Unknown rattle/clunk near headlight/handlebar

[quixotic]

I've started pulling the forks apart while they're still in the headset clamps (based on Barry's advice in this thread: http://www.bmwr65.org/cgi-bin/yabb2/YaBB.pl?num=1345097314/10#10 ).  

I'm at the point now where I have to un-do the hex bolt just above the axle clamps.  Since I don't have the forks in a vice, I'm thinking that maybe I should put some 1/4" threaded rod through the caliper bolt holes and the fender bolt holes and tighten everything up with 1/4" nuts.  

Would that provide enough stability?  The torque spec's indicate that the hex bolt is under less than 30 foot/lbs of pressure.  Or am I missing some obvious way to hold things steady enough?  (I just don't want to risk twisting the forks in the yokes and then screwing up the alignment).

[Tony Smith]

Take out the fork top plug, assemble 2 or 3 longish 1/2" or 3/8" extensions with a 13mm socket on the end. Have associate turn the hex bolt whilst you hold the ratchet handle.
 
Very occasionally your damper rod will spoil this party by unscrewing at the top instead of letting the hex bolt go at the bottom. This is where an air wrench is handy, put spring back in, re-insert form top plug, apply air wrench to hex bolt.
 
In the absence of an air wrench I have done the following - buy a sleeve nut that fits the top of the damper rod and a length of threaded rod sufficiently long to enable you to wind the sleeve nut onto the damper rod, squirt petrol at the top of the damper rod to flush out oil, coat sleeve nut with Loctite RED - wind sleeve nut onto damper rod. Wait till loctite sets up and then have another go, if this fails, remove forms from bike and take to bike shop or engineering works and have them apply air wrench.
 
When you put the damper rods back together, use Loctite Green to secure the top (damper piston) to the rod. Don't take fright, although Loctite green is a very strong threadlock, it gives in pretty easily to a little bit of heat wjhen you do need to take it apart.

[Barry]

Very occasionally your damper rod will spoil this party by unscrewing at the top instead of letting the hex bolt go at the bottom. This is where an air wrench is handy....

Sure does, it's happened to me twice.  In the absence of an impact wrench I've managed to shock the hex bolt free by manual means. I think on some of the later airhead forks they used Loctite at the factory

Evan,

Did you carry out the suggested test in #17 of the thread you referenced above and repeated below? This is the critical test to know if insufficient rebound damping is the cause of your clunk. Together with intact topping out bushes the absence of an increase in rebound damping over the last 25mm of travel is the key that unlocks the mystery of topping out clunks. Took me several years to figure that out and it transformed the pleasure I got from riding the bike.


Before the damper piston hits the bumper, rebound damping should increase noticeably over the last bit of travel as the fork approaches full extension. When the rebound damping orifice which is positioned 25mm below the damper piston falls below the damper valve washer the volume of fork oil below the damper piston has no where to go except to leak past the washer. This provides a hydraulic bump stop effect and slows the fork over the last 25mm of travel.

If you stroke the forks by hand with the springs out this increase in rebound damping over the last 25mm of extension should be very obvious. If you can't feel it then either the fork oil level is low or the oil is too thin or there is too much leakage past the valve washer.  

You should also be able to detect this increase in rebound damping with the springs in place but the wheel and mudguard would have to be off to stroke one fork leg at a time.

[quixotic]

Evan,

Did you carry out the suggested test in #17 of the thread you referenced above and repeated below?

I'll try that later today.  

When I let the oil loose, there was a trail of black gunk associated with it.  (Whoops.  I guess the release of oil means that I can't do the test...though I still have oil in the other leg)

[quixotic]

Well, I took everything apart in one fork.  As mentioned previously, the oil was filthy.  However, the thick bumper washer was entirely intact and looked like it was brand new.

Having just bought the bike last year, I have no idea when the fork oil was last changed.  Could this possibly be causing the symptoms?  

And the three little scraper rings didn't have their gaps 120 degrees apart.  In fact the gaps were practically on top of each other.  Could that possibly contribute to the issue?  

