Front Forks Maintenance

[Swimd01]

Does anyone have a good write-up / pictures for how to do a full maintenance on the front forks?

[Bob_Roller]

There is a thread about this, two postings down from this one, ' Fork disassembly for dual shock R65'S 'can't open it at work, so I don't know anything about it's content .

[Justin B.]

[movedhere] R65 Technical FAQ/Procedures [move by] Justin B..

[andrewwoodhall]

A disaster, or what? Whilst removing my front wheel I noticed the L fork leg had dropped a centimeter or so, making ot difficult to locate the axle. The leg would not compress, so I removed the front fender attatchments. The leg would not compress. Instead it came out completely from the upper tube, without any bottom stop being evident. What the heck is going on here and is it remediable. This is a new fork leg, installed for the previous owner by a third party BMW engineer?
Help much appreciated, please....

[georgesgiralt]

Hello Andrew,
Not exactly a disaster but could be...
The tube still on the bike has a threaded bottom end. Normally, when this tube is on the fork leg, there is a screw holding it in the leg; If you look on the "removed" one, you'll see the hole in it for the screw and if you look on the other fork leg, you'll see the screw.
IMHO, either the mechanic did not torque the screw at all or torqued it too much and ruptured it.
So if you put everything back properly, it will not be a disaster ;-)

[Barry]

It's not clear from the picture where the damper rod #25 is. Had the bottom screw #17 come out I'd expect to see the damper rod still located in the fork stanchion. Unless of course you have removed it


Other possibilities are the circlip #19 holding the damper valve body in the stanchion has come out or the damper valve piston (top bit of #25) has come off the top of the damper rod. It could have unscrewed or it's not completely unknown for them to shear off.  Unless you saw an oil leak prior to the leg coming off I'd say one of these latter possibilities has occurred.

If you haven't removed  the damper rod and you don't have all parts 19 to 24 on the floor then I say it's the damper rod piston that's become detached.

[andrewwoodhall]

Hi, and thanks for responding. No leak prior to event. Nothing yet removed. The fork leg came off the stanchion exposing the spring. I have not investigated further. Also, the first sign of the problem was total lack of compressibilityof L fork leg as I tried to align axle; it hit a hard, metallic stop internally. I rode the bike for 9 event free miles 2 days before..

[Barry]

Your first step might be to remove the large circlip in the bottom of the stanchion (if it's still there). The damper valve assembly should then fall out and you can see if the damper piston is still inside. If it is it might be canted over and jammed which would explain your symptoms.

Also look down inside the fork leg and tell us if you see the damper rod which is a thick walled metal tube 16mm in diameter and threaded at the top. If you can see those threads then the damper piston has become detached and as in above paragraph, may be jammed inside the stanchion.

[andrewwoodhall]

Thanks, Barry. I'll check as suggested. I'll report findings...

[andrewwoodhall]

Well, No circlip in evidence at the bottom of the stanchion. Confirm the allen bolt is  present in the bottom of the leg. I can't figure out what would stop the leg dropping off the stanchion in normal use!
Photos herewith...

[Tony Smith]

The damper rod (25 in photo) if it still exists, will still be firmly bolted to the sliding part of the fork that is now laying on the ground.

Looks to me that most likely the circlip at the base of the fork tube was not installed correctly and as that is all that keeps the innards "in" you have the situation pictured.

To the OP, unless there has been some serious, even bizarre, skulduggery you have an easily fixed problem.

Shine a torch down the fork leg that fell off and I suspect you will see the 13mm top of the damper rod. You will need a socket and extension on this and a suitable allen key at the base of the leg to undo the bolt that goes into the bottom of the damper rod. If you have an air wrench - use it on the bolt as it gives you better chance of undoing the bolt rather than the top of the damper rod.

If the top comes off the damper rod you will need to clean the threads with brake cleaner and then use Loctite green and put it back. Once the loctite sets up you can have another go at the real target - the bolt at the bottom.

When you get it all out, take photos and post them here.

[andrewwoodhall]

In above
Pic. 1 looking down the fork leg
Pic. 2 bottom of the stanchion..look no circlip
Pic. 3 lookin up into the top of the stanchion..

[andrewwoodhall]

Thanks, Tony. Your diagnosis seems to check out so far...

[Tony Smith]

Sorry I missed the second photo sequence.

100% either circlip not seated correctly on assembly or simply forgotten.

Get the bolt in the bottom of the slider out, inspect all parts for damage (unlikely) and put it all back together with a correctly installed circlip and all will be well.

[Barry]

Well at least you had the simplest cause of failure. When the big circlip goes back in be sure to get it the right way around. They are usual stamped out so have a slightly rounded edge on one side and a sharp square edge on the other. You want the sharp edge facing outwards so it locates nice and securely in the groove.

You haven't mentioned the year of this bike so the damper valve assembly might not be exactly as the diagram above which is the earlier type.  Later ones had a shorter sprung valve body.