The New And Improved Unofficial R65 Forum V2
Technical Discussion => BMW Technical Q&A, Primarily R65 => Topic started by: quixotic on June 26, 2015, 10:22:15 PM
-
I already took my forks apart last year, so I know it's not the disintegrating bushing culprit. But I came across the following thread, which notes that a lower fork oil level solved the problem...at least in that poster's case (on a 1980 R80). I think I'll try it, but was just wondering if anyone else already had tried it, and if so, was it successful? And if successful, is there a particular oil volume or level which seems to work?
http://www.advrider.com/forums/showthread.php?t=921191
-
The R65 fork damper components were changed on a regular basis to try and get rid of "clunking" afaik they never succeeded. I do know someone who fitted R80ST forks and howled with rage when he discovered that they clunked too.
In my experience the best way to reduce clunk is to use the right fluid. It is fluid viscosity that does the damping, not fluid "weight". For example Motul 7.5wt fork fluid will give you less damping than Castrol 5wt, in fact as far as I can determine you may as well use water as Motul 10wt.
For my wife's bike Castrol forkfluid 5 is too light and fork 10 is too heavy - a 50-50 mix is about right. I weigh a bit mor ethan her an dI run straight castrol fork 10. Our forks still clunk, but less often and less annoyingly.
I once did the exercise of workign out what the hell the now obsoleted aviation hydraulic fluid originally specified was - for all intents and purposes it was Dexron I trans/hydraulic fluid, which kind of explains why castrol fork fluid works better than motul. (Hint, shake the bottles)
-
And one more thing.
Worn-out or missing piston rings on the damper rods will do it too. Remember to take them out of the BOTTOM of the forks and put them back in the same way to avoid damaging them.
-
This clunk you are experiencing, does it occur when riding off a kerb or across a pot hole or sharp edges. If it does then it's a topping out clunk as the fork reach full extension.
The cause is too much spring pressure or insufficient rebound damping or both. One solution is thicker oil but that increases compression damping as well which will produce a hard ride. You can help a little on the spring pressure side of the equation by running the minimum level of fork oil (20mm) which will reduce the air spring effect.
In that ADVrider thread mention was made of manually stroking the forks without the springs fitted so you get to feel the damping effect. That is a very valuable exercise. You should feel practically nothing on the compression stroke but rebound damping should be quite noticeable and most important of all as far as eliminating the clunk is concerned you should feel a substantial increase in rebound damping over the last inch or so of travel. If you don't feel that increase then the problem lies with leakage of oil past the valve washer and possibly damper piston rings although they would have to be very bad to make a big contribution to the problem.
The solution is a valve washer that has a little less clearance between it and the damper rod which reduces the leakage and allows the rebound damper orifice to do it's job.
-
This clunk you are experiencing, does it occur when riding off a kerb or across a pot hole or sharp edges. If it does then it's a topping out clunk as the fork reach full extension.
No. I get the clunk -- actually more of a clack -- when I go over any little imperfection in the road surface. Very similar to what the poster in advrider was experiencing, so I thought I'd try his solution.
I did just take out 10 ml's from each fork to see if there was any change. Nothing too discernible, so I may try it with another 10 ml's taken out.
-
In my experience the best way to reduce clunk is to use the right fluid. It is fluid viscosity that does the damping, not fluid "weight". For example Motul 7.5wt fork fluid will give you less damping than Castrol 5wt, in fact as far as I can determine you may as well use water as Motul 10wt.
I'm pretty sure I've got 7.5 wt in there. I see I have a bottle of 5 wt and a bottle of 10 wt (both Honda Pro brand stuff), so I'm pretty sure that I mixed the two last fall, when I had one of the forks apart.
-
I did just take out 10 ml's from each fork to see if there was any change.Nothing too discernible, so I may try it with another 10 ml's taken out.
Measure the level with a dipstick lowered until it hits the top of the damper piston. You can go down to 20mm of oil on the dipstick.
