The New And Improved Unofficial R65 Forum V2
Technical Discussion => BMW Technical Q&A, Primarily R65 => Topic started by: quixotic on July 29, 2014, 08:26:50 PM
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When I go over bumps, I can hear a slight clunk. Vaguely metallic. Seems to be something that at least weighs a few pounds or that can inflict a few pounds of force on something else. Seems to be roughly in the direction of the throttle, but who knows? I can hear it with my helmet on up until about 30 mph/ 50 kph. I've spent quite a bit of time hitting stuff with a rubber mallet, while probing with a stethoscope, but it's still a mystery wrapped in an enigma. Nothing hiding in the headlight.
Any suggestions?
Thanks in advance.
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Forks topping out on rebound will sound just like that. If so you have 2 options - go heavier on your fork fluid or/and replace top-out rubbers that have turned to mush in the bottom of your fork sliders.
For what it is worth MIL-H-5606E is the correct hydraulic fluid to use in BMW forks - the R65 bible says 190mm on a refill and 195 on a dry fill - I use 200mm wet or dry.
The actual oil I use is an Aero Shell fluid - I went to the local oil supplier and they had a 20lt drum of it that was past its storage date - they gave it to me.
The correct oil does make a huge difference, you will find that some fork fluids (notably Bel-Ray in my experience) attack the rubber bumpers in BMW forks and rapidly destroy them.
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If the heavier oil doesn't eliminate the topping out clunk then the only option is to use some other way to increase rebound damping ideally independently of compression damping. One method is to reduce the clearance between the valve washer and damper rod.
If you get to that stage I have some dimensions for making a new washer.
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Have you done anything to the forks recently ??
Like replace springs ???
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Wow! Thanks folks! And thanks bmwr65! It seems every time I get in a pinch and I'm frustrated enough to sell the old beast, this forum pulls through with vital info that I never would've thought of. Makes me wonder how I ever survived before the internet.
Anyways, I'll have a look-see at those bump stops and report back. Maybe before that, I'll replace the fork oil and see if it makes a difference.
No Bob, I haven't replaced springs or done anything to the forks since I bought the bike last year. And I don't recall the clank when I bought it, so I think it must've snuck up on me and gradually became noticeable.
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I ordered the "buffer" (as listed in Haynes). Also listed as the "stop ring" (Clymer). Is that the magic item that I need?
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Here's a page from RealOEM.com, an online parts manual .
Item # 24 is what you need .
http://www.realoem.com/bmw/showparts.do?model=0363&mospid=51897&btnr=31_0297&hg=31&fg=42
I've used nothing but BMW fork oil and it dissolved the rubber stop as well, on my '81 R65, just a poor material was chosen for this part .
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Bob
I am desperately disappointed to hear that as ever since I shifted to my free can of Aero Shell hydraulic oil I have not had rubber bits "eaten".
Mind you using a rubber bumper as a stopper is poor engineering, they could have just as easily designed a system to progressively increase damping rate as the fork reached the limit of its travel, reaching full hydraulic lock just before mechanical end of travel.
BMW are a funny mob in my opinion, sometimes they do things in an amazingly complex way to achieve very marginal increases in reliability and on other occasions they take quick-fix solutions that condemn the owner to feed the machine "consumables". A good example of complexity is the throttle arrangements, and a good example of "quick-fix" is the stamped steel top bridge they used right up to the R65 when they finally designed and fitted a proper top triple clamp.
The general R65 fork design continued into the early K series and they just fiddled with it, never actually fixing the problems, then threw their corporate hands up and went to the Telelever. Go figure.
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When I got y '84 LS in 2010, I disassembled the forks to check them out, as the bike had sat for some time unridden .
I purchased new stops and the rubber stops / bumpers, were of a different material than the originals, don't know if they will survive any better than the old ones . :D
They are red .
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Here's a page from RealOEM.com, an online parts manual .
Item # 24 is what you need .
Thanks Bob. Actually, I found out about realoem just this morning, when I phoned up Shails (from Langley, BC).
I have to put another plug in for them. They're incredible. (I've more or less given up on bmw2valve and Anderwerks). Anyways, some guy answers the phone, and to make sure that I've got precisely the right part, he walks through the realoem site with me to arrive at the #24 part. Then a couple of other fork consumables that he thought could possibly need changing (eg crush washers). It took maybe 5 or 10 minutes total. And if the last time I ordered from them is anything to go by, I should have the items in less than a week.
Oh, and I went to the local bike barn and got Pro Honda 5W fork oil.
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Oh, and I went to the local bike barn and got Pro Honda 5W fork oil.
I'll bet you that it is way too light.
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It does seem to be on the thin side with 17 cSt @40C and 3.8 cSt @100C
That's very close to Motul 5W I tried and found a little too thin. Better too thin than too thick though and easy to blend in some thicker oil if needed.
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Should I try Pro Honda 10W, then? (I haven't broken the seal yet, so I can easily return the 5W). I guess I'd prefer to feel the pavement a bit more versus wallowing.
