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I posted about my T140 forks up in the "What did you do to your bike today thread" https://www.britbike.com/forums/ubb...at-did-you-do-to-your-bike-today-join-in but I thought I would start a thread here, in the Triumph section, in the hopes of getting some ideas about how to proceed.

I have a mildly modified 1979 T140D and I have the engine about where I would like it--pretty much all stock, with just a few mild changes, such as MAP 9 1/2:1 pistons, retimed cams, JRC carbs (although I am in the process of changing over to Euro jetted AMAL Mk 2s), Kibblewhite valves and springs, and Boyer and Podtronic, and a low restriction muffler on the stock 2 into 1 header--and I am now turning my attention to the forks, which need help. I am concentrating here on getting them functioning better,. There is no question that installing a more modern fork will improve things, but I don't want to make a change like that on my street bikes--I want to continue with the standard period forks and get them working as well as I can.

The forks seem to suffer from the typical T140 complaint of failing to comply with smaller, sharp bumps that require the wheel to move quickly--seemingly because of either too much stiction, or too much high speed damping, or both. In other words, they "kick" or deflect off small sharp bumps, quite noticeably.
They seem to work fine, on slow roller type bumps, and in cornering and braking loads, which don't make the wheel move fast. This suggests to me the problem is either stiction and binding, or too much high speed damping, or both. I just did a mild initial tryout on a fork modification-- I just replaced the 97-4003 o-rings with a piston ring replacement I got from L. P. Williams in England (97-4003P) https://www.triumph-spares.co.uk/damper-valve-seal-conversion-1971-on-pair-97-4003p, and I replaced my 20 weight fork oil with Honda Proline 10 weight, 125mm from the top, fully collapsed with springs out, and I put them back together carefully to avoid binding and stiction. Unfortunately, I don't think I have improved them much because with the wheel still out, and either with both no oil (other than a little for assembly) and with oil in, each fork leg is still somewhat difficult to move and doesn't feel very free--about like they were before I put the piston ring replacements in. Then, I put them back together fairly carefully, in an attempt to get the forks centered on the axle and to avoid binding from that source--the grooves in the axles and the use of clamps on the axle on both sides are an unusual feature of these forks and could intorduce "pinching" the forks together, and binding, so it makes sense I thought to pay attention to that in putting them back together. Anyway, I guess I will figure out whether I made any real improvement once the snow melts in late April in Alaska. I have a lot of time yet to wait.

So, I am wondering, has anyone been able to do anything to these forks that improve their action on the sharp and little bumps, without degrading their low speed damping function? I am all ears at this point. I am guessing whatever is out there that works either addresses the stiction, or the apparent excess of high speed damping, but what do you have to suggest? I am guessing here that fixing the forks means modifying the damping somewhat. The trouble is, changing the high speed damping usually involves some kind of popoff valve that lets the wheel move quickly in small increments. Anyway, please let me know what you might have done?

Race Tech makes an Emulator for these forks, but I am not ready to try that yet, before I try less major modifications, since the complete changeover is fairly expensive and requires permanent modification of the damping rods, by turning the tops off in a lathe--no going back. Emulators modify older design damping rod forks in a manner to "emulate" the function of modern design cartridge forks, by doing away with the existing compression damping circuit and replacing it with a single stage popoff valve that kicks open on sharp bumps, and with an additional set of fixed damping orifices different than stock; the fork's original rebound damping remains in effect. This is all in a small aluminum damping valve body (like a suspension piston) that sits on top of the damping rod, under the spring. Emulators are adjustable for spring preload on the blowoff valve, and they offer alternative springs as well. The Triumph Emulator is FEGV 53301, for $179; the adapters that sit on the valve and space the spring away from it are FPEVAD3301P, for $19.99 or you can substitute a length of 3/4 inch PCV pipe; the Race Tech piston ring replacement is FPPR 273022; they recommend a .8 rate spring, which is FRSP S2643 080 and is (memory correct) about $160. I have used Emulators on my race bikes and they do improve these older design forks for sure, but I have never used them on a street bike so I am wondering if anyone has experience with them on the T140 forks, on the street.

Last edited by linker48x; 02/07/21 11:01 pm.
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Perhaps oil 125mm from the top is too much? Try just putting 190cc in and see how it goes?


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Hi linker48x, I have no answers but a few thoughts from my experience. You probably already know all of this.

You already have "leak proof" type seals. I always use genuine leak proof brand, classic model. Both press in retainers & the later snap ring retainers. I don't know if they make the "low friction" version in our size or not. I find the stiction of Classic to be good.