Tony mentioned that the damper valve assembly was modified over the years. The first thing they did was to shim the damper valve body to eliminate any vertical play where it is secured in the stanchion. This tends to eliminate rattling noises on coarse surfaces and small bumps.You will see these shims listed in the online parts fiche Next they replaced the thin steel valve washer with a much thicker plastic washer and increased the depth of the recess in the damper valve body but not by all of the additional thickness so the net result was to reduce the valve washer travel by half. This reduced the dead band in the transition from compression to rebound damping and tighter tolerances reduced the leakage past the valve washer. The final mod was to spring load a shortened version of the damper valve body. this was done to cushion the shock loading on the damper valve. All of these mods were done to reduce noise and although the fact that there were several iterations suggests at best they were not immediately successful, it may still be worth while retro fitting the later damper valve components.
-
Tony mentioned that the damper valve assembly was modified over the years. The first thing they did was to shim the damper valve body to eliminate any vertical play where it is secured in the stanchion. This tends to eliminate rattling noises on coarse surfaces and small bumps.You will see these shims listed in the online parts fiche Next they replaced the thin steel valve washer with a much thicker plastic washer and increased the depth of the recess in the damper valve body but not by all of the additional thickness so the net result was to reduce the valve washer travel by half. This reduced the dead band in the transition from compression to rebound damping and tighter tolerances reduced the leakage past the valve washer. The final mod was to spring load a shortened version of the damper valve body. this was done to cushion the shock loading on the damper valve. All of these mods were done to reduce noise and although the fact that there were several iterations suggests at best they were not immediately successful, it may still be worth while retro fitting the later damper valve components.
Thanks Barry. I'll look into this further, since when I disassembled the fork last year, I didn't recall seeing any parts which weren't totally stock from 1979.
-
I had a look on Max BMW. Looks like there's a valve body that got updated in September, 1980, as well as a variety of shims ranging from 0.1mm to 0.5mm thicknesses. Am I barking up the right tree so far?
As well, there is an updated gasket ring (or fork seal) that fits in the top of the slider body, but I suspect that that's not what I'm looking for...or am I?
-
As well, there is an updated gasket ring (or fork seal) that fits in the top of the slider body, but I suspect that that's not what I'm looking for...or am I?
That's the fork seal and not related to noise problems. What you will need though unless already replaced is the red topping out bush 31 42 1 237 215.
I had a look on Max BMW.Looks like there's a valve body that got updated in September, 1980, as well as a variety of shims ranging from 0.1mm to 0.5mm thicknesses.Am I barking up the right tree so far?
Shimming the valve body is the first step but only if it actually needs shimming. The valve body is retained in the bottom of the stanchion by a large circlip. You have to check if there is any up and down play in that arrangement. I had 0.020" and fitted a shim to eliminate that. The cost is negligible except for time and for me it cost nothing because I made the shim. It's worth pointing out though that this is only step one in improving the damper valve and if you intended to go to the latest version of the sprung valve body then shimming becomes redundant. Part of the reason they introduced the sprung valve body was to eliminate the need for the factory to select shims during the assembly process.
This PDF service bulletin attached below describes what was done and provides the part numbers. The diagram is hopeless unless you already know what you are looking for but you'll see the text describes the thicker valve washer I mentioned earlier and the deeper recess in the valve body to accommodate it. The seeger circlip has spring tabs attached which effectively spring loads the valve body and eliminates the need for shims. They mention a hardened valve plate (the large washer with lots of holes in it) of the same dimensions. I've never understood the need for that to be replaced and have seen no signs of wear on my original plate.
I should point out that I haven't fitted the new parts because they were not readily available in the UK. If only we had a MaxBMW. I made my own although not to the same dimensions as the upgraded parts because at the time I didn't have those dimensions. I just adopted the concepts and the changes shown in the drawing below cured the problem.
