Commando Fork Cartridge Conversion

Hi .
Proof of the pudding. six years ago i was restoring forks for FITFORX , Nothing special rechrome ..seals etc.
The i was asked to replace a pair of Triumph Dampers with the "Roadholder" dampers. To be honest the conversion to norton appeared to make no difference .
So with a basic rig i did some testing, The Norton stock damper is very basic in design ,having FIXED a clearance hole around the rod to restrict the oil flow...I had seen this Hole worn and the rods badly rusted..hence no damping.

Modern dampers with shim stacks where considered , but due to the availability and unit cost the way forward was a "improved" Norton damper.

i drew up a simple valved /needle design [later a two stage anti klonk version ] not as simple as it appears . the ports have to be matched to the damper demand ,the valve springs made to hold the valve on a precision seat at 1 bar .

Rig test was promising , adjusting the Needle gave a variable damping ,and the compression side the same the forks now had a better action.

I obtained a pair of Kawaski gt 750 forks to compare a "poggo" side by side test.

The rebound feels "about" the same when adjusted , but i have the better control on the compression.

Lucky for me Duncan Fittchet had heard about them and contacted me , I made up a set for is GB access Manx and fitted them one sunday.

Who else could give the dampers a shake down ?

Up to using my system Duncan was filling the manx forks with 140 gear oil, in an attempt to stop the excessive dive on hard braking,

He also suffered from pattering which put him off ,
The new system allowed the use of 10 weight oil and the dive was dialed out..and his dreaded pattering know gone . the result was a win over Glenn English at chinney .

Then more wins . Duncan reported a much better front end ,that allowed him the "get on with the job" not concerned about the front any more.

The rest of the Lansdowne Boys wanted the dampers [know 10 bikes fitted] S.Tonge swapped out his Maxton units and his riding improved :?:


I have often quoted Duncans remarks " Simple but effective" and do the business .

I have never stated they are State of the Art stacked shims , with progressive shim control.

Constant at Holland Norton Works give them a good test and Liked them , Placing them on his web as a upgrade..and orders them for his customers .

repeat orders from racers suggest satisfaction .

I had a phone call from a lad that builds tritons for a living...his words where " is that John, i replied yes..he went on to say i have just give a customers bike with your system installed a road test..all i can say they work bloody great, the best Norton fork's i have tested"

So Tintin
In answer to your question.....No shims , no complex valving ..just good old Needles that Amal have used for air/fuel metering for the last 100 years. and still do.

Proof of the pudding is in the eating ... The belt to hold up your pants ,and the lace that stop's you shoe from falling off..simple but effective for the last 2000 years. Just remember a tree branch and a length of twine {english long bow] defeated a 9000 strong French [state of the art] Army :lol:

Cheesy said:

Can you set them up with zero bleed shim stacks and get rid of the low speed compression adjuster all together?

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Cheesy - That's how the 'cooking' Hondas without low speed damping adjustment work. Not ideal. I rode some late 90s and early 00s Hondas and I owned a VFR (alas!) and the front ends would buck over square edged bumps just like a Commando. As I understand it, the oil is flowing through the low speed (adjustable) orifices most of the time, and the valves open when the wheel hits larger bumps/potholes to absorb the impacts. It would probably take a long time and lots of messing around to achieve an optimum damping set up using shim stack valves alone, but I would be interested to hear if someone has done it successfully.

kommando said:

Until they make race tracks like the pot holed roads normal in the UK race track performance is not relevant, digressive damping will beat single rate damping (even when adjustable) on pot holed roads.

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Kommando - Yes, that's my experience too. I think what John's Lansdowne kit offers especially to the racer is firm and controllable low speed compression damping under severe braking on smooth surfaces. What John has managed to achieve is a set up that gives a lot more confidence in the front end than a standard Commando, i.e. there's damping along all of the stroke, in either direction, unlike a standard Commando!

