Triple tree fork tube nylon sleeve bushings.

#1
Some Minibikes have a nylon bushing sleeve inside the bigger diameter tube for the smaller diameter tube to slide in. A lot do have any bushings. It is just one steel tube sliding in another steel tube. Those are sloppy fits. It is most likely a 7/8" tube inside a 1" tube.
Who sells the nylon bushing sleeves?

I have some older front ends I want to up grade.

Thanks
Danford1
 
#3
Nylon sucks for this application, as it's too thin- unless you get larger neck, and then you might as well use superior bronze. Bronze oil light bushings are all over ebay.

I have never seen a mini bike come from the factory with nylon bushings. Maybe the new Chinese ones? Made the modification to bronze on several bikes. If you have a 7/8 or 1" neck, it's simple to go with a bronze bushing and 1/2" head bolt.

Nylon sucks there. Temp fix for slop at best.

Heck, go for broke and larger, and press in some Timken taper or balls on a larger neck.
 
#4
If you are hung on using a plastic I would look into delrin over nylon. It has much better properties and is even used in race car suspensions.
 
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#5
I know my speedway forks had a thin plastic bushing about 3.5 inches long on the top if I remember correctly I still have a new Pair I can post a picture of. I agree with Dave a Bush is better. When I just did my rupp continental resto I did not like the steel against steel so I made a bronze bearing bush with a ID of the inner tube and a OD machined to fit in a 1" stainless tube pressed on the bottom of the fork let. I also coated the inner tube with a Moly coating as similar metals sliding together usually results in Galling.
PICT0266.JPG P1030171.JPG
 
#6
I think I didn't describe things correctly somehow.
I'm not talking about the steering pivot joint with the 1/2" or 5/8" bolt.

I'm talking about the slider section of the front fork. One tube slides inside another tube 2-3" back and forth. It is the suspension travel portion of the front end where the coil springs are. Some minibikes DO have nylon or plastic sleeves there. I know for sure Rupps do as I had 3 of them :)

Here are a couple picts of the kind of front suspensions I'm talking about.
The older looking picture is an Manco Thunderbird front end. The sandblasted taken apart picture is from a Sears Best minibike.
It is interesting how companies have different designs of the same thing. The red Manco suspension has the bigger diameter tube on the bottom while the Sears has the bigger tube on top. Seems like the Manco design is prone to "stuff" getting between the tubes easily, especially water.
Neither front ends
have any sleeve bushings in them. I'm sure 40 years ago when things were new and greased up, they were fine. Now, with age and rust, things get sloppy.

Who makes the sleeve bushings besides Rupp? The Rupp bushings have to big of an outside diameter...
I'll have to mic the tubes to find out exactly what sizes they are but 7/8" outside and about 1" inside diameters are very close.


Danford1
 
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#7
Yeah, I wasn't following you either Danford. Got it now. Indeed, plastic inserts are used widely in rear shocks for example. On the larger bikes, like Powell, and Gote, bronze bushings are used to guide the telescoping front ends, and held in with tiny set screws on the outside.

You might be able to get some plastic from some old shocks. I wonder if you could procure some flat stock, then heat it with hot air over a form.
 
#9
Here are some photos of the heavier bikes I was referring to. Seeing some of your work, I know you could easily fabricate these.

Powell: (Bronze) P18.JPG

Gote: (Steel) Fork Assembly.jpg
 
#10
I measured my parts with a dial caliper. I came up with 0.931 and 0.875. Both dims are give or take a couple thou.
They aren't "perfectly" round from the years of wear.
"If" I were to find a sleeve bushing, it would probably be 0.9375 X 0.875 (15/16 X 7/8) ideally about 5" long.
I could drill out the bigger tube to 15/16" to fit the bushing if needed. I don't have a lath though so making my own isn't an option.

I just thought other minibikes had some sort of nylon/plastic sleeve bushings I could use...

Danford1
 
#13
"If" I were to find a sleeve bushing, it would probably be 0.9375 X 0.875 (15/16 X 7/8) ideally about 5" long.

Danford1
That is only 1/16" of clearance, so the bushing would be 1/32" thick, even thinner to allow for movement and out of round tolerances. Very thin for a bushing. If you could even get one it would likely wear out very fast. A better option might be to use one size thicker wall thickness tubing to make a tighter fit.
 

Gatecrasher

Well-Known Member
#17
You can buy the plastic bushings used in the Honda z50 and Kawasaki MT1/KV75 minitrail forks and make them work. I think they are made from UHMW (Ultra-High Molecular Weight) Polyethylene but may be mistaken. Whatever the plastic material used is, they last a long time.

Click on the link:

AFTERMARKET FRONT FORK FORKS GUIDE BUSHING SET Z50 Z50R CT70 XR50R CRF50F I FK09

The I.D. is 23mm (.906") but a slit is cut down the side to make them fit perfectly. These same bushings are used in many minibikes.

s-l500.jpg
 
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#20
That's good info.
I posted looking for the long bushing and a guy sent me arctic cat bushings that took the place of my MT1 long and short bushings

IMG_5503.MOV.mov


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The movie link didn't work, please try it again using the "Insert Video" icon.

The picture you posted looks like a Rupp fork bushing.
Those have to big of a diameter for what I need. The outside diameter of what I need is 0.931 or very close to it.

Thanks for trying though...

Danford1
 
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