-
Thanks Barry. Looks like Max BMW no longer has the valve housing, but Engeland Moto does: http://www.engelandmoto.com/bmw-valve-housing-r80-gs-part-31422301885.html
It says it's for an r80, but the Max BmW site seems to indicate that the above unit will work for the r65 and r45's (part # 31 42 2 301 885). I haven't checked all of the parts yet, but Engeland Moto has the improved circlip also.
Is the improved "damper tube mount" necessary? It seems to be the only part which is significantly more expensive than the other parts.
-
That damper valve body is not the correct one. It's a later type that use a coil spring to pre-load it in the stanchion. It could be made to work but you would also need the spring and it's carrier. I can find a diagram to explain that if you need it. It would be very simple to modify the existing damper valve body by machining the recess a little deeper. Somewhere I have the dimensions needed which were kindly provided by another member here. I'll try and find it.
The damper tube mount is the hydraulic bump stop for full compression. Although the diagram doesn't show it clearly the bump stop is tapered so that as it enters bottom of the damper valve towards full compression it gradually produces a hydraulic lock to prevent metal to metal contact and shock loading. In practice it's very difficult to get the forks to full compression so I wouldn't worry too much about it.
The explanation of the comment must be that the deeper recess in the top of the damper valve would allow the top of the bump stop to interfere with the valve washer. I'm a little surprised that it would but It's very simple to check this when you have the forks apart and if it is a concern you could cut a few mm (the minimum amount needed) off the top of the bump stop - ideally in a lathe but it could also be hacksawed of and trued up with a file.
-
Thanks again. My hunch is that, given the difficulties of fiddling with the valve body, my best option might be to initially try shimming.
In the diagram above, what would be the optimal travel distance?
-
In my drawing above I have retained the original valve body but shimmed and replaced the original steel valve washer with a plastic nylon washer of my own manufacture that had the different dimensions as shown. The hole in the washer is smaller by 0.1 mm or .004" to reduce leakage and increase rebound damping. The washer is thicker by 0.47 mm to reduce the travel from 0.97 mm to 0.5mm or approx. half.
I was subsequently given accurate dimensions of the the BMW supplied modified washer which was 3.937 mm or 0.155" thick and the recess in the valve body was 4.5466 mm or 0.17 mm deep giving a travel of 0.6096 mm.
So I had a little less travel but close enough. My washer bore size at 16.2 mm is slightly bigger than the BMW modified washer at 16.129 mm but that's also a very small difference.
-
I may also start putting 10wt oil in there. I know it'll be a bit harsher, but my daily driver is a Miata with tires at 40 psi, so I might not notice the difference.
-
I may also start putting 10wt oil in there. I know it'll be a bit harsher, but my daily driver is a Miata with tires at 40 psi, so I might not notice the difference.
Before you get too deeply into the depths of your fork internals I really would look at what fluid you have in them.
Bluntly, fluid weight has F'all to do with the fluid's viscosity and it is viscosity that does the damping bit. For the minimal amount of money involved by a bottle of Castrol fork 5 and Castrol fork 10 and give your forks a 50~50 mix of both. I will be seriously surprised if most of your clunk problems do not go away.
Having said that Honda fork fluid might be exactly the same, but neither I nor you know that and that makes comparing "apples with apples" impossible.
Why do I bang on about Castrol fluid? Because I went through what BMW, Snowbum et. al. recommended and it was the one i could buy locally and having used it, I know that it works well.
BTW Snowbum has some interesting (and mostly accurate) things to say on the relative viscosity of forkfluids and how to calculate VI from the less than helpful figures published by some manufacturers.
-
For the minimal amount of money involved by a bottle of Castrol fork 5 and Castrol fork 10 and give your forks a 50~50 mix of both. I will be seriously surprised if most of your clunk problems do not go away.
Thanks Tony. Weird thing is though, that although we can buy Castrol products in Canada, all they -- apparently -- sell us here is engine oil and chain lube (just going off their website).
