FF: Forks Koni damper modification

[oexing]

Triggered by the never ending story about the Vincent standard damper I got curious about the report of very stiff Konis. So I looked inside two NOS adjustable type Konis I got from the Spares Co 30 years ago - and was not impressed by the seals inside. The dust wiper seals were allright but the hydraulic seals were just punched out rubber material, compressed by the top ring nut for sealing the contents. So no surprise that the damper had a tough feel way too stiff from that type of "seal" . So instead went for real polyurethane hydraulic u-cup seals , no question about o-rings for rod seals certainly.
Konis are wellknown for stiff compression forces, extension setting is easy to dial with the classic bottom key for preloading the extension valve from light to very strong. No big deal but the compression setting had to be worked on , basically set by a stainless spring steel wave washer acting on the extension valve. I took the washer out for testing with 1 mm gap in the set but this gets you a few mm of backlash so in again but I hammered the wave washer for a lot less preload on extension valve. For oil fill I used HLP 10 hydraulic oil as you don´t want oil foam forming in hydraulics, would be cathastrophic in hydraulic machinery. You fill up oil till no backlash in full stroke from air is noticable and then a bit more. There will be some volume of air certainly but not critical here in standard mounting condition on the bike. Same with the original damper, some air inside is required .
So my conclusion, once you changed these rubber seals for real u-cup types by fabricating an alu adapter bush to go in the big ring nut and another wiper seal in the brass top nut you just do a bit of hammering the wave washer to your liking and the Koni should do nicely on your Vincent for decades.
In my eyes the main flaw of the original Vincent damper are the o-ring seals acting on some soft steel piston rods - no durable combination. We had endless measurements here of components to four figures but no hardness numbers of the rod. Not surprising the leaking calamity then, you will not find any shock absorbers or teleforks since mid-fifties with non-hardchromed piston rods or stanchions - not for good looks or rustprevention, but for protection from scoring, like with hydraulic machinery with their cylinders. So simple action on the original damper: Get u-cup seals and have the rod hardchromed or copy it from cheap hardchromed piston rod material. But yes, you still have the same damping for compression and extension, Vincents were still stuck in their friction damper thinking at their time - not my choice .

Vic

old Koni seals:

wave washer left, fat spring for extension preload:

u-cup seal in alu bush, blue dust wiper in brass top nut :

assembled Koni top, below a Hagon piston:

 

[greg brillus]

Interesting findings there Vic, I have a big interest in suspension, especially on these bikes........I have done tests using my bike and changing the front shock absorber as many as 5 times in one afternoon of testing. This might include, a factory original shock, a Koni, both versions of the Thornton's, an Armstrong, and even my own modern nitrogen filled pit bike shock that did work, but it was too stiff in it's action.....even after I deliberately dumped the nitrogen out of the unit to ease up on the compression damping........Of course this is using the highly recommended modified steering stem, and 45 Lb springs up front. It is very important on these bikes to ensure that the friction caused by many items on these forks is reduced as much as possible to make the fork action as smooth as possible....... I can say with most confidence that a good percentage of bikes out there have forks with too much friction.......even the smallest of drag from the spring cases will slow the fork action........this with stock springs which are too strong, and a strong damper all make for a front end that is not good at all. I have had many discussions with Ikon, the continuation of the Koni's, that oddly are based here in Australia........the new shocks they supply are very well made verses their earlier ones that were not the best in my opinion........They list the new shocks as being the same front and rear.......I have told them (politely) that this is simply not the case........A new one on the front is way too stiff in its action.......I sent 2 new ones back to them to be re-valved much softer on the compression and rebound........These returned after about 4 weeks ( they are very busy) the re-valved item felt better when tested with hand pressure in the vice, but still too stiff on the road........so sent back again to soften the rebound some more.......It will be interesting to see how they come up........If successful I will order a small batch of them made to my specs........they are not expensive, so well worth experimenting with.

