New Member

[Odelljr]

Greetings, I am a new member and first time R65 owner and first time participating in an online forum so I hope I am doing this correctly. I have been a riding since childhood owned and worked on numerous brands though this this is my first BMW. I recently acquired a 1984 R65. Bike is clean and low milage (11,800) for whats that's worth. Usually I research the heck out of something before taking the plunge. However, I bought this motorbike an a bit of a whim knowing little about the brand and nothing of this model.
I have changed fluids put on new tires rebuilt front calipered and added new pads. Which brings me to the forks. I have read the tech Q&A on this subject along with anything else I can find but I am still having trouble sourcing the internal bits and pieces needed for a fork rebuild. Fork seals seem to be abundant but can anyone please share in detail where I may find the the other required parts or suitable replacements. I'm not have any luck with motobins?
Thank you. Scott, Franklin TN

[tiggum]

Greetings from Brentwood, TN.  That's a beautiful bike, so congratulations are in order.  I am returning a 1983 R65LS to life after its having been in storage for the bulk of its existence, so I can certainly understand what you're going through.  I will contact you separately through a PM and give you the name of a local mechanic who can be of assistance.  As for parts, I generally rely on Bob's BMW in Jessup, Maryland.

And Season's Greetings to you and yours,
Tom Martin (AKA here as "Tiggum")

[Barry]

Welcome, very clean looking bike.

The only internal fork parts that are likely to need replacement are the topping out bushes #24.  Although Motobins don't list them, they do have a part that will fit.

Unless they are broken, it's not usually a good idea to change the damper piston rings as it takes 20,000 miles to bed them in. On top of that there are stories of replacement rings being too big.

[davidpdx]

Welcome to the Forum. I can't be of any help with your forks but you have come to the right place for advice. I have found this to be the friendliest spot on the internet when it comes to asking questions.

[Justin B.]

Nice paint, enjoy her!

[Tony Smith]

I'd add to Barry's comment that you will frequently find damper piston rings missing - the usual reason for this is that people try to put the damper rods in from the top of the forks and damage one or more piston ring int he process.

The piston rings can be found in the parts list for the /7 series forks.


Oh, and damper rods are inserted into the forks from the bottom, not the top.

[Odelljr]

Thanks for the advise and support. I have located and purchased all oem BMW parts needed here in the U.S. I found the correct upper bushings and a set of the harder plastic ones so now I have a decision to make. Which to install?

[Tony Smith]

I found the correct upper bushings and a set of the harder plastic ones so now I have a decision to make. Which to install?

No decision to make really, the hard plastic ones do not disintegrate and therefore cause no problems in service.

The alternative is to fit nothing at all as in theory the forks will hydraulically lock before metal to metal contact at the end of the stroke -  for the 20 odd years that the blasted dissolving red rubber bump stops were not available most people simply did without.

As to the longevity of the hard plastic bump stops - i recently fitted early model K100 forks to my R65 - the plastic bump-stops were the only non metal part I reused.

[Odelljr]

Interesting. Here is what I received. Two distinctly different parts.
The one on the right is the required R65 part (#1 237 215). It is more slightly malleable and has a squared shoulder.
The one on the left is the alternative part (#2 000 384) that fits a myriad of other BMW /5/6/7.
Perhaps BMW has sourced another material or supplier?

[Barry]

Thank you for posting that picture. It's a very useful contribution to the forum.

The original bumpstops that disintegrated were in my case black rubber and there were more recent reports of the genuine BMW part supplied being red rubber which disolved in no time at all. It does look like BMW have sourced another supplier which may perform better.  I would fit the softer version unless you are confident of the hydraulic stop being effective. Mine was practically none existent because of leakage between the damper rod and bore of the damper valve washer.

Here's how the rebound damping and hydraulic stop on full extension is supposed to work:


As the forks extend the damper piston forces oil back into the lower fork leg.  The valve washer drops and seals against the valve body and the oil can now only pass through a small 3mm hole near the top of the piston damper rod. This is the rebound orifice. The area of this hole is smaller than the area of the compression damping holes by a factor of 3 resulting in approx 3 times stiffer rebound damping relative to compression. That figure is typical as rebound damping is always substantially stronger than compression damping. During the last 25mm or so of extension this 3mm hole drops below the valve washer so there is nowhere for the oil to go except by leakage past the washer and to a much lesser extent past the piston rings. This is meant to be the rebound hydraulic bump stop and its efficiency will depend on the leakages mentioned. Variability here may explain why some owners have problems with topping out clunk and others do not. In my case the area of leakage past the valve washer was twice as much as through the rebound hole proper so there was very little effective hydraulic bump stop effect. In making my own valve washer I reduced the washer to piston rod clearance to cut the leakage in half and this eliminated the topping out noise.

When the thicker chamfered valve washer was introduced the washer to piston rod clearance was reduced which reduced leakage and therefore improved the rebound hydraulic bump stop so your later forks may be fine in this respect.  The easy test is to stroke the fork leg by hand with the spring removed. You won't feel much in the way of rebound damping until the last inch of travel when resistance should increase substantially. If it doesn't your hydraulic stop is not working as it should.

[andrelitinsky]

Wonderful looking bike. Mine looks the same!