I found in testing LP Williams phenolic damper rings have basically no stiction. They have worked very well for me now in 5 bikes. Huge advantage over the rubber o-ring.

I always trial fit sliders no seals. The must move zero resistance & the clearance is a lot so they really slide freely. I recently went through fork. Found very stiff slider. Like it was dented very slightly. Couldn't polish to free it. Got new genuine Triumph NOS. It fit perfectly. Was later snap ring version. The leak proof rubber is exactly the same as the earlier slider uses with press in retainer. It MUST have the 2mm or so clearance between seal & washer under snap ring. No sealant outside of seal. It must be free to float at all times.

So now I've got 2 good sliders. Installing damper rods I could feel resistance. Inspection showed upper tip of rod was bent making piston sit crooked & rubbing on inner wall of upper tube. Took pistons off & straightened rods. Trial fitted sliders with dampers, again no seals. No slides perfectly feely both sides.

Fitting seals & damper rings both sliders now still move freely with no axle, no fender. I'd like to have spare axle to trial fit, but don't so I install wheel. Then move sliders, wheel. Adjust both triple clamps as needed to get wheel to slide freely as you can with wheel off ground so you can feel the friction. No oil in fork, but the seals sliders, dampers were well lubed on assembly. A tad of moly grease in the dust wiper lip seems to help stiction & break in of seal lip. At least fork oil. Wheel should fall swiftly when pulling it up & releasing. The goal is to reduce friction as possible. Even a little extra friction will be felt on road.

Finally the fender must fit perfectly tension free. Even an 1/8" or less bind in fender mounts will be felt on road. So after fender is installed wheel should fall like it did without fender.

Moving to springs. I know you're familiar with sag. The right spring for about 2" sag is a good starting point. Factory spring will have only slight preload from new. 1/4-3/8" above top of upper tube. Just enough to make the spring nut a little hard to start.

As we speak I have two '73 T140 type bikes in my garage. One has factory original springs. Other has progressively wound springs. Both have about 2" sag for me. I'm 163# suited & ready to ride. Progressive springs have about 1/4" less preload. 1/4"difference on these long springs is not much. On road in real life if I didn't know one were progressive I'd think springs were the same. There is different opinions about progressive wound. I have 2 friends with progressives springs on Hagon rear shocks. I'm not impressed with ride. Hate to say it, but feels same as my old originals. Maybe just me...

I always use 190cc fork oil. I've not experimented with higher. When I get old leaky forks to reseal before road test they feel much smoother, but don't always damper well as most of oil has leaked out. So in real life I've not experimented with lower oil level in controlled manner.

Regarding fork oil, I've done many miles experimenting with oils. I have a short & long road test route. Do same route to evaluate oils. The long route is 70 miles & includes every possible road surface including dirt road & very rough concrete freeway joints. I cannot overstate the effect oil weight has on these forks. Even changing oil 2.5 points of weight gives a very decided change.

I did comparisons with various ATF brands versions Shell F, Pennzoil Dexron II & III, Mercedes 134A & full synthetic. All felt basically the same. I measured oil weight with timed flow test using cups with a pin hole. Results was surprising. I still had rubber damper rings, but had leak proof seals.

For flow tests I got BelRay 10 & 5w. Compared to BelRay ATF was 7.5w. It is said fork brands set their own weight, unlike a standard like for motor oils. I don't know if true or not. I choose BelRay because friend at work races motorcycles & tunes his own forks. He feels BelRay has less stiction & helps fork last logger. So I've just used BelRay

For first road tests 70 mile long route. Being retired helps. I tried all 3 versions ATF. Very harsh on small bumps & larger bumps most of the time. Bad on freeway joints.
Next I used BelRay 10w. Was simply awful. On freeway joints 65mph actually made my eyeballs shake! On the washboard curves of the canyon roads where speeds are fairly low mostly 20-45mph as curves are sharp & some steep. A few sweepers though. One washboard sweeper I came in a little hot. Just the day before I'd used ATF 143A. I was ready for worse, but with 10w the wheel simply couldn't rebound fast enough at all. The bike was skipping sideways quickly. Only God himself kept me on the road. I was utterly shocked at how bad it cornered compared to the day before.

Next day I tried BelRay 5w. On the freeway was so much improved I couldn't believe it. On sweeper where I almost died I was very careful. No problem at all. I did sweeper several times. I could easily & safely to 5-10 mph faster than with ATF. Now I know why I had such hard time keeping up on rough roads.