Anyways, tomorrow I'll try Barry's #17 suggestion and see what happens.  Hmm.  Actually, now that I think of it, I'll have new oil in there, so I wouldn't be able to know if old oil might have been the culprit.  And with the bike having only 23,000 km's on it, I can't imagine the valve washer being worn out.  

[Luca]

Loctite at the top and clean threads at the bottom of the damper tube will help ensure future fork work goes more smoothly.  As much as the BMW forks seem a PITA, at least they don't make the top of the damper with a special-tool receptacle as some Japanese bikes have done.

FWIW, my somewhat limited experience has shown that you can usually crack the lower damper bolts loose without holding the damper tube as long as the springs are still in place.

Did Shails include fork seals in their list of consumables?  At about $7-8 a piece they are surprisingly cheap for any brand of motorcycle.  Not a bad idea to change them while you have the forks apart unless you know they are relatively fresh.

[quixotic]

Did Shails include fork seals in their list of consumables?  At about $7-8 a piece they are surprisingly cheap for any brand of motorcycle.  Not a bad idea to change them while you have the forks apart unless you know they are relatively fresh.

I'm not sure what Shails might have included besides the bumper stops and some crush washers.  The package hasn't arrived yet.  However, everything I saw in there (except the oil) seemed in really good shape, so I'm just going to zip it up, put some new oil in and see what happens.

If I need to go back in there, at least now I'll be able to do it in half the time.

[Tony Smith]

http://transmoto.com.au/comparative-oil-weights-table/

Barry, an impressive find.....Castrol Fork Oil 5 seems to be on the money and is readily available world wide.

[Barry]

And the three little scraper rings didn't have their gaps 120 degrees apart.In fact the gaps were practically on top of each other.Could that possibly contribute to the issue?

I doubt it as a little leakage past the rings would be very small compared to the leakage past the valve washer.  Just to put it into perspective my original valve washers had an area of leakage equivalent to 12.7mm²  Also bear in mind the ring gaps will close up some when the rings are in the stanchion bore so even if they were lined up the leakage area would be tiny.

Damper rod forks in any case don't have a critical dependency on a perfect seal at the piston. Any leakage reduces the damping rate a little that's all.  Some early damper rod forks didn't even have rings just a close fitting damper piston so they must have leaked.

Not sure if this already got mentioned but on a slightly different tack There is a strong suggestion that replacement piston rings are incorrectly sized being too big which results in the gap closing up completely and excessive stiction in the forks so don't be tempted to replace the originals.  Or if you do check the gaps as you would with normal piston rings and be prepared to file the ends if needed. As a test for stiction insert just the damper rod and piston into the stanchion and stroke it by hand to feel the degree of stiction. If the rings are good the damper rod should all but fall down under is own weight. Less stiction the better as it all adds up with seals, dust seals and piston rings each contributing a little stiction before you even get to fork alignment. Low stiction forks are the goal and a joy to ride on.

[Tony Smith]

Related topic.
 
The three little metal "rings" on the damper rod assembly.
 
where can you buy them please cause I have had a wee accident with one of them.

[Barry]

Motobins have them.

Alternatively have you read about Chasbmw turning the piston slot a little wider to accept the later type plastic wipers.

[quixotic]

Well, I zipped everything up after verifying that the bumper stop was in good condition.  And I've got new 7.5 wt oil in there to about the right depth (an indicated 30mm with a dipstick).  

But the rattle/clank is still there.  Could it possibly be the springs knocking sideways against the stanchions?

[Bob_Roller]

When you reinstalled the springs, did you have to work against the spring, compress it to get the caps installed and secured

[quixotic]

When you reinstalled the springs, did you have to work against the spring, compress it to get the caps installed and secured

Yup, I used this homemade set-up, which I'm happy to report worked quite well.  And before I set it up, the top of the loose spring was right level with the top of the stanchion tube.

[Bob_Roller]

I was just wondering, if a previous owner had installed after market springs .

I installed a set of Progressive springs in my '81 R65 and they were about 1 inch, 25 mm shorter than the stock springs .

PVC spacers were included with the springs, to take up the difference in the shorter length replacement springs .