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Hot Topic (More than 10 Replies) Does my damper rod assembly seem odd to you? (Read 4207 times)
nhmaf
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Re: Does my damper rod assembly seem odd to you?
Reply #15 - 06/19/13 at 22:16:05
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OK, I have some measurements - be aware that there might be some wear involved, and my garage lighting isn't quite as good as I'd like it to be.   I used a set of dial calipers which I also use for reloading ammunition, so all measurements are in units of inches, to the thousandths place:

Damper Rod Diameter (External, checked 3 places) 0.630 Inch

Valve washer (white plastic washer)
Thickness: 0.155 Inch
Inside Diameter: 0.635 Inch
Outside Diameter: 0.945 Inch

Valve body (top half):
Inside diameter: 0.785 Inch
Valve washer recess Depth: 0.170 Inch  (Yes, the recess is just slightly deeper than the thickness of the white plastic washer)

The "drilled washer" with the (8) holes in its body:
Inside diameter: 0.700 Inch
Outside diameter: 1.172 Inch (external edge has uneven ridge, possibly from wear?)
Thickness: 0.082 Inch
Hole diameter (approx): 0.115 Inch x 8 PLACES
Drilled holes are centered about the center of the "washer", with opposite drilled hole centers 0.900 Inch apart.   So, when the drilled washer is in contact with the white plastic valve washer (and I can verify this from bright wear marks on the metal washer, the white plastic valve washer covers approximately 50%-60% of the area of the (8) drilled holes. (.ie, the holes are slightly more than half blocked off).

The damper rod has QTY (1) 0.110 Inch DIA hole drilled through its tube from outside to inside (but not out the opposite side) centered about 1.010 Inch below the bottom of the piston with the piston fixed to the rod/tube.   The damper rod has QTY (2) 0.180 Inch DIA holes (drilled through and through) located approximately 1.300 Inch from the bottom end of the rod/tube (the part which sit into the base support).


My rubber rings, new plastic valve washers, and new drilled wasahers should be available for me to pick up at MAX BMW on Thursday, so I will start to put things back together - let me know if you need anything else measured before it is too late!!
Cheesy
  

Airhead #12178   BMWMOA #123173  BMWRA #33525  GSBMWR #563  1982 BMW R65LS  1978 BMW R100/7 1998 Kawasaki Concours
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Barry
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Re: Does my damper rod assembly seem odd to you?
Reply #16 - 06/20/13 at 02:20:43
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Mike, 

Thanks, that's brilliant,  I'll knock out some drawings comparing old and new valve body assemblies when I get chance.  In the long run it's going to be important to have the dimensions of parts that are no longer available.
  

Barry Cheshire, England 79 R45
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Re: Does my damper rod assembly seem odd to you?
Reply #17 - 06/22/13 at 16:00:44
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Using the data that Mike provided I've done a comparison between the original damper valve body components and the revised items.

The valve washer has been increased in thickness and the clearance between the washer and the damper rod reduced The vertical movement of the valve washer within the valve body recess has been reduced to half of the previous amount.


Comment:

This is all as expected. The reduction in clearance between the valve washer and stanchion will reduce oil leakage past the washer and increase rebound damping particularly over the last inch of travel. This was done to provided a stronger hydraulic bump stop effect in order to try and eliminate topping out clonks.

The vertical travel of the washer is reduced by half. The washer moves up under fork compression allowing a relatively free flow of oil through the valve plate holes and down under rebound sealing against the valve body.  In the transition between compression and rebound there is a dead band while the washer is moving so the new reduced amount of travel will improve damping control.

The only surprise was the lack of a beveled edge to the top surface of the valve washer. Mike mentioned that approx. half of the area of the valve plate holes are covered when the valve washer is in the up position (forks under compression).  The service bulletin shows a beveled edge which would uncover some of that lost area improving oil flow through the valve plate.


Detail dimensions in mm with old original items in brackets.

Valve washer white plastic  (steel)
Thickness: 3.94   (1.48)
Inside Diameter: 16.13  (16.2)
Outside Diameter: 24     (24)

Valve body
Inside diameter:  19.94  (19.94)
Valve washer recess Depth: 4.55  (2.45)


There were no changes to the damper rod or valve plate dimensions.
  