Going to phenolic damper rings & still using BelRay 5w the improvement was very dramatic yet again. Gave me another 3-5 mph or more on the sweeper. The difference on freeway joints was most dramatic. Huge increase in comfort. I've covered over 1500 miles on the last set up now. You get used to it real fast. Dirt roads are so much fun & smoother.

Yesterday I took the '73 Bonnie on short fork road test. Wow. It's very nice too. Just like the other one.

On both bikes I'd pull up to stop sign & fork would stay down. If I moved at all it would come up. Now on both bikes the fork compresses when I put on brakes, then comes right up when stopped like it should. The difference in feel over old patched rural roads is very dramatically improved. I like long rides. Did 200 mile ride recently. The reduction in fatigue really surprised me. Our weekly ride is generally at least 60 miles. Last week was 90. So we actually really ride these old bikes.

If you put oil in fork before springs installed & pump fork to bleed it you can very plainly feel damper working. When I went to 5w I could already feel the bid difference. We do lots of mountain bike tuning. Except the damper ring is spring loaded on Fox Fork, the low line non adjustable steel spring fox Fork is rather similar to the T140 fork. We have done lots of tuning to our mountain bike forks. Going to the adjustable Fox forks makes it easy which I've now done. Be nice to have that on Triumph.

Back to Triumph, draining fork with drain screw & pumping a few times really does get all but a few drops of oil out.

What has your experience been in trying thinner oil in your T140? The compression damping is from the holes in damper tube. Of the ground going with thicker oil really slows compression, but on road I don't feel much difference on compression as I'd thought I would. The fork dives on braking about the same, which is a lot. I don't know what the cure for that is, if there is a cure. It doesn't bother me. My bicycle fork dives greatly, about the same actually, so maybe I'm just used to it.

Please do follow up report on what you find.

Don


1973 Tiger 750
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71 Devimead, John Hill, John Holmes A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
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For what it's worth, I've quit using the rubber seal covers and gone with gaiters. And have teflon orings on the damper rods. I noticed improvement after each of these changes.

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FWIW, heres what I have done with mine. I thought this to be a decent starting point especially when I found on my 68 A65 that by completely renewing the original damper system with progressive springs made for a real nice set of shocks over any other mod I tried in the past.

Ikon sell progressive springs, I have fitted these,

I also replaced the bottom nuts with new and bought new damper rods from SRM, I needed to anyway as the ones which came with my 71 forks for corroded.

So for me this is my starting point. As best as it can be but still factory (almost). If this is still not upto snuff then I will go the racetech route but I thought this would be a good starting point and doesnt mean im buying things I dont need anyway.


Now let’s all have a beer beerchug

68’ A65 Lightning “clubman”
71’ A65 823 Thunderbolt (undergoing restoration)
67’ D10 sportsman (undergoing restoration)
68’ D14 trials (undergoing transformation)

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There are two problems with the aluminum slider forks, the damper head and no bushes between the stanchion and slider. The original damper rod had a basic problem with the two long slots along the sides, when the stanchion bush went past the top of the slot the damper head was bypassed and serves no function. The later damper rod moved the slots down to the end and served as a hydraulic bump stop and forced all the oil through the damper head.
The damper head is a simple orifice with fixed sizes for compression and rebound. For a short tube orifice the resistance to the flow is:

Rf = dP / (Cd * A) * (rho/2)^0.5
dP - delta pressure across the orifice
Cd - orifice coefficient
A - orifice area
rho - fluid density

As the forks move faster the resistance continues to increase.
Reed valve damper heads are non-linear and the resistance decreases as the reed opens further due the the pressure. By changing the dimensions and number of the reeds the damping characteristics can easily be tailored.
For very high impacts a blow-off valve is used, typically a spring against the reed stack.
This is one way to change the damper head to reed valve.
[Linked Image from live.staticflickr.com]
The screw allows overall damper adjustment and the reed valves add a non-linear portion.

The sliders are not hard coated and have no bushes. When the stanchions are bent the slider is straightening the tube as it moves up. The majority of the load is concentrated at the end of the bore. Modern forks have a bush at the top of the slider and another on the end of the stanchion that allows the stanchion to flex in between. Some stiction can be reduced by boring the top of the slider bore and putting in a bronze bush. Another is to replace the slider with a hard anodized one made for a bushed stanchion.
[Linked Image from live.staticflickr.com]

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Thanks to all who have posted so far, there is a lot of information here. I was wrong about oil height— I set it at 140mm, not 125. That moderates the air spring effect somewhat. Anyway, keep it coming, this is a great trove of ideas.

