Forks (2007)

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Ifyou do fit the Covenant kit ensure that "floating bush" doesn't float. It should be fixed below the slider bush to cover the holes in the stanchion at full extension to provide the hydraulic stop. If the bush is allowed to move the fork action becomes stiff and erratic.
Cash

Correct. I am very sorry if RGM, to whom I sold a few kits with accurate instructions, have not only pinched my idea and spoiled it but rendered it unsafe IMO. The folks who have no trouble with a floating sleeve can probably thank iffy slider QC and uneven wear for the fact their ‘floating’ sleeves are probably stable and stuck at the top.

Remember that the sleeve and dowel kit was only made available for readers of the seminal article in British Bike Magazine who were “...ready, willing but unable...” to follow the instruction to make bespoke longer top bushes or trim the collar off existing old bushes and glue them in place under the top bush.

I live in the States now and as soon as I finish my D-Type Jag will blow the cobwebs off the Covenant Commando (312 lbs with oil/no fuel) and sell it for my grandchildren. Will keep an eye on this forum and answer questions within reason, or you can PM me and try your luck that way: pcrespin at jcna dot com.

Pete
 
cash said:
If you do fit the Covenant kit ensure that "floating bush" doesn't float. It should be fixed below the slider bush to cover the holes in the stanchion at full extension to provide the hydraulic stop. If the bush is allowed to move the fork action becomes stiff and erratic.
Cash


The answer to the unwanted "floating sleeve" is a slit and expanded sleeve - as I have been offering. Its a hand press fit and it stays at the top where its supposed to stay.

Forks (2007)


The two set screws are for plugging the small holes in the steel fork tubes otherwise you can still have top out "clunk" on a bumpy road.
 
A question for Peter then...What part of the RGM conversion is potentially unsafe?
I have this afternoon rebuilt my forks and they have the RGM version of your modification. RGM instructions do say that the sleeves should be secured with locktite and although mine did come apart it was a bit of a slog because of being over generous with the locktite. I have now flared the sleeves and slotted them per the JSM examples.
The concern I have with the RGM kit is the aluminium rod that is pushed through the base of the damper tube to block the original holes. This rod now obstructs the damper assembly a short distance above its normal bottom. In use the bike has never bottomed out and there are no impact marks on the rod that I can see so I have left them as they were.
 
RGM instructions do say that the sleeves should be secured with locktite

The RGM instructions do now, but they didn't (as this thread is from 2007).

These are the instructions that came with my Covenant kit Edit: purchased sometime before 2007 (removed some years ago and replaced with Lansdowne dampers and RGM extended upper bushes).

"..........The alloy sleeve sits on the fork stanchion below the top bush. Basically being free to float."

Forks (2007)


The concern I have with the RGM kit is the aluminium rod that is pushed through the base of the damper tube to block the original holes. This rod now obstructs the damper assembly a short distance above its normal bottom.

Plugging the damper tube and drilling the hole(s) higher up does precisely nothing as far as I can tell and this has been misunderstood by RGM.
With the fork fully comressed the damper rod/piston is still some distance away from the dowel and doesn't even reach the upper hole.

Forks (2007)


Forks (2007)
 
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A question for Peter then...What part of the RGM conversion is potentially unsafe?
If you have a kit with top sleeves designed to stay in place then you're OK. I understood there was a kit and modified instructions referring to a floating sleeve, which I would expect to cause unequal and unpredictable damping. I've never seen one myself, but reading here it seems there is such kit or instruction sheet?

Splitting the sleeve could be fractionally sub-optimal if the split aligns with a hole, but in practice I'm sure it works. I just don't see an advantage over a dab of any old goo like silicone or Loctite to hold the plain sleeves in place. The Triumph sleeves I referred to in the article are some kind of nylon or Tufnol and are longer, with externally-butted close-fitting end sections that are a snug fit and stop it being pulled down the slider on compression.

