Fork stop rings busting up?

[Tony Smith]

The 'Bins white nylon rings have enough 'give' to do the job. Unless you just really enjoy regularly taking apart the fork legs... I'd rather be riding than fettling.

Spec fork oil weight is 7.5 wt. A variance between brands is common so do not be mislead by labeling. Can get expensive trying different brands of the same so-called 'weight'. If you can source it, try Dexron III transmission fluid.

Monte

You are quire correct (although you didn't need me to tell you that) Dexron III is an exact replacement for the original specified fluid.

Problem is it is way too light unless you weigh about 40kgs and only ride on smooth autobahns.

There is a website that provides a viscosity comparison of various fork fluids, it is after all viscosity and not fluid weight that provides the damping. Interestingly there is one comparison I do recall - Castrol fork 5 has the same viscosity as Silkolene 15 weight (and Motul is not too far behind). Snowbum has some interesting (and at least mostly accurate) comments on fork fluids also.

[JJH]

Just another data point.  Last night I replaced the top bushing.  There was little trace of the original bushing.  I replaced them with a BMW sourced red bushing.  I did notice these bushings were very soft, but I had no experience with these bushings.  Before I added fork oil I had to take the forks back apart (a separate story).  On one side the bushing had turned to mush, the red licorice is a good description.  The other side was still intact but the bushing was soft and sticky.  The only thing I can think of is I did not remove all the cleaning solvent from the forks.  Since I am a chemist and have access to instrumentation, I tested the bushing and found that it is polyurethane (PU).  PU is an excellent choice for bushings,but...PU has MANY different formulations and is known to swell in certain solvents.  The formulation certainly could have changed, or a bad batch produced.  Anyway I am going to replace the bushings with teflon and hopefully that will solve the problem for awhile.

[Barry]

I'm no Chemist but I think The white bushes are also polyurethane. Quite firm though and I thought too firm to be ideal given every other fork uses a spring.

I could live with softer bushes if it meant they only lasted 5 to 10 years but yours went too far!

Good luck with the next set.

[tunnelrider]

Hmm, I wonder if a right bent fork tube has much to do with it                      
Mine sound worse than your JJH and they are BMW sourced red bushes as well.  
Just found the right fork tube is bent, that probably explains my problem.  Sorry to waste any time and unnecessary worries.
Symptom: jams in the clamps and hard to remove.
Cause: By me and numerous others.

Resolution: (not recommended but want to see the difference nylons make); reinstall with the harder white moto-bins bushes.

[Barry]

It's normal for the stanchion to be a tight fit in the clamps. I have a set of hard wood wedges made up to insert in the gaps. One test of whether the stanchions are bent is to carefully measure the distance between them top and bottom while rotating the suspect stanchion to see if they remain parallel.

If the stanchions are only very slightly bent by a couple of thou you can usually rotate them to get the most parallel position.

[tunnelrider]

Thanks for the tip on the hard wood wedges Barry, I have used a heat gun on both previous occasions to heat the clamps for removal/install (although I haven't done the 2nd install yet).

I found on the first install (before any dubious gravel riding by me) that the unbent fork tube had to sit higher in the clamps by maybe 3mm in order to install the front axle, so I'd say it's out by mm's rather than thou's.  Might have to invest in a new one when I'm feeling flush.....

So I'm thinking now that my rings busting up are a moot point without having a good fork alignment. Thanks for all of your guys advice though, it's been great, as always.

[Barry]

Differences in level between the fork leg lengths as indicated by the the alignment of the axle is usually the result of one of the topping out bushes having broken up so it's no surprise that you experienced that problem at least before replacing the bushes.

[SoloLobo]

Motobins parts arrived

[tunnelrider]

I've also put the Motobin's stop rings in, just like the ones above.  They feel about the same hardness as the BMW sourced red rings as far as I recall.  Had to re use a bent fork tube (out by 2mm), damn funds are tight, so they may not last well either.  But will use Castrol fork oil this time, eh Tony.

Thanks for the info guys.