 

[bmetcalf]

Is this the item you work with?

https://www.ikonsuspension.com.au/?make=1751&model=1752&year_id=&post_type=product&action=vpf-search

 

[Chris Launders]

I have to agree with what Greg is saying, but you must use the modified steering stem to use the better suspension safely, when I initially fitted the stem with the standard springing and a Koni damper I was getting 1" to 1-1/4" of movement on the front spring boxes in everyday use, this included speed bumps and potholes so basically unless the road was rough the forks were solid. Like Greg I went through many damper changes in quick succession trying to improve the situation, I have ended up with needle rollers in the bottom link 45lb springs and a Avo damper on the lowest setting and now have 2-1/2" on the spring boxes in everyday use but cannot bottom it out and the forks are really active, moving constantly with even the slightest irregularity.

 

[greg brillus]

To answer Bruce's question , yes they are the ones........I'm guessing that price is for 2 of, they are much better than the earlier ones whereby the upper attachment had a vertical blade of steel that was welded on and not very nice, not to mention crooked. They are not adjustable like the original Koni's, though even on the weakest setting they are too stiff........perhaps Vic's findings of the primitive punched out seal is partially to blame. You need to remember that most folk who ride the "B"s with Brampton's say how nice they ride, and I would agree, save the limited travel which readily shows itself on rough roads........However, the forks do move smoothly and as we know the damping is very basic........ So with that in mind, the later forks are not that different. Their relative unsprung weight is not much if at all different....... There are many things about these forks that do not at first come to mind........The pivot point for the lower attachment does not move at the same rate as the fork blades themselves, it is all ratio's.......even the spring boxes pivot at a ratio of the fork travel. All of this tends to get overlooked when we look at the behavior and travel of these forks........That's why I feel having a damper that is too stiff has a big effect on the action........My ideal shocker is one that has very little compression damping and not much more on the rebound.

 

[MarBl]

I have now done about 1000mls with the JE Mod. Unfortunately and against Norman's advice I opted not to change from oilite bushings to needle bearings, so my setup still suffers from unnecessary friction.
The AVO 1447 turned out to be too stiff for me. I changed the oil to 5W "like water" (see below) and turned down the valve on my lathe until I got symmetric stroke and rebound on lowest rebound setting, but it still was too stiff, giving my head races quite some heavy beating.
I now reinstalled the armstrong, which was used before and it feels okish concerning stiffness but is symmetric and cant be adjusted.
On the rear I have a Koni 76C-1083 which is much stiffer and does its job well but cant be used for experiments at the front.
I contacted Ikon about 2 weeks ago about their 76-1239, asking for information about optimal valve settings especially for the front. But they did not answer my questions but referred me to the german importer, who has of course no clue about all that and now tries to get the information from the wrong side of the sphere, but didnt call me back yet.
I am planning to change to needle bearings during winter time and hope, the reduced friction then allows the combination with the AVO 1447. But I will still try the Ikon, if I get my hands on a properly valved set. The modified Maughans damper might be an alternative worth considering too.
Things may be a bit more difficult in my case as I am about 80kg, use the bike solo and in 90% of cases without any luggage and for comfortable touring only. It seems to be easier to find a sweet spot, if you are going with a heavier load or prefer a stiffer setup.

 

[greg brillus]

I did not try to strip and re-valve the new Ikon's myself, I figured it would be better to send them back and have them carry out the work. It is a little time consuming to get a result, but from our discussions they seem to be able to do what I want. I don't believe they will supply the modified ones via their own sales listing........they treated my request as if it was a "Customers special" which is fine......It just means that I will need to order a batch to my specs, and then pass them on to folk who might want one. I was trying to come up with a good quality "Ready made" shocker that hopefully had adjustable rebound damping, but the one I tried was still too stiff in its action.........It is not easy to find a shocker to these specs as they are quite small with limited travel........diameter is an issue as well so it does not clash with the upper link. Changing the lower link large bushes to sealed bearings is an easy way to reduce the friction. If you are running a pair of the 45 lb springs, at 80 Kg's you should need to shorten the springs by about 15 to 20 mm each at most to get the small amount of pre-load needed........if the springs are installed as they are, the suspension will sit "Topped out"........ I still can't see how Chris does this with packers as well........I have never done that to any of the bikes I have ever done and some of these have riders in the 120 kg range. Not a criticism, just an observation...........Cheers.

