseng1 said:
I can't remember the type of turkite but I researched it and use the best for the application.

Most likely T47 which is bronze-filled PTFE for use in mineral oils and similar lubricants. If you really want the lowest possible friction put them into an acid solution for a few minutes after machining. This removes the bronze from the surface and leaves the PTFE only for the contact area.

Tim

daveh · Apr 11, 2010

jseng1 said:
Here's the answer
turkite fork bushings

but expensive.

Jim S

Hi Jim, would you be willing to share some more information with us here about your front fork mods? E.g.

the working clearance between your plastic bush ID and the stanchion?
do you have new fork legs?
do you machine the lower bush so that it is a tight fit on the stanchion and what clearance do you aim for between the fork leg ID and the lower bush OD?

Dave

john robert bould · Apr 13, 2010

Woolant said:
Hi Guys
My twopence worth: I made mine from oilon, an oil impregnated synthetic bushing material, I made them slightly oversize OD and undersize ID, then installed them into the legs. I then truned a wooden dowl to .5 mm smaller then the ID of the bush with a spigot on one end to go into a Battery drill; the other end I slit about 50mm down the centre. I then wrapped a med wet and dry strip around the dowl which is held by the slit. Slowly ream the bush using CRC as a lubricant until the tube slides nicely full length of travel. I then left the bushes soacking in fork oil for a few days as oilon expands. I then repeated the reaming process. I Have been riding the bike for a year now, the Forks are perfect. Incidently, I made the top bushes longer to act as bump stops and the fork Tube Sliders in the exact same manner.

Cheers

Oilite bush's need a Enginnering approch...install the stanchion and hold the slider in one hand and give stanchion a blow in a few place's with a hide mallet! Do not ream,emery ,,, believe my its the right way...and works....Oilite deform's easly ...and the smack with a mallet ..restores the alignment...been doing this for 40 years

New fork bushing stiction

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