Plastic disc in front forks

[dziadzu42]

A plastic ring in the front forks deteriorates with time. It is part  no. 31 42 1237 215 and was a topic in the Chris Harris rebuild video. (See below)It appears BMW no longer stocks them. Anyone know of a substitute or if any harm befalls the forks if used without these discs. I am pretty sure mine are gone because I found sludge at the bottom of the forks when putting in new seals.
https://www.youtube.com/watch?v=ymse3196ORY&t=159s

[tunnelrider]

This is commonly used instead of the softer red dissolving stop rings - I went through a couple of sets of super dissolving red rubbers before Barry put me on to these.  Motobins lists them as a part for R75 but they fit the R65 fork. I haven't done a fork rebuild since installing them a few years ago but haven't had a reason to.

Motobins part no. 29020

Barry - if you read this can you confirm it's the correct part please?

[mrclubike]

Does anyone know the part  number for the piston rings at Motobinsu

[Tony Smith]

Does anyone know the part  number for the piston rings at Motobinsu

Code: 29000    BMW: 31 42 1 232 059

[Barry]

I've had the Motobins parts in for over 10 years. They are much more durable than the original rubber rings.

[dziadzu42]

Thanks all.

[georgesgiralt]

Hello !
I complained at my dealer about the red goo they sell as a bumper.
The parts guy checked it's stock and saw he had two which dissolved themselves on the shell... He said to me he has a meeting with a BMW parts representative and he will told it's facts...
A few days back I saw him in the streets and he told me that BMW was aware of the problem and was searching for a new supplier/part. So maybe, one day, we will have something not hard as rock and not needing a change at every oil change...
Fingers crossed...

[Tony Smith]

I'll just repeat my earlier observation that the rubber ring is entirely unnecessary providing your fluid level is within co-eee of the correct amount - if so, the forks will hydraulically lock before the rubber stop is even touched. This is why 1,000s of R65s survived the decades when no replacement rubber was available at all.

[Barry]

I agree that in theory the forks should hydraulically lock once the two small holes in the damper rod pass below the valve washer but that assumes minimal leakage.  The original problem with my forks is that the leakage between the damper rod and the ID of the valve washer was far too much and I wasn't getting any hydraulic bump stop effect until I made a new valve washer with tighter tolerances.  It's very easy to feel if this hydraulic bump stop is working. Remove the springs and stroke each fork leg by hand. When it's working right you will feel a substantial increase in rebound damping over the last inch towards full extension.