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Install an emulator kit.
https://www.racetech.com/ProductSearch/12/Triumph/T140%20T140V%20T140E%20TR7%20Bonneville/1978

Sorry should have read more...but TL:DR, my attention span timed out.

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I looked at the Race Tech valves. The difference from the original damper head, besides the reed valves, is the direction of the flow through the valve is opposite. The original damper under compression has the oil pushed into the inside of the damper rod by the stanchion, the oil goes up and out the top nut into the spring space then down through the damper head into the space between the damper tube and stanchion.
The Race Tach has the flow go up through damper tube and through the new damper head into the spring space. The original damper head is just a seal holder against the inside of the stanchion to keep the oil from bypassing the new damper head.

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Whist there are improvements like the race tech, the original fork setup with a twin I find to be quite good providing everything is in good condition. Hence why I suggested easy to change mods first. Like the progressive springs and renewing the damper rods. This can make a big difference to the performance alone, just by replacing the parts that wear.


Now let’s all have a beer beerchug

68’ A65 Lightning “clubman”
71’ A65 823 Thunderbolt (undergoing restoration)
67’ D10 sportsman (undergoing restoration)
68’ D14 trials (undergoing transformation)

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I actually had my fork leg 'throats' reemed out and a phospur bronze bush pressed in then turned to size. One of the legs had a bad scour in the area just below the seal, this fixed it. Plus I always hated hard chrome on aluminium, this fixed that as well. Ended up doing it for both twin and triple.

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Looking at the worn forks on my T140 D a few years ago...Worn fork tubes, the left hand tube was bent back slightly...I was told this is from the braking force, hmmm. The springs were sacked so should be replaced. It seems many replacement forks are not smooth inside ..How is the damper o ring supposed to seal on a rough surface?
The price of a quality set of stanchions, new springs and an improved dampening system is crowding $500..
As Allan says, a replacement of worn parts should becadequate for most riders...Unless like me you find impressive improvements from a fork swap...


79 T140D, 96 900M Ducati ,61 A10 .On a bike you can out run the demons.."I don't know what the world may need
But a V8 engine is a good start for me
Think I'll drive to find a place, to be surly"
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Originally Posted by Hillbilly bike
As Allan says, a replacement of worn parts should becadequate for most riders...Unless like me you find impressive improvements from a fork swap...

I think when your pacing at over 120mph (like the LSR) you need that something extra.


Now let’s all have a beer beerchug

68’ A65 Lightning “clubman”
71’ A65 823 Thunderbolt (undergoing restoration)
67’ D10 sportsman (undergoing restoration)
68’ D14 trials (undergoing transformation)

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Originally Posted by Allan G
Originally Posted by Hillbilly bike
As Allan says, a replacement of worn parts should be adequate for most riders...Unless like me you find impressive improvements from a fork swap...

I think when your pacing at over 120mph (like the LSR) you need that something extra.
My LSR bike has non rebuilt OIF T120 forks, the track is smooth, lol...The roads around here are mostly bumpy and rough so anything to improve fork response is good...


79 T140D, 96 900M Ducati ,61 A10 .On a bike you can out run the demons.."I don't know what the world may need
But a V8 engine is a good start for me
Think I'll drive to find a place, to be surly"
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My T120 forks work better than my T140 forks, too.

I certainly understand the attraction of modern forks, it's just that I want to stay with the stock forks and get them working as well as I can. (And realistically, this is a vintage bike, and I sort of expect it not to have great suspension, but this seems like it can be improved).

I have tried Race Tech Emulators on a race bike, and they worked fine, they are a good product, but I wanted to try other alternatives first. The problem, if there is one, with Race Tech is, they pretty much add their compression damping system to the rest of the stock fork, for instance they use the rebound damping that is stock in the fork, and might also continue to suffer from the stiction problems inherent of the stock Triumph forks--which is what I am trying to fix first. Maybe after I solve that, if possible, I'll try the Emulators?

I had an AHRMA F500 Yamaha road racer with 38mm Yama FZR600 forks on it, and I tried Emulators in it first, but like a lot of bikes, the FZR 600 forks have waisted damping rods (to free up the middle of the travel) but that caused a problem because that also took away rebound damping in the middle of the travel as well, and as a result I could not get rid of a persistent chatter. To solve that I eventually replaced the stock fork innards and Race Tech Emulators and with some Honda CBR600 F3 or F4 cartridges, and problem solved--they worked really well. I am thinking of maybe doing that here (if they will fit) but really, I just want to get the more or less stock forks working as well as I can first, before I do anything that ambitious.

