Boxerworks.com

1979 r65

I am rebuilding my forks and have found a spring that I can not find in the fiche or other documentation. Should it be there? Should I keep it? The spring is 3 X 1.25 inch, it on the damper rod between the damper rod seat and the valve housing. I tried to post a photo, but I am having difficulties.

Thanks,

John

Sounds like an anti-dive setup. Popular a number of years ago. The idea was to allow for a change in spring rates as the suspension worked. It can make the ride harsher though...takes some tuning to get the proper action.

Kurt in S.A.

Thanks for the information. I still am having trouble uploading the photo, but a bit of detail. The damper rod and washers spacers valve is placed in the stanchion and a circlip holds it in. Then the short spring and damper rod seat "live" in the sliders. Kinda strange, but who knows what the PO had in mind.

John

John, the site won't accept photos anymore because the cupboard is full, or something. To post pics you need to have an account with a photo hosting site, upload the images, get the address URL and paste the link here. There are many free hosting sites - Google 'free image hosting' or some such, pick one and follow directions to post pics on forums.

I'm not quite clear where this spring is.

R65's had no toping out spring which on other forks sits inside the stanchion between the underneath of the damper piston and the top of the valve body. R65's had a rubber bush instead, Could a PO have replaced the bush with a spring ?

It's shown here in a generic diagram as the top out spring.

If the spring sits below the stanchion in the space marked A then it's the anti dive spring already mentioned.

barryh wrote:I'm not quite clear where this spring is.

R65's had no toping out spring which on other forks sits inside the stanchion between the underneath of the damper piston and the top of the valve body. R65's had a rubber bush instead, Could a PO have replaced the bush with a spring ?

It's shown here in a generic diagram as the top out spring.

If the spring sits below the stanchion in the space marked A then it's the anti dive spring already mentioned.

And, there's no reason to be certain that your forks are original R65 forks. You may have forks from another model (because of "upgrade" or repair), and they may have the top-out spring.

Barry, thanks for the image/ diagram. Yes the spring is in the area marked "A". MS the rest of the "bits" of the fork are correct for the r65 so I believe it is a r65 fork. The spring is too large to be used in place of the bushing. The question is should these be used? I really appreciate the knowledge and experience of the members since I am new to both BMW and motorcycling.

John

You shouldn't need an anti dive spring. R65 forks already have a stiffer spring rate than the early Airheads. Dive can be controlled in any case by the "air spring" that is the volume of air above the oil level. Oil level can be set between 20mm and 50mm above the damper piston top measured with a dipstick. 20mm will give the softest ride and 50mm will minimize dive. That change in oil level might not sound much but it makes a real difference.

I tend towards the 20mm level and still have no concerns about dive. My take on fork travel is what's the point of having X inches of travel if it's not almost all used sometimes under the most extreme provocation. That's what the forks were designed for. There is already an hydraulic bump stop that will take care of things should all the travel be used up. In that generic diagram the damper rod widens towards the bottom. As that tapered section enters the valve body it gradually restricts the oil flow and cushions the forks under full compression. In your forks this takes the form of the damper rod seat or top hat as it's known for obvious reasons.

When you reassemble the fork push the fork legs up to full compression so that the top hat enters the valve body and spin the leg around a few times to center things up before tightening the big Allen screw at the bottom.

That spring was popular for a few years, but fell out of favor when logic and bad experiences caught up with the fad.

People just added the spring on forks that may have already had stiction, but did it in a way that created the stiction by misalignment of the forks. They added in a new and negative factor. We had to do a lot of fixing of the mess created by owners and idiot mechanics.

What the owner considered excessive dive was gone/lessoned due to a new factor, stiction, not increased damping in a properly operating system.

Dive is a normal function and can be excessive for a certain weight, style and road condition. The whole idea was seldom properly tested that the fad just faded away, slowly.

I wouldn't suggest using it. Start off with forks that are in alignment, work properly and then make decisions about modifications.

Telescopic forks dive. Long travel telescopic forks dive more. As far as I'm concerned, all the solutions to this that all manufacturers have tried just reduce fork compliance when braking. As long as you have the correct spring rate for your weight (and correct air space as Barry discusses), I don't find any of the "solutions" to be a good idea anywhere but the track.

Of course, I'm usually riding an Oilhead with a completely different fork design that controls the problem without ruining compliance while braking, so I'm spoiled. It wasn't a problem on my /2 Earle's either.