I'm not sure I follow the dowel issue at full compression. There is some guy on a YouTube video who nicely blocks off the bottom holes and then drills new ones halfway up the taper - doh! He thereby swaps a bad problem for a needless if less bad problem, instead of drilling just above the taper and curing it. What is the point of having a taper restriction and nullifying the effect by drilling holes in it ???? That's what Norton's 'improvement' was. I know Norton ended up buying AMC and therefore you'd think they got the rights to the Matchless Teledraulic patents. On reflection, maybe there was still some restriction on Norton's use of the design. My old off-road G80 was a heap but the Teledraulics never clanged when green laning. I can't think why Norton would deliberately sabotage a working design to sell forks with non-functioning stops, unless they had to change stuff to avoid patent infringement.

My kits weren't worth a patent but I did do dated/signed drawings before going public. I stopped making the kit after a year or so as my work as a medical writer got busy. When I found out years later that RGM were still selling them, even using the name, I got a friend to order a kit incognito to be sure it was the same thing. When I saw it was I wrote to RGM gently complaining at my loss and asking for some Norton spares as compensation so we could settle up and it would be theirs to do what they wanted. I never heard back and I guess that's when they started offering longer bushes, which is the correct fix id done properly. It's scary to think some people use longer damper rods, leaving a 400-odd lb bike supported by only an inch or two of slider overlap at full extension.
 
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I understood there was a kit and modified instructions referring to a floating sleeve, which I would expect to cause unequal and unpredictable damping. I've never seen one myself, but reading here it seems there is such kit or instruction sheet?

= Was. Well, I didn't experience any unequal or unpredictable damping.


I'm not sure I follow the dowel issue at full compression. There is some guy on a YouTube video who nicely blocks off the bottom holes and then drills new ones halfway up the taper - doh! He thereby swaps a bad problem for a needless if less bad problem, instead of drilling just above the taper and curing it. What is the point of having a taper restriction and nullifying the effect by drilling holes in it ????

As I understand it, there's nothing to be gained by drilling holes any higher than the mid-taper position.

http://atlanticgreen.com/forks.htm
Analysis.
 
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Yes the holes do not need to be higher than the mid taper section. But if there are holes below the taper (early style) then they need to be plugged and a new hole (1/16" dia is best) drilled at mid taper or higher - because it is the oil OUTSIDE the damper tube that gives you a hydraulic bump stop (not the oil inside the damper tube) as shown in the orange and white illustration above.

Using silicone or loctite on the sleeves means you will have to force them out to disassemble your forks and if you use loctite you are going to have a problem. You might still have somewhat of a problem with silicone (and who wants that debris in your fork oil).

As for the slit in the expanded sleeves, its easy to locate the slit away from the damper holes. Here are the instructions:

"Place the slit in the aluminum slider so it is located opposite the large hole near the bottom of the steel fork tube. When assembling the forks you will have to pinch the upper sleeve slightly to get it started into the aluminum fork slider."

For details about fork dampening improvements and photos showing the 1/16" hole for slight compression dampening (instead of 1/4") go to this page:

https://jsmotorsport.com/js-motorsport-technicalmore-norton-fork-upgrades/

Do all these things and your forks might just enter the modern age.
 
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Gentlemen,
Thankyou all for your explanations and comments. I think that I am most happy that the forks presently lying all shiney on the bench ready for refitting do not have to be disassembled even though they have holes in places that are no more effective than the ones that I plugged. And many thanks also for the generosity of all of you for publishing pictures and drawings that show how things should be.
 
= Was. Well, I didn't experience any unequal or unpre dictable damping.

Good but some did, apparently, according to what some have posted who had floating sleeves. The whole sleeve idea was a second best option for those who couldn’t get longer top bushes made TO A CUSTOM LENGTH checked to suit their damper tube, damper rod and other measures so the shuttle valve stays just clear of the damper top at the new minimally reduced full extension. I thought about doing some long bushes originally instead of sleeves but the three new stanchions I tried were sufficiently inconsistent that one size didn’t fit all correctly so I knew I’d be in trouble with complaints. My own ones in PTFE I think were slightly different ID. The OD was easier because the flange holds them.