I have yet to hear how the Cosentino kit works on a road Commando. One or two members here have the kit but I'm not aware that they gave any feedback. Only Ludwig, who made his own digressive set up, posted his findings. What I have found is that suspension mods take a lot of time and this is one of the reasons why Lansdowne and Maxton are in business. They have lots of hard data and can make a set up that is close to what you want and should need only minor fiddling with afterwards.

I totally agree with Dave , hitting a pot hole without shim blow off is hard..its sad that the Highways have no money from central government to repair the roads, giving it to other's instead .
My zzr 1100 was no better, crashing into holes with wrist wrenching jolt ....i dont think many forks can respond in 1000th of a second to these conditions . My Mercedes bangs on sleeping policemen :twisted: As dave states ..theres not many pot holes on race tracks ..so this is not an issue.

Dave thanks for your report ..

john robert bould said:

I have never stated they are State of the Art stacked shims ,...

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No, but you were repeatedly bad-mouthing shims which to me appears as a rather paltry attempt to smooth over the inferiority in principle of your design...

And BTW, I disagree on race tracks not demanding degressive damping characteristics.


Tim

Inferior , to what ? Now before you answer, i have replaced a set of maxton shimed type,and S Tonge reports a better fork.. and hes very well regarded...but no doubt you have built, tuned and raced dozens of Manx's :?:
Bad mouthing shims ...? not a tall..when did i say that ? When Peter williams rings i will have a chat to him...someone who knows a bit :lol:

Tintin said:

john robert bould said:

I have never stated they are State of the Art stacked shims ,...

Click to expand...

No, but you were repeatedly bad-mouthing shims which to me appears as a rather paltry attempt to smooth over the inferiority in principle of your design...

And BTW, I disagree on race tracks not demanding degressive damping characteristics.


Tim

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The Cosentino kit is reported to work very well on the track, and so does the Lansdowne. A good progressive system like the Lansdowne will be better than a so-so digressive system because, irrespective of the slow and high speed damping capabilities, they need to be tuned for the bike and rider. This is why I will wait to see how my conversion works in practice before I make any claims. I wish I had access to a suspension dyno.

+1 for that sentiment, Dave. As far as I can tell, Landsdowne and Cosentino conversions both work well, and their customers are quite happy with them. I'm not knocking them at all. I just like doing my own thing where possible. Not to mention the financial aspect. My total cost for this conversion is less than $150, including the cost of the bent Honda forks on eBay. I've ridden race bikes with bleeding edge Ohlins forks, and plenty of Commandos with stock front forks, and a lot in between. I can live with the stock Commando setup, but I'm pretty sure a modern shim stack damper can be set up to work much better on the variety of roads I ride on, from smooth freeways to serious pot holed and patched rural asphalt. The catch here is getting the proper setup. Like Dave, I'll just have to see how it works, and that won't be for a while. I'm building the bike to be ready in time for the North Carolina rally, but it's not real close to being finished yet. For my other MK3, I'm going with the same Ohlins suspension front and rear that Kenny Dreer used. It should be interesting to compare the two.

Ken

Im guessing that the only reason someone would pull out a shim cartridge and replace it with something pretty basic is that they dont know how to set it up or have someone to do it for them. Interestingly if you look on some of the mountainbike forums there is a lot of detail about fork and shock damping and re shimming etc, maybe its because they dont have engines to fiddle with!!

A few pics of the Yam R6 modified cartridges. The only reason I used these was because I got a set of slightly bent Yam forks for €50 from my local breakers and I could not get a pair of Honda items. There was more work involved because, as Ken mentioned, the Honda is simpler, and also because the Seeley forks are a lot shorter, I shortened the damper tubes and damper rods. I also had to make new fork top nuts and new bottom bolts with needle adjusters. Spring preload is with spacers. Like Ken, I machined away any surplus from the cartridges because it is very tight inside the stanchion. Stanchion ID: 26.1mm, cartridge OD: 24mm. I will use 5wt oil as in stock R6. I don't know if oil will flow efficiently in operation considering the narrow gap between cartridge and stanchion. We shall see.