-
Well, I ordered the shims from Max BMW. But they no longer had the 0.1mm shim (I assume that's what "0,1" means). And Engeland Moto doesn't have them either. Therefore, I'm guessing that they're either exceedingly rare or non-existent. So I'm stuck with the 0.2mm, 0.3mm and 0.5mm shims that I ordered.
Given those restrictions, could I make my own out of brass sheets? I can get it in thicknesses ranging from .001" to .01" (.025mm to 0.25mm). The question then becomes: although the thickness can be precisely obtained, the other dimensions would be rather rough (ie, the inside and outside diameters of the washer-like objects). Would these dimensions also need to be precise?
-
Given those restrictions, could I make my own out of brass sheets? I can get it in thicknesses ranging from .001" to .01" (.025mm to 0.25mm). The question then becomes: although the thickness can be precisely obtained, the other dimensions would be rather rough (ie, the inside and outside diameters of the washer-like objects). Would these dimensions also need to be precise?
I measured the clearance at 0.020" between the bottom of the damper valve body and the circlip with feeler gauges then made my own out of shim steel but brass would be fine and much easier to work with. As far as precision on inside and outside diameter goes, although it's very fiddly to make such a small section shim don't be tempted to make the inside diameter any smaller than the bore of the damper valve body. It's easy to think the shim only has the clear the damper rod diameter but the the hydraulic bump stop enters the valve body at full compression and you don't want it to catch on the shim.
-
While I'm waiting for the shims to arrive, I may as well make sure that I understand what I'll have to do when they arrive. Would they go in between the valve ring and orifice plate (from Snowbum's diagram) so that the resulting free play between the two would be approximately 0.5mm's?
-
While I'm waiting for the shims to arrive, I may as well make sure that I understand what I'll have to do when they arrive. Would they go in between the valve ring and orifice plate (from Snowbum's diagram) so that the resulting free play between the two would be approximately 0.5mm's?
That's the wrong end of the valve body. Which Snowbum diagram as I'm not aware he has ever done one for R65 forks and a diagram of any other forks may well be misleading because they introduced a rubber washer in the position you mention which BTW it didn't really work long term anyway.
I'll go over the whole history of mods again because I'm concerned you might have an unrealistic expectation of what will cure the clunk. I don't have dates for when these changes were made in the early 80's but they are in the correct chronological order.
1.The earliest R65 forks had the valve body retained in the stanchion by a simple circlip with no attempt to remove free play due to manufacturing tolerances. In some but not all instances this allowed the valve body to move up and down enough to create complaints of noisy fork action.
2. BMW introduced the shims that you have ordered so the the factory could shim out the valve body free play on assembly.
3. To speed up production they introduced a seeger circlip with spring tabs that would pre-load the valve body on assembly and dispense with the need for shims.
Note: Eliminating valve body free play addresses only one potential source of noise in the forks. They went on to do further mods:
4. A thicker bevelled valve washer was introduced together with a deeper recess in the top of the valve body as detailed in the service bulletin. The aim of this mod was to reduce the valve washer travel by approx. half which provided better control of the damping in transition from compression to rebound. At the same time they reduced the clearance between the washer bore and the damper rod in order to reduce leakage during rebound damping. The effect this had was to increase rebound damping independently of compression damping and in particular to make the hydraulic bump stop effect function on full extension.
This bump stop effect occurs when the rebound damping orifice falls below the valve washer so that the oil has no where to go except to leak past the washer. If the leakage is too great then the bump stop effect will not occur.
With my forks that last two sentences are the absolute key to understanding how to eliminate a topping out clunk. In an earlier post I mentioned how useful it is to stroke the forks manually with the springs out so that you can feel the strength of the rebound damping and most importantly you get to feel the substantial increase over the last 1" of travel. In my experience if you don't feel that increase then there is no chance of eliminating a topping out clunk.
-
Sorry, I should have referred to Clymer or Haynes.