 

[MarBl]

If you are running a pair of the 45 lb springs, at 80 Kg's you should need to shorten the springs by about 15 to 20 mm

I was starting with the soft 30lbs springs provided by tt. Due to the substantial pretension I topped out frequently, so I cut them down to 400mm length and cured the topping out, only to find the bike bottoming out on deep potholes. So I added inner springs, cut down to 300mm length and now its pretty ok, neither bottoming nor topping out and using most of the available fork travel. I think this or a similar combination has already been successfully tested by others.
Maybe one of the german manufacturers (Wirth, Wilbers) can provide a progressive spring that resembles that setup. Thats another task for the next winter season. But the current 4 spring setup (4 spring duck technique?) isnt bad.
I was also thinking about the usage of a standard coil over adjustable shock with similar size and to use this, omitting the outer spring and equipping shrouds instead. I talked to someone who is customising shocks for sidecar use about that idea. The problem we were confronted with, wasnt the length or stroke but the width of the upper lug. Almost all shocks use aluminum and have about twice the width of what is available ( ca. 9mm). So that went nowhere.

 

[oexing]

The girdraulics are not my matter , I was planning to use these older Konis on the rear suspension, Brampton on front. I would not believe that the girdraulics were that stiff in their bushes - provided all bushes were perfectly line reamed and thrust washers perfect. I suspect most of them got their little flaws in decades and certainly an overhaul is definitely a very sophisticated job to get right. When changing for ball bearings - a bit flimsy in my eyes - you possibly just hide deformations in the components by escaping into ball bearings with little friction - and loading all flaws onto them to cope with - for a while.
Anyway, it may be allright like this for long time , but then I would not think you really want excessively low friction in front forks, nor in the rear suspension. These units are responsible for larger and slower motions, very fast smaller loads have to be dealt by tires, by choosing the suitable type plus air pressure inside for road or race use. A girder fork plus the wheel on it is 15 kg or more, the rear unit even more. So easy to see that this kind of mass cannot do fast oscillations at all, the tire has to do it. When messing around with the Konis lately I could have had extra low compression force by no wave washer inside - well, some backlash then. A thinner washer would do then , or add another one or two holes drilled in the piston. BUT I imagined you want some force in compression for preventing the fork to go on top bump stop too fast, so I went for a gut-feel-compromise. Once you made a good tool to undo the top slotted ring nut pressing on a rubber seal you could mod the Koni as you think, don´t know about the Ikons and how to disassemble them with their long shrouds. This seems to be the more economic choice to do for sparing you a lot of shipping risks for finally arriving on a damper you want for your specific application. It is no rocket science and no fancy test equipment required, feel from manual tests should do allright. The younger guys with their teleforks and gas shocks with a multitude of settings of air and oil damping do it by feel and road test, I´d think most of you lot are competent enough to know what suits you . So yes, you can - just do it, have a look and try !!
Another critical point to observe is the alignment of mounting joints, top and bottom, on the bike. You cannot know if all is well, so there might be a side load on the damper by crooked bolts, bushes and all, really some spherical joints would be desirable. Or watch ends when lifting suspension to full travel for detecting sideways motions due to misalignment somewhere. This was no concern while there were two spring boxes at the rear, no damper with its piston rod. We had reports from broken piston rods , most likely from bending loads from misalignments, so check all places for that sort of flaws, or you´ll be sorry later . . .

Vic
compression side with wave washer, 6 holes. Extension 3 holes, adjustable with spiral spring:

extension side with 3 holes plus spring:

 

[greg brillus]

Thanks for the info on the internals of the Koni's Vic, I have just done the same with mods to a Thornton rear shocker, thus now it is better for the front end........Like you say, not difficult........although once you mod some of these parts there is no going back unless you make some new parts. I have several original Koni's here so I might strip one and carry out some mods myself........Just to back up your thoughts on the unsprung weight, the wheels alone are over 30 Kg's complete, not to mention the fork or rear frame component on top of this figure........It is a real battle on classic race bikes, we have a track here that has a very fast down hill run that is very rough........Trying to alter the suspension to cope with this without the forks bottoming under hard braking is the big test. Someone on here mentioned about using progressive springs.......I'm sure I've ridden a Vincent recently with Girdraulic forks, that I believe have this kind of spring in the front cases........the front end felt very smooth and comfortable........This is with a standard front end, but with Thornton shocks front and rear.