FORK OIL

[Jeremy R65]

When I went over my R65 after purchase earlier this year, I changed the fork oil, replacing whatever was in there with 190cc of the pukka Aeroshell stuff from Motobins.  I was disappointed by the overall harsh ride and the clank from the front end over small road imperfections (of which we have an infinite number in UK).  I have improved the rear end by replacing the original Boge units with IKONs.  Now I have just changed the fork oil to a 5W made by Yamalube and this has made a noticeable improvement in how the forks move over small potholes etc. I think it is a better lubricant and has less "stiction".  I also bought some Fuchs Silkolene 7.5W which I may try out.

Now, my question.  Others have talked of reducing the oil level to 20mm above the damper rod to improve the "clank" - but how?  How can I get oil out from the top of the forks in small quantities? Or, if I drain it all out from the bottom again, how much do I put back in to get the 20mm lower level rather than the original 50mm?  Or is it trial and error with a dip stick?

Or am I just being dim witted...............

All comments gratefully received!

Thanks

Jeremy

[Barry]

Now, my question.  Others have talked of reducing the oil level to 20mm above the damper rod to improve the "clank" - but how?  How can I get oil out from the top of the forks in small quantities? Or, if I drain it all out from the bottom again, how much do I put back in to get the 20mm lower level rather than the original 50mm?  Or is it trial and error with a dip stick?
 

The nominal fill level is 35mm above the piston top but you can use plus or minus 15mm.  So 20mm above the piston top is the absolute minimum level. Given there is a very slight loss of oil over time due to leakage past the seals I use 25mm as a safe minimum fill level.  

The oil level really does make a perceptible difference as it governs the air spring effect so a lower oil level helps if the forks are prone to a topping out clunk.  I use the dipstick out of my car to measure the level and a syringe with a length of small bore plastic tube attached to adjust the level.

It wouldn't be hard to contrive a length of plastic tube with a fixed stop that ensures the end of the tube finishes 25mm above the piston top. Then you could overfill and remove the excess until it sucks air.

I find the oil level is very sensitive to fill volume and once sat down to calculate how much oil to add or remove to adjust the level by measuring the cross sectional area of the stanchion bore and subtracting the volume displaced by the spring. It came out at 1.8cc to make a 5mm adjustment.

I see no alternative to the dipstick method if you want to do it accurately given that such a small change in fill volume has an impact on oil level and given the difficulties of accurately measuring the oil added, not to mention ensuring you got all of the old oil out.

[montmil]

You may also be missing the OEM rubber-baby-buggy bushings that are prone to disintegrate over time in contact with the fork oil. Only way to determine if you have lost them, or if they have been replaced with the sturdier nylon bushing,s is to disassemble the fork's innards.
 :-/

[Jeremy R65]

Thanks Barry - I have bought a bit of hollow brass tube and will try the fill and 25mm level operation tomorrow.  Monte, I have not been inside the forks but did notice a small quantity of fine black powder in the oil when I drained it out, which may have come from the rubber stops; but no big bits as yet so I think I will leave well alone for now.  Best wishes, Jeremy

[montmil]

...Monte, I have not been inside the forks but did notice a small quantity of fine black powder in the oil when I drained it out, which may have come from the rubber stops; but no big bits as yet so I think I will leave well alone for now.  Best wishes, Jeremy

As did I when replacing fork oil in my then new to me '81 R65.

[sirwompus]

Maybe a bit off topic, but is anyone else using ATF in their R65 forks? I'm using it with no issues but wondered what the forum thought.

[Bob_Roller]

My Guzzi calls for ATF in the forks, works great in this application .

I've never experimented with fork oil in the R65's, just stayed with OEM 7.5 wt .

I've always had a BMW dealer close to the house, so I just use the original, if I didn't have a dealer close by, I would use 10 wt .

[Barry]

ATF is somewhere between typical 7.5W and 10W fork oil which means it would be too thick for me but some people do use it. One thing to said for ATF is that it has a consistent viscosity regardless who makes it while fork oil is all over the place.

The thing to do is when you find something that works look up it's  viscosity at 40 Deg C is and then you can reasonably substitute another fork oil that has the same viscosity at that temperature. Forget the designated viscosity such as 5W or 7.5W because it's largely meaningless when trying to compare different makes of oil or in some cases even the same make when Castrols dino 10W is thinner than their synthetic 5W.

ATF is something like 35 CSt @40 C  

I'm currently using  Silkolene 5W which is 22 CSt @ 40 C and even that's slightly too thick.

[montmil]

Just serviced the forks on my 1978 R100S while attempting to reduce / eliminate the "buckboard" damping that is rather annoying.

Drained out BMW OEM fork juice and refilled with Dexron III transmission fluid. Fairly thin juice.

I also pulled apart the bits at the top of the fork legs to check the fork springs. There are a few bits to remove before you can get to the springs themselves. What I discovered was a 2-inch section of 1-inch o.d. thick wall PVC pipe on top of the springs. Hum...

Added the refill quantity of 220 cc of fork oil, chopped away half the PVC and took off on a ride. Initial feel was much improved so I searched for bumps, cracks and road irregularities. Front end was behaving much better so found some really rough country roads and bumped up my speed.

Between the Dexron juice and the reduced fork preload, the "S" handles like a new bike. Have a ride this coming weekend heading north to an Oklahoma Airhead tech day. I'll push the bike even harder and see how the new fluid and reduced preload works out.

As always, your mileage may vary. Just my experience from messing with these Airheads.

[D Mann]

Monte at our last tech day I mentioned the what I think is excessive front end dive under braking. It was suggested that I add the PVC pipe to add some pre load to the springs. Did removing the spacers dramatically increase front end dive under braking?

I am curious because my front brakes squeal a lot under what I consider normal braking. Snowbum says this happens when we do not brake hard enough with the front. He seems to be right because if I brake hard the squeal goes away but man it feels like my nose will hit the road.    

[montmil]

Monte at our last tech day I mentioned the what I think is excessive front end dive under braking. It was suggested that I add the PVC pipe to add some pre load to the springs. Did removing the spacers dramatically increase front end dive under braking?

I am curious because my front brakes squeal a lot under what I consider normal braking. Snowbum says this happens when we do not brake hard enough with the front. He seems to be right because if I brake hard the squeal goes away but man it feels like my nose will hit the road.    

My R100S has twin ATE calipers up front. After having to replace one of the caliper bodies due to poor care from a PO, along with new pads and a proper adjustment, the brakes are quite powerful.

My primary issue with the front forks was the harsh damping during 'sporty" riding. Having previously used the official BMW fork oil -which is a re-branded product that BMW, on occasion- changes suppliers, I went to the Dexron III and used the drain & refill quantity rather than the overhaul specs.

In my opinion the two-inch preload spacer was the problem. Well, that and the fork oil. Carving off excess PVC to provide a 0.875-inch preload spacer and with the Dexron juice, I'm able to be more precise in carving corners. Smoother fork action.

There is no serious diving under hard braking. The bike just sort of settles and we're good.

If you haven't already done so, you may want to try a little bit of anti-squeal grease on the backs of your brake pads. A little dab'll do ya.