Barry Cheshire, England 79 R45
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montmil
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Re: Does my damper rod assembly seem odd to you?
Reply #18 - 06/22/13 at 16:50:08
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Hope an administrator will add this thread to the FAQs Section. Very valuable information presented herein.
  

Monte Miller
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Does my damper rod assembly seem odd to you?
Reply #19 - 06/22/13 at 17:13:06
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This Topic was moved here from BMW Technical Q&A, Primarily R65 [move by] Bob_Roller.
  

'81 R65
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I'll give up my R65, when they pry my cold dead hands from the handlebars !!!!!
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Re: Does my damper rod assembly seem odd to you?
Reply #20 - 06/22/13 at 20:10:43
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I've taken some more measurements and will create some sort of drawing or update for Barry with the additional data -

I noted the bevel edge description in numerous sources, and, I thought that I could JUST barely detect a slight difference in edges of the valve washer on the used part that I took out, but the new valve washer that I bought I stared at for quite some time and couldn't detect a difference from one side or the other on either outer edge or inner edge.   I bought new bumper rings, valve washers, "drilled washer", and new piston rings.    I used the new parts with the exception of the new piston rings, which I might possibly return to MAX, but I wanted them handy in case I encountered a damaged ring, which I did not, and they appear to be still in good shape.

I've taken some more photos and will upload a PDF linked to this topic for posterity.

At the moment I cannot provide a ride report/update as something *ELSE* seems to have now failed on the bike - I suspect the 3 year old battery has died despite being left on battery tender over the winter.  The bike ran perfectly on my trip down to MAX BMW a couple weeks ago (round trip about 90 miles).  Since then it has just been on the lift, with wheels and forks off while I've been repainting the wheels, putting new tires on, replacing the forks seals and rebuilding the damper units, and adding fork gaiters.   Now that I've buttoned it all up for its shakedown cruise, it won't turn over.   At rest with ignition off, battery voltage reads 12.8V, but as soon as I turn the key on, the voltage drops to about 6V.  I'm checking for shorts, too.  Though I cannot imagine that I've pinched any wires anywhere -  Grrrrrrr.
  

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Re: Does my damper rod assembly seem odd to you?
Reply #21 - 07/07/13 at 14:23:06
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I will be doing a more thorough write up and appending to a thread in the FAQ section in a while, but thought I'd at least post up some pics here to show closure and provide breadcrumbs to anyone else in need of rebuilding their damper rod assemblies in the fork tubes.

this covers the "later" style R65 forks which have the (3) piece (includes a very stout spring) damper valve assembly.

Generally speaking, if you remove the sliders/lowers from the fork as part of replacing a leaking fork seal, just slide out the damper rod assembly base from the end of the fork tube and look for the telltale black "gunk" of plastic bits that signifies a disintegrated black plastic topping out bumper/bush inside the damper assembly within the fork tube:

Ugh!

OK, these are the parts you will need (or at least can buy, as some are No longer available) for rebuilding the damper rod assembly:


*IF* you are careful when removing the damper rod assembly, you *may* not need to get new wiper rings for the damper rod piston (those tiny piston ring things in the upper right corner of the picture) as they usually don't wear out, but can become damaged, bent, mangled, etc. upon either removal or re-installation, or if you've just been unlucky.   These are the most expensive parts of the rebuild list - they are almost $8 a piece and you need (3) for each piston (one in each fork tube)


This is what the re-assembled damper piston assembly would like like with replacement topping out bumper (red plastic ring which replaces the previously missing/disintegrated black platic ring in the first pic in this thread). and new valve washer (white plastic ring) and drilled washer (metal disk with 8 drilled holes in its outer edge).   I was fortunate and could re-use my original piston rings, though I did carefull clean everything and inspect for damage prior to assembly.


The "official" writeup will include more info, plus tips on how to get the $%^&@! thing back into its tube and compressing that @#$% spring!  

hope this helps!
Mike
  

Airhead #12178   BMWMOA #123173  BMWRA #33525  GSBMWR #563  1982 BMW R65LS  1978 BMW R100/7 1998 Kawasaki Concours
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