Fork Rebuild Stiction Help

[dswassy]

New member here, looking for some help.

I have an R80/7 and I am in the middle of of rebuilding my forks. I have noticed that I don't have any stiction, or very minimal when the forks are dry. I conducted the test with the fender mounted and the forks still on the bike. When the oil is in, the forks don't want to move much and barely rebound. Am I missing something? I assume if the tubes were bent, that stiction would occur when the forks are dry as well as filled with oil.

Thanks in advance. Happy to buy a six pack to anyone that can help me figure this out!

[barryh]

If you are conducting the "with oil test" without the springs being in then there should be very little resistance when stroking the forks by hand. On the compression stroke the damping will hardly be perceptible. Rebound damping should be stronger and much more easily felt.

If the springs are in then it's even more difficult to feel the damping working at slow compression speeds.

Either way, any strong resistance must mean there is a hydraulic lock taking place. The only solution would be drain the oil and dismantle to check the damping components are correctly assembled.

All assuming you have the correct oil volume.

If you can clarify whether the springs are in and whether the the wheel is in so that you are using the weight of the bike to compress the forks, that would help. Compressing the forks by hand with the springs in is very difficult without the weight and inertia of the bike.

[dswassy]

Thanks for the reply. The with oil test was done both while the bike was on the ground, and with each fork I individually while I was adding oil to each fork. As I pumped the oil, the forks got stiffer and stiffer. The springs were out, wheel was off.

I have taken apart all components and double checked everything is in good condition and installed correctly. Perhaps the oil I am using is too thick?

[gspd]

What viscosity oil are you using?

[dswassy]

I was using 7.5w but apparently the brand I was using is much thicker than it claims to be. Maybe that’s my issue. Going to try a thinner oil.

[barryh]

I can only speak from personal experience of using a 5W something similar to original BMW spec oil i.e. very thin. When pumping a single leg relatively slowly by hand, the compression damping was all but imperceptible while rebound damping was much more noticeable particularly over the last inch of travel before full extension when the hydraulic bump stop comes in to effect. If the top caps are in place the air space above the oil will be compressed when the fork is stroked and that is a surprisingly strong effect that produces several orders of magnitude more resistance than the damping. It makes a huge difference.

If your top caps were in place, you might want to try it without them.

[dswassy]

Thanks for the advice. I will give it a shot.

[jackonz]

I have the same bike and had similar problem, first the oil i used was too heavy even though it was a 5W oil it seems different brands of oil measure it differently, the fix in that was to use the genuine BMW oil.
Second issue that was a bit harder to fix was the fork brace that the front guard mounts on, it was tight and that interfered with the smooth action of the forks, I tested this with the springs out and no oil to make sure all was correct it took some bending of the brace to get it right.

[Bill Smith]

If it's truly stiction instead of thick fork oil, try this: During my rebuild, several sites recommended loosening the upper and lower triple clamps and the fender mount / brace and bouncing the bike by rocking it. This lines everything up and seemed to work well.

[dswassy]

Thanks all!