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The problem with fork oils is that the nominal rating of 5W or 10W doesn't tell you anything very useful. First of all it's the nominal rating at 100 Deg C which is nonsense for normal use as fork oil doesn't get that hot. 40 Deg C is much closer to reality so any comparison between grades and different makes should be made with a knowledge of the viscosity at that temperature. There are several charts available on the net that list viscosity figures at 40 C. What you'll find is there is a wide disparity of viscosities between makes of oil even when the nominal weight is the same.
For example
Honda 5W is 17 cSt @ 40 C
Silkolene PRO RSF 5wt is 26.7 cSt @ 40 C
The best advice I can give is choose a fork oil that is readily available to you in several grades and that you can find the viscosity figures for at 40 C. Then be prepared to experiment by for example mixing 5W with 10W. You can switch makes provided you know the viscosity at 40C. I found it easier to home in on the correct viscosity by starting too light.
For what it's worth I've found that viscosities in the range 15 - 18 Cst to be too light and anything over 26- 28 cSt to be too heavy. On that basis Honda 10W may be too heavy but it's a personal thing that you need to set a benchmark for through experimentation.
http://transmoto.com.au/comparative-oil-weights-table/
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For what it's worth I've found that viscosities in the range 15 - 18 Cst to be too light and anything over 26- 28 cSt to be too heavy. On that basis Honda 10W may be too heavy but it's a personal thing that you need to set a benchmark for through experimentation.
http://transmoto.com.au/comparative-oil-weights-table/
Hmm. Thanks for that. Based on the link and your past experience, I think I'll try mixing the 5w and 10w half and half and see how that goes.
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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).
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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.
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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.
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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)
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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.
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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.
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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.
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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.
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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.
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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.
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Motobins have them.
Alternatively have you read about Chasbmw turning the piston slot a little wider to accept the later type plastic wipers.
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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?
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When you reinstalled the springs, did you have to work against the spring, compress it to get the caps installed and secured ???
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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.
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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 .
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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 .
I'm not sure, but the springs in mine had the top half dozen and the bottom half dozen spirals side by side (ie, almost fused). Looks like they came out of the factory like that.
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If the heavier oil doesn't eliminate the topping out clunk then the only option is to use some other way to increase rebound damping ideally independently of compression damping. One method is to reduce the clearance between the valve washer and damper rod.
If you get to that stage I have some dimensions for making a new washer.
I think I'm at that stage.
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When you tested the rebound damping did you feel the increase as the forks approached full travel ? If not you need to accurately measure the clearance between the damper rod and valve washer hole. My original steel washers had 0.25mm clearance (0.010") The area that represents is 12.7mm2 which is almost twice the area of the rebound hole proper at 6.8mm2. I made up new nylon washers with 0.15mm clearance that reduced the leakage area to 7.6mm2 I also increased the washer thickness from 1.48mm to 1.95mm and bevelled the top edge. All of these changes mimic the later valve washers that BMW introduced except that washer was thicker still and used a different valve body with a deeper recess.
Get the valve washer leakage right and you will feel the hydraulic bump stop effect on the last bit of rebound damping and that will completely eliminate the topping out clunk.
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When you tested the rebound damping did you feel the increase as the forks approached full travel ?
I felt something that may have slowed down the rebound slightly, but it didn't really feel like a gradual hydraulic damping. More like a muffled click.
But I don't think that the clunk/rattle noise appears only when the forks are fully extended. Seems like it appears even on relatively minor bumps at fairly low speeds.
Snowbum mentions the following for post-81 bikes:
Another part of this bulletin was for fork spring rattling inside the fork tube. There was supposed to be a white nylon plastic spacer used on BOTH ENDS of the spring. Implied was that if one or both were missing, they were to be installed.
I almost suspect that this type of movement describes the sound I'm hearing.
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Wow. Elsewhere, this issue started a 6 year long thread:
http://www.advrider.com/forums/showthread.php?t=379398
I kind of like the advice in post # 51 (too much oil). At least it's easy to check.
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Probably explains this part in the parts diagram, but no part number available .
Reference item # 18 .
http://www.realoem.com/bmw/showparts.do?model=0364&mospid=51897&btnr=31_0296&hg=31&fg=42
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I made up new nylon washers with 0.15mm clearance that reduced the leakage area to 7.6mm2 I also increased the washer thickness from 1.48mm to 1.95mm and bevelled the top edge.
That kind of precision is beyond my capabilities. Have you ever thought of making these and selling them? I, for one, would pay some big bucks for them. Or would the diameters of the damper rods change a bit from bike to bike?
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I felt something that may have slowed down the rebound slightly, but it didn't really feel like a gradual hydraulic damping.More like a muffled click.
But I don't think that the clunk/rattle noise appears only when the forks are fully extended. Seems like it appears even on relatively minor bumps at fairly low speeds.
That information about the noise raises another possibility. The valve body is retained in the stanchion by a large circlip. On the very early forks there was no attempt to shim the valve body to prevent any vertical movement so the valve body could rattle up an down by a small amount. Several mods were done first to shim the valve body and later to spring load it. You need to measure how much play there is betyween the valve body and the circlip then select a shim to fit. You will see the shims listed in the parts fiche. Mine had 0.020" clearance so I made a shim to fit.
