Overhauling the front forks should be a part of any rebuild of a 36yo bike. The forks of the R65 are generally pretty solid however there is a rubber bump stop in the damper rod assembly which is well known for disintegrating. This results in sinister black sludge in the bottom of the slider (it also stinks). I think they usually disintegrate relatively synchronously although an example on Chris Harris’ YouTube channel where one leg disintegrated before the other which resulted in leg length discrepancy. This video was a massive help to me while rebuilding my forks and you should definitely watch it- thanks Chris!
The rubber bump stop was updated to a red version later (which apparently also disintegrated) and most recently to a clear nylon bush.
First drain the oil by removing the drain plug at the bottom of the slider assembly. At this stage I also removed the hex bolt from the bottom of the shaft. This is a 10mm hex bolt which is bolted into the damper rod. The problem with this bolt is that it is often over-torqued, and difficult to remove because the damper rod just spins in the slider. I used the Ryobi cordless impact wrench. This has proven to be a very useful tool and had no problems with this notorious bolt. The oil that came out of my forks was black sludge- a tell tale sign of rubber bump stop failure.
After the lower bolt was removed the slider can be removed (after the plastic dust extruder has been popped off. However before doing that, I turned the fork right way up and removed the oil filler cap from the top of the assembly. This was the only job so far which has required a second person. Mrs GFP helped to fish out the circlip while I pushed the plug down. When this has been removed the spring can be removed.
Then the stanchion tube was turned upside down and the circlip which retains the damper rod was removed. This allows the damper rod assembly to be removed and you should do this slowly keeping note of the order of the various components. Of course you may well be missing a bump stop! The oil seals can be popped out of the sliders using a big screw driver and taking care not to scratch the metal.
The components you should definitely replace are:
- Oil Seals
- Rubber o-rings on the filler caps
- Damper rod bump stop
- Possibly add shims under the damper valve
- Rubber boots
- Felts in the dust extruders
Reassembly is fairly straight forward although the order of the various components of the damper assembly can be a little confusing.
My fork springs looked in good condition and measured at 495mm unsprung which is within normal range according to Clymer so I reused them. Also, there was no up and down play in the damper rod valve with the circlip in place so I did not need to add a shim.