And my Sportsman 750 Triumph in a Champion frame had Marzocchi 38mm forks, with a custom set of cartridges that my buddy Gil Vaillancourt at Works Performance made for me as a sort of prototype, and they worked really well too. So I may end up with either Emulators, or cartridges, but first I need to get the darned stiction and such fixed.

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Hi linker48x, Ok, you know what you're doing obviously. Your forks should have leak proof seals already from factory. You have phenolic damper rings. Boot would give less stiction than dust wiper, but I find dust wiper moves pretty easily.

So that only leaves oil. 5w in my experience in 5 T140 forks is a huge improvement. I always use Belray 5w. But give it a try & see what you think. The 5w substantially helped the sharp small bumps you speak of. Greatly improves handling on bumpy curves. Give it a try.
Don


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Thanks for all the comments, guys. A couple things I did not mention: first, my 1979 T140D does not have leak proof type seals, they are just the ordinary double lip seals, and I replaced them a couple years ago when I built the bike. These forks have no circlip grooves for the leak proof type seal. On the chance that these are the problem, I have just ordered a pair of the Leak Proof seals Promoly pn# 5216 https://leakproofforkseals.com/Leakproof7216.htm , and I bought on Ebay a pair of the 97-7016 thick press in steel washers for the top to hold them in. I haven't used Leak Proof seals since the 70's or early 80's, and my experience then was not good, but I will give the brand another try to minimize the stiction.

I also replaced the wipers some time ago, and I am wondering if these might fit too tightly. I did lube them, as always, with a bit of light moly grease and some fork oil when I just put the fork back together, and will again, since I am taking it apart again. I also do a bunch of mountain biking and using MB fork grease is a good idea.

A couple years ago I also replaced the stock worn fork tubes with a pair of repop fork tubes. I understand these may have a rougher finish inside (I am hoping the piston rings fix that) that doesn't work well with the o-rings, and I have heard their dimensions might vary slightly from stock. Using a micrometer, the old fork tubes measured 1.360, or 34.54mm and the replacements measure 1.362, or 34.59mm. The repop fork tubes thus are .002 inch greater in diameter. I don't have the sliders off so I cannot measure their i.d. but sliders are usually pretty loose on the fork tubes, and I cannot imagine that a deviation of only .002 is affecting the stiction, although I am curious what others think on this.

I did already make the fender fit the fork, when I first built this bike several years ago. It was way off, an obvious problem. TR7RVman, you offer a lot of practical advice and make a good call on this, mine required compressing the fender bracket by maybe 2.5 inches to get it into the mounting lugs before I fixed it.

On the subject of fork oil, measured viscosity can deviate widely from the number on the bottle so much that it is definitely worth paying attention to. If you google "Fork Oil Viscosity Chart" you will find a number of charts that measure viscosity in centistokes at various temps--the 40 degree C seems the most relevant. Here are a couple examples of such a chart. http://mahonkin.com/~milktree/motorcycle/fork-oil.html and http://www.peterverdone.com/wiki/index.php?title=Suspension_Fluid You can see that the Bel-Ray 5 wt is right in there with a lot of other comparable brands of 5 wt premium fork oil. You also find strange things, like, the Castrol 10 wt is lighter than the Motorex 2.5 wt., and while it is not on the list, I have used Harley 15 wt and it was too light to work in the forks I put it in, like circa 5 wt. And if you cannot find the stuff you want at a local dealer, I've had no problem ordering quality fork oil over the internet if I cannot find what I want locally. Try your favorite brand on Amazon, or any of the dirt bike mail order houses.

Thanks for everyone's comments to date, and I will be looking for more comments from y'all.

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Hi, I’ve always used the leak proof classic. I don’t know how leakage compares to promoly.

The leak proof package states min float is .020” (.5mm), 2-4 mm float is no problem. Snap ring retainer is not adjustable per se. The ones I installed recently had .7mm float. Sealing perfectly so far.


If you look close there is small chamfer on top of slider where seal goes. I press thick retainer in until top of retainer is just flush with bottom of chamfer. This gives good float. Again I use leakproof retainers. Aftermarket may differ.
Look at RAT site. I posted photos there the other day. “Fork”.

Pm your email. me & I can email you photos.

I find leak proof classic has 1/8-1/4 the stiction of normal seal.