I saw the analysis too but had two slight issues with it:

It was unrealistically precise IMO, in that accuracy to several decimal points seemed a bit odd for parts accurate and consistent to maybe two? They are not precision parts like crank journals, especially taper max OD after a few decades and stanchion ID which looked just rough turned on mine

More fundamentally, and nobody has answered these points from the 1987 article:

1: my original damper tubes were drilled on the taper flanks and the Teledraulics weren’t.
2: The Roadholders clonked at full bump and the Matchless didn’t.
3: Crucially, by filling the holes and re-drilling as per Matchless, the bump stop on my forks worked. So even if we all agree the easy win is to block holes below the taper, there is additional benefit available by redrilling just above the taper and nobody has suggested any downside. So why go to the trouble and then skip some of the benefit from the original ‘pure’ Matchless design by deliberately putting holes in the restriction. Seems an odd thing to do?

If we have open minds and the ‘null hypothesis’ is that above the taper is no better than halfway down, then someone has to explain results/data points to the contrary, achieved with a single changed variable. That new hypothesis then gets tested and a new analysis done and so science advances. Scepticism is the engine of advancement but we do need to process all data, not cherry pick.

Still, who gives a damn? This only came up because I saw a kit for sale on eBay the other day. If email and the internet had been around in 1986-87 I’d be rich enough to buy brand name toilet paper LOL
 
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Hello JS

Nice website but a few queries.

There is, of course, some compression damping just by components moving in oil.

1) Oil passes into the expanding annular gap between the top and bottom bushes through the stanchion holes.
2) oil flows past the damper piston and through the open damper valve as the forks compress. Doesn’t matter if the stanchions are going down or the sliders go up, there’s still resistance.
3) oil flows through the comparatively large space between the outside of the damper tube and the inside of the bottom bush.
4) There’s our old enemy friction, but except on girders we can choose to disregard that here

This is certainly less damping than on rebound, which is typical of suspension, when the damper valve closes and your neat brass sleeve restores maximum effect, but it definitely can’t be dismiised as ‘no damping’. Remember that the long Roadholders - which won high praise and lots of TTs at the time - had no damper tube or valves at all, just the damping described above in points 1&3. As I wrote 32 years ago, the double opposed restrictor system worked well for the time and the top & bottom bump stops were intact. It was just the mid-travel section, where the restrictor was a simple cylinder, that was worth improving, which the damper tube design did. It just messed up the bump stops.

By blocking the holes and drilling a single 1/16” hole you certainly beef up compression but that doesn’t mean there was none. It also means you need to be careful not to overdo it not just on compression but because oil also has to pass into the damper tube on rebound.

I’m not surel what you were saying about the oil on the outside of the damper tube forming the bump stop. Everybody has presumably figured that out on day one. I expect oil flows both ways through the damper tube holes at various times but no oil is truly captive as a bumpstop until it has been trapped in a blind space where there are no holes.

The standard rod and damper valve never go as low in the tube as to pass any holes, so you can blank off the taper holes and drill in the Matchless original position and ignore damper position.

On a related note, if your split sleeve doesn’t cover the small hole why make it so short that you need to use a tap and screws? There is a blind section of stanchion at the bottom between the bush and small hole that works fine as a bump stop. More doesn’t mean ‘better’ because oil is incompressible so 10 cm3 is no better than 5 mL for a transient static purpose like preventing metal to metal contact. Still, if I had my time again I might have made my alloy damper tubes with 2 x 3mm holes instead of 2 x 6mm and lined the tops with brass. You can always drill bigger holes quicker than shrink them :)
 
Peter

For the most part you have explained what goes on in Norton forks. But the compression dampening you mention is not adequate the way Nortons are originally set up. More than one hole bigger than 1/16" in the tapered portion doesn't give any meaningful compression dampening. Smaller than 1/16" can create a vacuum inside the damper tube during extension - when & where you don't want it.

And the short blank space you mention between the lower bush and the 1/8" hole in the steel fork tube is not enough to prevent topping out clunking on a bumpy road even with the sleeves installed - you need to plug the 1/8" holes or you're going to have clunking when you hit a repeating series of bumps.

