The New And Improved Unofficial R65 Forum V2

Technical Discussion => BMW Technical Q&A, Primarily R65 => Topic started by: dziadzu42 on September 29, 2018, 02:45:07 PM

Title: Plastic disc in front forks
Post by: dziadzu42 on September 29, 2018, 02:45:07 PM

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

Title: Re: Plastic disc in front forks
Post by: tunnelrider on September 29, 2018, 04:42:27 PM

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?

Title: Re: Plastic disc in front forks
Post by: mrclubike on September 29, 2018, 04:59:51 PM

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

Title: Re: Plastic disc in front forks
Post by: Tony Smith on September 29, 2018, 06:08:43 PM

Quote

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

Code: 29000    BMW: 31 42 1 232 059

Title: Re: Plastic disc in front forks
Post by: Barry on September 30, 2018, 04:37:06 AM

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

Title: Re: Plastic disc in front forks
Post by: dziadzu42 on October 01, 2018, 03:02:29 PM

Thanks all.

Title: Re: Plastic disc in front forks
Post by: georgesgiralt on October 03, 2018, 02:25:08 AM

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...

Title: Re: Plastic disc in front forks
Post by: Tony Smith on October 03, 2018, 03:19:14 AM

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.

Title: Re: Plastic disc in front forks
Post by: Barry on October 03, 2018, 06:37:03 AM

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.