I ride mountain bikes too. Stump Jumper FSR. Old now but still riding it. Fox spring fork in front air in rear. Resealed both a few times already. Adjusting/tuning bicycle forks transfers to motorcycles. Bicycles much more sensitive. You can really feel compression & rebound adjustments. Both my ends are adjustable. I think about this stuff while riding either all the time.

Sometimes I find rust or rough ID of upper. I take wood dowel, cut slot in end & stick emery paper in it. Put dowel in electric drill. Use solvent for cutting fluid.

Now things are adding on your fork. That’s why I always say Belray. I would try the 5w. I always use 190cc.
Different will change air spring effect. I’ve never used more. Not much less & you start loosing damping.

Some measure oil level. You’d do that if you start messing with air spring effect Since 190cc works good for me I haven’t experimented with that. 190cc is for stock tube length. Check Manual spec of course.

Peg (rancidpegwoman) on RAT has. She is very smart, skilled & experienced.

Looking like rain tomorrow. I’ll try to ride the last reseal on long road test Sunday. I got Modera covid vaccine Thursday. Kind of threw me for a loop. Very fatigued & just felt odd. Better today so I got some work done.
Don

Last edited by TR7RVMan; 02/13/21 8:15 am. Reason: Changed sentence

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Have you tried the TQF from Castrol as recommended in the Manual?


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The problem with both the 2 way damper valves and the shuttle valves is that between the compression mode and rebound mode the valve/shuttle has to move. During this movement there is no damping as the oil is moving the valve and not going through the valve. This gives you virtually no damping on smooth roads with small fork movements, this is the exact time you want the highest damping. Without going for a full modern setup the easiest way to improve these forks is to break the compression and rebound and dedicate one leg to compression and one to rebound with a fast acting release valve to give no damping in the reverse direction.

As for the Racetech valves as noted for rebound damping they rely on the current rebound system in the leg. This works on later Japanese rod damper forks but on British rod damper and shuttle valve when you install the Racetech valve you have to remove both the compression and rebound systems. So you end up with compression damping only unless you can reengineer rebound damping possibly by replicating the Japanese rebound damping system.

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Not taking away anything from the race tech units or anything like that. I have noticed that a lot of beakers /jugs etc where your measuring the volume of oil from actually measured a lot less than the beaker states. Part of my job is pipetting precise volumes, we have some Scott glass beakers which I can pour 100ml of sample in yet when I draw the sample up into a calibrated pipette it actually comes no where near. This is supposed to be fairly accurate glass wear.

I’ve found on my pre oif by measuring out the actual volume required I get a much nicer ride. You can also do this by weight if you find the density of the oil your using. (Density changes with temperature but it’s usually reported at 15°c - but not always and the difference will be not much more than +/-1g)

The TQF I’m using has a density of 0.865 kg/l multiply that by the 190ml of oil I need to use and you get a weight of around 165g.

Again something you can do before you spend a penny on other parts. I find standard forks on an oif to handle quite well.


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On the original damper head the oil flows down through the head on compression and up in rebound. The floating restriction washer is on the bottom side so yes, when the travel reverses direction the restriction is still on the compression holes until the washer moves up. However, the compression side of the damper is negligible with ATF or light fork oils.
On the damper head that I made, the compression reeds are on one side and rebound are on the other so there is no transition period without damping.
Making one leg the compression damper and the other rebound will put a bending moment on the axle. Modern forks can handle this load but these 34.6mm forks are much less stout than used on modern USD and will cause the wheel to tilt sideways.
The best way to measure fork oil is not by volume but over filling and using a suction tube, draw out the excess to a measured level. That accounts for any variation in tolerances.

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Originally Posted by DMadigan
The best way to measure fork oil is not by volume but over filling and using a suction tube, draw out the excess to a measured level. That accounts for any variation in tolerances.

What are you using as your datum?


Just done by weight on my oif, on the measuring jug I use it measured out at 200ml. Fairly accurate for a plastic jug. Poured the oil in and weighed the excess, in my case it was 3grams. Added that value again and poured the excess and weighed again and once again got 3 grams, the other leg was 4 grams remaining after pouring. Zero’d between doing each leg.


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You could start with the 190cc and find the depth of that, check the same amount in the other leg measures the same height. The amount of oil does not change the damping unless too much is sprayed up on the springs and the damper head sucks air.. Oil level changes the air spring stiffness.
I believe it was the first OIF damper nuts had lateral holes in the top and later had vertical hole.

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