It takes actual testing, experimenting, more testing and refining to work this stuff out. You can't just analyze it. When you think you've got the solution and then go out and test it - you usually learn something has fallen short and so you have find another solution - over and over again until you get it right.

If you want to test your theories the best way to do it is to bench test with a container of fork oil and your damper tube. Also bench test with oil in one fork assembly but with the damper rods removed. That's what worked for me.

The atlantic green article says "The reasons the factory manufactured the forks this way may hopefully be made known to us all one day." The real reason is because someone seriously botched the Norton damper design at the top out and bottom out ends.

I'm not sure if the Landsdown dampers has solved this topping and bottoming problem either (other than cranking up the entire dampening range) - does anyone know for sure?
 
I dunno. I'm old fashioned perhaps. There are people calling me by my name, which is fine, but I've no idea who I'm talking to. Feels weird. Never mind. Can I call you John?

You are arguing against yourself slightly. As a scientist I totally agree with the need to measure, remeasure, modify, test etc. Objective data points rule. But you make a subjective value judgement about the compression damping not being adequate. Inadequate for what? Judged by whom? Under what conditions and for what purpose? Without those basic qualifiers you can't sustain your view as being superior to anyone elses, which is fine if we're just joshing but not if we're claiming technical precision.

I can pretty much guarantee that Mick Grant or Peter Williams on an old heap with no fork oil and worn isolastics could blow us off on race-fettled machinery, so in what sense were those old nails inadequate? I never really had a compresssion problem, but then as you can see from the bike photos I also made linked air assistance and variable damping for my Roadholders too, plus somewhat of a fork brace. Not too shabby for a total autodidact who didn't even do woodwork, let alone metalwork at school. Frankly, it would take me some time to get back to the screw cutting etc I did back then.

I even took my home made belt drive to Mick Hemmings to ask about tooth cutting for the then-new HTD belts - the only UK location with a licened tooth cutter was in Scotland IIRC. A few months later, guess what, Mick starts selling belt drives just the same as the one I showed him and then everyone was doing it :) A few years later I beat him in the MCC high speed trials at Silverstone in the pissing rain and was first British bike home, but honestly there weren't many entered and Mick would have beaten me if his crank cases hadn't been inadequate. That's NOT a value judgement, because there was about half an inch of fresh air where the barrel should have been (all subject to dodgy memory).:)

Same with your statement about the thin ring of oil being inadequate to prevent topping out. It did on mine and did on a Le Mans car racing friend's Commando that I rebuilt for him. 2 out of two that I did, but still only a small sample of course.You and I would have fun in a workshop. We would need to find where was it topping out - the damper valve as original, or some mismatch in parts dimensions somewhere. Did you read the article where it says how I discovered this, by wheeling my engineless (therefore massively over-sprung) alloy chassis around and noticing the clanking? I did the work, measured everything and got the ring of oil working and no metal clank. QED. I dry assembled fork legs, wet assembled them, with/without springs. Norton, matchless and Triumph. There. Was. No. Clanking on short Roadholders with the small hole left open, as long as there is oil and the sleeve/bush overlaps the holes on full extension. I think your split sleeve idea is neat if installed right, but one finger dab of silicone or drop of blue non-hardening Loctite is not exactly hard to reverse for dismantling. YMMV etc.

Remember that I was a 33 year-old medical information specialist and total amateur engineer. Can you imaging how vulnerable I felt publishing a paper critical of a design that in those days was regarded as the finest Brit fork, sought-after and boasted of by owners in the small ads. Who the heck was I to take them down? Nowadays everyon can say they are flawed and nobody bats an eyelid.
 
I saw the analysis too but had two slight issues with it:

It was unrealistically precise IMO

You'd have to take that up with the author but I can't see how it's much of an issue as it says they are mathematical figures.


More fundamentally, and nobody has answered these points from the 1987 article:

1: my original damper tubes were drilled on the taper flanks and the Teledraulics weren’t.
2: The Roadholders clonked at full bump and the Matchless didn’t.
3: Crucially, by filling the holes and re-drilling as per Matchless, the bump stop on my forks worked.


