Does my damper rod assembly seem odd to you?

[nhmaf]

OK, it was a long story which I will not get in to at the moment, but I had to replace the leaking fork seal to pass annual safety inspection this month in the R65LS.   I bought new seals and drain washers.  While I was in there I decided to look at the damper assembly as the ride had been different this spring - more than what I would attribute to a leaky seal.

As might be expected, the (formerly black) stop ring was disintegrated into bits.   But, I thought I recalled there also beingsome o-ring types of thingsin the channel of the piston assembly at the top.   Furthermore, this R65LS has a spring assembly (which is in (3) pieces) instead of what is generally shown as a single valve body from the old fiche - this seems like the replacement part 31422301885..  



So, I guess my main concern as I prepare to order more parts to get things working properly again, is are there other plastic rubber bits missing in this picture besides the disintegrated black plastic/rubber top bushing that I am assuming goes between the (2) piston rings to the right of the piston base and to the left of the perforated disk?

[georgesgiralt]

Hello
The two rings on the left should go into the ring holder on the left. (I recall they where 3 of them on my fork ?) Then the new rubber, then the perforated disc, then the white plastic bushing then the lower seat.
On my forks, that's it. You have a spring and another seat. They do not show on RealOem. So I'm puzzled.
What kind of modification your fork had  ?

[Barry]

Looks fine to me. You have the later sprung valve body which is supposed to be a good thing.

As Georges said you have to put the piston rings back in and 3 is the correct number. Don't put in new piston  rings unless they are broken as new ones are reckoned to be rubbish. Otherwise only the rubber bump stop is missing above the valve plate.  Can't see in the photo but if the the plastic valve washer has a beveled edge that goes to the top facing the perforated plate.

[georgesgiralt]

Hello !
Does any body have the part number for the valve body with spring ? Even if I select the latest R65, I can't find them on RealOem.
Thanks.

[Barry]

Georges

Part numbers are here but the valve body is shown as ended.

This has recently been discussed on the airheads list


http://www.realoem.com/bmw/showparts.do?model=0425&mospid=51641&btnr=31_0316&hg=31&fg=42

[georgesgiralt]

OK. The fiche you show is for an R100. I always thought the forks of the R65 where different.
And if I'm not mistaken, they are somewhat because the travel is different.
This is the reason why I asked  

[Barry]

The forks are not exactly the same but they are the same basic type with the same stanchion diameter so I believe the valve body will be the same.


I'll have a look at the other fiche sites to see if there is an R65 specific part.

[nhmaf]

Thank you both - I was careful in withdrawing the assembly from the fork tube but the rings had dislodged themselves from the piston as shown - probably due to all the bits of broken rubber getting caught up in there.

I've doen a bit more reasearch and found the BMW did experiment with the damper rod assembly, piston, and added spacers at the bottom between the valve body and the circlip on the end which keeps it all in the tube.   They were trying to stop the clicking and clanking noises that the forks were notorious for.   The R65 and R80ST forks also received some of these changes as they changed things several times between model years 1980 and 1983.   Presumably by 1985 they had standardized on the assembly using the (3) piece spring valve part as shown in the pictures, but now both the original piece, and the replacement piece, are No Longer Available.   So, treat yours with care, whichever version you have!!!

What makes things even more confusing is that the BMW microfiche drawings often show either the original parts stack up but not the later ones, or they show the all the parts - both old and new- together in the same drawing.   Since one doesn't venture into the damper rod area very often, it only serves to confuse one even more when looking up the parts in the drawings which do not matchup with what is installed.  

The (3) piston rings I've got seem to be OK - I've also read on Snowbum's website that the originals are better provided that they aren't broken, so I'll just carefully clean off the broken rubber bits and  re-use them.   Now back to the dealers to see if I can get some new rubber bumper rings...

Thank you for your help!
Mike

[georgesgiralt]

I changed the rubber bumper a few month back (less than 6) and they were available from BMW. they were red in colour and supple.
So I think it's still the case !

[Barry]

OK. The fiche you show is for an R100. I always thought the forks of the R65 where different.
And if I'm not mistaken, they are somewhat because the travel is different.
This is the reason why I askedCheesy

The R100 part number I suggested is correct.  Although the R65 diagrams don't show the alternative valve housing it is in the parts list below although still unavailable unless you are lucky enough to find one in stock somewhere.

http://www.maxbmwmotorcycles.com/fiche/DiagramsMain.aspx?vid=51892&rnd=04302013

[georgesgiralt]

Barry,
I've phoned my nearest dealer. None available, either at the factory store nor in any French dealer...
So my fork will stay with it's noise, clung and clank.... 30 years that I live with it.  

[Barry]

You don't need to live with as it can all but be eliminated by other means.

If the clonk is experienced when riding off the edge of kerbs or into pot holes then I believe it due to the forks topping out at full extension.

With only the inadequate rubber bump stop to cushion the clonk I assume the spring loaded  valve housing helped absorb the shock in the same way topping out springs do on almost every other fork. In fact if you check the part numbers the valve housing spring is identical to the topping out springs on other BMW forks. We can't fit them retrospectively as topping out springs would lower the ride height on our forks because the damper rod is too short.

There is another way. By increasing the rebound damping. The test that you have it right is to remove the wheel and fork brace and fender so that the legs can be stroked by hand independently. With the spring out you should be able to feel that rebound damping is stiffer than compression and most important for curing the clonk, there should be a significant increase in damping over last 20 - 25mm of travel before full extension. This is due to the rebound orifice falling below the valve washer so that the only path for the oil is leakage past the washer.

Problem is you can't increase rebound damping with much thicker oil as although that will help, the increase in compression damping will spoil the ride.

You can increase rebound damping over the last bit of travel more or less independently of compression damping by reducing the leakage past the valve washer. And you do that by reducing the clearance between the valve washer and damper rod. In fact the modified sprung valve housing also incorporated a thicker valve washer with this reduced clearance.

(Mike, if you still have your forks in bits any chance you could measure the damper rod diameter and the valve washer hole diameter)

It's only taken me 5 years and many trial to get it almost right but it can be done.

[georgesgiralt]

Barry, could you please stop speaking Chinese to me ?
I've lost my universal translator (Men In Black) so I'm puzzled at best  
The funny thing is that I had to replace the rubber ring (last time I changed oil I got small speck of hard translucent rubber in the oil, I think I told the forum about it). Since that time, the left leg make a different noise and it change with the temperature or the humidity ... or ....  At first I thought I forgot to torque some part or the triple clamp. Then I thought the 3 rings where not installed properly, then I decided to use the bike and let it sit until next oil change... and see what comes out.

[Barry]

Ok here's a simple mod.  


Buy the new valve washers and machine the recess in your existing valve bodies to the same depth as the unavailable part.

Mike, any chance you could also measure  the valve body washer recess and the washer thickness.

[nhmaf]

I had to do a bit of actual client work today, but should have some time to take measurements on Wednesday and report back here.

BMW shows various shims of very slightly different thicknesses which they initially specified to be placed under the (original, 1-piece) valve body, as they anticipated that part of the clunk was caused by excess clearance/end play in the damper assembly as parts wore-in or spring strength diminished.   These were only slightly successful, and the "final" accepted solution was apparently the split, 2-piece valve body with the spring in between, and apparently some changes in the rubber ring and alterations to some of the orifices in the damper rod.   I will say that my forks did sometimes "clunk" when they came to full extension, but we will see if it really stops with new replacement rubbers.

I tell you that short spring in the split valve design is pretty darn stout -