Snowbum terminology: valve ring and orifice plate
Clymer terminology: washer and valve washer
Haynes terminology: valve washer and perforated washer
The Clymer terminology seems to be the most unhelpful, so ignore that. The orifice plate is the same as the perforated washer. And the valve ring/washer sits below that. Do the shims then sit between the two?
I'm not sure what you mean by topping out. Is that when the front of the bike is totally unloaded and the forks are fully extended? If so, then that's definitely not the problem. I tend to hear the click/clunk when running over tiny little imperfections in the pavement.
-
Haynes makes most sense.
Here's a picture of the valve components minus the shim and circlip.
from left to right: valve body, my modified plastic valve washer, the original metal valve washer and the perforated plate.
the shim goes underneath the valve body and then the circlip goes under the shim.
The shim is the same OD as the valve body so In terms of removing any play there are only 3 places it can physically fit:
1. between the circlip and the underneath of the valve body.
2. between the top of the valve body and the perforated plate - that would restrict oil flow
3. above the perforated plate but that would also cause significant restriction to oil flow
So only 1. makes any sense at all. If anyone else is suggesting a different position then they are either talking about a different component or they don't understand how damper rod forks function.
Topping out is the forks reaching fully extension when the damper piston comes into contact with the rubber bush that sits between it and the perforated plate. If you are sure that the clunk is not due to topping out then maybe shimming the valve body (if it needs shimming) will do the trick but it didn't for me.
If shimming doesn't help then consider the plastic valve washer. Even if you do not need the additional rebound damping to prevent topping out there are two other reasons to fit it. BMW chose plastic to reduce noise because it would eliminate the constant metal on metal contact and secondly the reduced travel of the thicker valve washer gives better control in the transition between compression and rebound damping. And come to think of it there is a third reason. In the service bulletin BMW say that they have put a bevelled edge on top of the valve washer to reduces noise. I don't pretend to fully understand why that would help but it must be something to do with the dynamics of oil flow past the washer in that it reduces the masking of the holes in the perforated plate (see my drawing in an earlier post). I duly copied that feature in my valve washer.
-
So when I try the different shims between the circlip and the underside of the valve housing, what should I be measuring or looking for?
And I see that Max BMW has the updated plastic valve washers in stock. Would it be worthwhile getting a couple of those? Or would they be impossible to coax into the old valve housing? Maybe I could sand off some of the material to make it fit? (since the critical dimension -- the inner diameter -- should be the same)
-
So when I try the different shims between the circlip and the underside of the valve housing, what should I be measuring or looking for?
I assembled without a shim and inserted feeler gauges between the circlip and valve body to determine what thickness of shim to use.
I see that Max BMW has the updated plastic valve washers in stock. Would it be worthwhile getting a couple of those?Or would they be impossible to coax into the old valve housing?Maybe I could sand off some of the material to make it fit?(since the critical dimension -- the inner diameter -- should be the same)
It would be impossible to coax in the new washer as it will be thicker than the depth of the recess. You could certainly reduce the thickness of the washer and aim for it to be 0.6mm thinner than the depth of the recess (effectively what I did). Alternatively get someone with a lathe to increase the depth of the recess so that it ends up 0.6mm deeper than the new washer thickness.
-
Thanks Barry and Tony for all your help. I'll update the thread when I get everything assembled and out on the road again.
-
Problem solved! Even though it took me all day and a lot of cussing, I can now go over bumps without hearing the annoying clickity-clack.
I wound up inserting a 0.5mm shim in one fork and a 0.3mm shim in the other. And as for that nylon washer, I initially tried sanding it down, but then I saw that I had some spare 1/2" nylon drain plug washers. I just had to ream them out slightly, since their thicknesses were exactly what I needed (about 1.9mm). They didn't turn out to be perfectly concentric, but I gambled and put them in there anyway. Hopefully, they'll be just as robust as the BMW ones.
-
Good result.
I bet it will transform your enjoyment of the bike.