Prior to doing the 'Covenant conversion' to my Commando's forks, I don't recall there being any clonk or harshness at full compression or any noticeble difference or improvement afterwards, it was simply part of the Covenant modification that supposedly "improved damping" according to RGM's literature.



One interesting point, in section 5, p15 of my RGM's 'Special Products Brochure Number 2' in their description of Covenant conversion it states....:

"The aluminium dowels are used to block the bleed hole in the bottom of the fork damper bodies. These holes are then placed further up the body. The effect being that as the piston on the damper rod passes the bleed hole a hydraulic lock is achieved below the bleed hole and this prevents the fork from bottoming out."

...which of course is completely wrong as the damper piston never passes or even reaches the level of the raised bleed hole.



So even if we all agree the easy win is to block holes below the taper, there is additional benefit available by redrilling just above the taper and nobody has suggested any downside. So why go to the trouble and then skip some of the benefit from the original ‘pure’ Matchless design by deliberately putting holes in the restriction. Seems an odd thing to do?


I think perhaps we can agree that blanking off the (4) holes below the taper in the early damper tube design would improve the compression buffer which makes me question why the modification for the early damper tubes wasn't available as part of the 'Covenant' conversion? I have no experience of Matchless forks so can't comment on any working differences when compared to Roadholders but since doing the dowel modification I personally didn't notice any "additional benefit".



I'm not sure if the Landsdown dampers has solved this topping and bottoming problem

Early Lansdownes did not have an extension buffer but the later versions do. Edit: (All have a compression buffer as far as I know)
 
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We an certainly agree that story thing by RGM is wrong and in direct contradiction of what I wrote. I haven’t seen anything from them for thirty-odd years except the sample kit a few years ago.


So for the 4 said dampers I referred to using a sleeve, epoxy or welding gear in the article I think. One full dowel and two short stumps would do it and four half dowels would do it. My kits had 4 dowels, two sleeves anf illustrated instructions in English, French, Dutch and German (I’m from a Belgian family) .

I think most people hardly ever feel true full bump so it’s not surprising the road testers at the time didn’t complain. I checked by using one spring and jamming the front wheel against a wall (I’m pretty big). I also worked an open no-spring leg by hand with and without some oil and the compression bit was fixed.

The extension clang is more common but some riders on smooth roads may rarely get caught out by it , I guess?

Bottom line, They were ten quid of cheap fun and it’s not like I was claiming anything about damping or handling, justvbump stops
 
Yes, but then, the extension clunk is no more than a minor annoyance.
On a 300lb lightweight with taut/stiff cast alloy beam frame, and with your face over the forks, it is more prominent than on a heavier softer sit-up stock bike. Plus since I was making new internals to save precious ounces, there was no way I was going to copy the faults.

The vibration from a rigidly-mounted Dunstall engine is an annoyance I have no choice but to put up with, but if it's fixable it gets fixed.
 
On a 300lb lightweight with taut/stiff cast alloy beam frame, and with your face over the forks, it is more prominent than on a heavier softer sit-up stock bike. Plus since I was making new internals to save precious ounces, there was no way I was going to copy the faults.

The vibration from a rigidly-mounted Dunstall engine is an annoyance I have no choice but to put up with, but if it's fixable it gets fixed.

You do have a choice and you can have a much smoother rigidly mounted Dunstall engine. Many others are enjoying reduced vibration now with rigidly mounted Norton motors - including myself. Yes you can fix it. PM me for details.
 
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You do have a choice and you can have a much smoother rigidly mounted Dunstall engine. Many others are enjoying reduced vibration now with rigidly mounted Norton motors - including myself. Yes you can fix it. PM me for details.
Ba
 
I agree improvements are possible. What I meant was it’s a historic motor and I don’t want to alter it. The vibes were OK to me after a life of Triumphs! It could do with Cooper rings at the head joint. Motor hasn’t run in twenty years as the new K2F mag gooed up m. Is there a self generating magneto shaped electronic ignition anywhere? Not alternator based or rechargeable race setup.
 
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