Snowbum mentions the following for post-81 bikes:
Another part of this bulletin was for fork spring rattling inside the fork tube. There was supposed to be a white nylon plastic spacer used on BOTH ENDS of the spring.Implied was that if one or both were missing, they were to be installed.
I almost suspect that this type of movement describes the sound I'm hearing.
That’s not applicable to our bikes. There are no plastic spacers for our springs. Be careful about advice based on other models of airhead forks because they are different. In the ADVrider thread for example even some of the knowledgeable guys will have no experience R65 forks specifically. Glad you liked post #51 though because that's me. ;)
There is another other option which is to replace the whole damper valve assembly with the later type that has the thicker modified washer. This is supposed to address both the valve body rattle and the valve washer leakage issue I couldn't find those parts in the UK but I believe they are available in North America. If you look at the online parts fiche you will see a change of valve housing and washer listed from 09/80.
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That information about the noise raises another possibility. The valve body is retained in the stanchion by a large circlip. On the very early forks there was no attempt to shim the valve body to prevent any vertical movement so the valve body could rattle up an down by a small amount. Several mods were done first to shim the valve body and later to spring load it. You need to measure how much play there is betyween the valve body and the circlip then select a shim to fit. You will see the shims listed in the parts fiche. Mine had 0.020" clearance so I made a shim to fit.
I think I'll try that. They're dirt cheap, so I'll probably get a good assortment (if Shail's has them in stock) to deal with whatever gap I encounter when I open the forks up again.
There is another other option which is to replace the whole damper valve assembly with the later type that has the thicker modified washer. This is supposed to address both the valve body rattle and the valve washer leakage issue I couldn't find those parts in the UK but I believe they are available in North America. If you look at the online parts fiche you will see a change of valve housing and washer listed from 09/80.
I see the U.S. stock on the valve housing has "ended", so I guess I won't be ordering that.
I'll probably also go from 7.5 weight to 10 weight oil. And maybe I'll try your #51 suggestion, too.
Thanks. :)
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I'll probably also go from 7.5 weight to 10 weight oil.And maybe I'll try your #51 suggestion, too.
I don't how you are measuring oil volume but I always do it with a dipstick. The spec. is 35mm + or - 15mm above the damper piston top. So between 20mm and 50mm. I find the difference that range makes is very noticeable and run towards the lower end at 25mm. You should experiment to see what works best.
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Shails doesn't have any shims in stock, and it sounded like they haven't had them in decades...if ever. So I was wondering if I could make my own out of brass. Lee Valley sells sheets of "half hard brass, which resists compression" in thicknesses ranging from 0.001" to 0.01". Is the shim area an area which takes the full weight of a compressed spring? And is it critical to get the inner and outer diameters of a shim precisely cut? (I guess even after having taken a fork fully apart, I still don't really understand the dynamics of the whole, and the functions of the parts).
Also, is the function of the shim to ensure that there is no space between the valve housing and the perforated washer, as well as between the valve housing and the circlip?
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Is the shim area an area which takes the full weight of a compressed spring?And is it critical to get the inner and outer diameters of a shim precisely cut?
The only time the shim would take the weight of the compression spring is when the forks are at full extension. I think brass would be fine. The dimensions should be exactly the same inner and outer diameter as the valve body. Don't make the mistake I made of making the inner diameter too small thinking it didn't matter as when you look at how the fork functions the lower top hat hydraulic bump stop enters the bore of the valve body on fully compression and you don't want it to catch on the shim.
I guess even after having taken a fork fully apart, I still don't really understand the dynamics of the whole, and the functions of the parts).
It took me some time to fully understand it. If you are going to solve this you have to get your head around exactly how the forks function. Do you have Microsoft Word ? I can send you a lot of information I've collected.
Also, is the function of the shim to ensure that there is no space between the valve housing and the perforated washer, as well as between the valve housing and the circlip?
The shims fits at the lower end between the valve body and circlip so yes it pushes the valve body hard up against the valve plate. I guess there is no reason you couldn't fit the shim at the top between the valve body and valve plate except it would increase the travel of the valve washer slightly. The distance the washer moves is a dead zone between compression and rebound damping so it wouldn't be ideal. It would be easier on the shim though.
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Do you have Microsoft Word ? I can send you a lot of information I've collected.
That would be great. Thanks. You can send it to ebedford at rdcounty dot ca
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Thanks for all the info, Barry. Very much appreciated.
I assume my symptoms would direct me more towards the shim fix than the nylon washer fix.
For the shims, would I press down on the perforated washer while everything is still on the damper rod, and then see if there's any space above/below the valve housing? Then fill that space with a shim and insert it between the valve housing and the circlip?
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For the shims, would I press down on the perforated washer while everything is still on the damper rod, and then see if there's any space above/below the valve housing?Then fill that space with a shim and insert it between the valve housing and the circlip?
The damper rod need not be inserted when shimming the valve body. Just insert the perforated valve plate and valve body together into the stanchion recess and fit the circlip. You can then check if there is any vertical play and measure it with a feeler gauge.