Above, assembly complete.


New bottom banjo bolt with needle compression damping adjuster; new top nuts with rebound damping adjuster hidden under button head allen screw, a la Maxton. Top nut has the same diameter and thread pitch as Commando. Seeley stanchions are almost exactly like Commando units, only shorter.


Adapter for end of damper tube which fits into recess in bottom of slider, with O ring in groove to stop oil weeps.


Detail of rebound valve: the thin, hollow steel tube slides in the damper tube and presses against a spring-loaded needle valve to regulate slow speed rebound damping. No shim stack. High speed damping is fixed.


Fork top nut with rebound adjuster, which has two O rings which seal against the bore of the top nut.




Above, detail of compression valve, showing stock banjo bolt, which has been changed. I had to rethread the end of the shortened damper tube.

Very elegant installation, Dave. I originally planned to use a tapered needle for the compression adjustment, along with an o-ring to seal, but I was running out of space in the bottom bolt to make it all work, so I took the easy way out. If it doesn't work out, I'll probably make a custom bolt to give me a little more room for the adjuster.

I don't know if you'll have a problem with oil flow and a narrow gap. The other R6/Commando installation I know of used made-to-order stanchions with slightly larger OD and thinner walls, so would have a wider gap for the oil movement. He did have to modify the sliders to make it work, which is something I was trying to avoid.

Ken

lcrken said:

Very elegant installation, Dave. I originally planned to use a tapered needle for the compression adjustment, along with an o-ring to seal, but I was running out of space in the bottom bolt to make it all work, so I took the easy way out. If it doesn't work out, I'll probably make a custom bolt to give me a little more room for the adjuster.

I don't know if you'll have a problem with oil flow and a narrow gap. The other R6/Commando installation I know of used made-to-order stanchions with slightly larger OD and thinner walls, so would have a wider gap for the oil movement. He did have to modify the sliders to make it work, which is something I was trying to avoid.

Ken

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Thanks, Ken.

I'm curious to know why he had to modify the sliders to make them work. I would not like to have to do that either!

daveh said:

I'm curious to know why he had to modify the sliders to make them work. I would not like to have to do that either!

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The mods had to do with the way he accommodated the compression damping adjustment.

Ken

john robert bould said:

Just remember a tree branch and a length of twine {english long bow] defeated a 9000 strong French [state of the art] Army :lol:

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Not really a fair comparison John..... The English Longbow was the state of the archery art at the time.....and being used by the best trained and disciplined bowmen of the day ;-) ....they put a huge number of arrows where it mattered....quickly....

Cheesy said:

Im guessing that the only reason someone would pull out a shim cartridge and replace it with something pretty basic is that they dont know how to set it up or have someone to do it for them. Interestingly if you look on some of the mountainbike forums there is a lot of detail about fork and shock damping and re shimming etc, maybe its because they dont have engines to fiddle with!!

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Ease of use can make a product a better choice than another product that demands expert set up to achieve optimum results.

I have a set of Maxton cartridge forks, but in going that route I spent a lot of money and am dependent on how close Maxton were to predicting my needs. Fine tuning them is probably something I can do, making radical change probably not because my own riding/suspension analysis skills are not up to that.

What I can see is that the Lansdowne design allows fairly simple rider testing to get to something that works to where the front end is no longer an issue that limits the rider. That is a good product.

What I suspect is that a set of Maxton (or Ohlins etc.) can be set to optimum performance which may actually be 'better' but that will need to de done with access to days of track time at different tracks with an exert rider AND an expert suspension technician on hand to analyse rider inputs and make adjustment. And no doubt with a the better refinement the set up will be 'wrong' and need more adjustment to suit each particular track or tyre. This is fine if you have the resources. Most never will.

And if your application is road leisure and touring, a system that allows you to do tweeks as you go and settle for what suits your style is the choice for you.....simple to use products rule. Ken has the resources he needs to go the route he is going (knowledge, skill, time and machine tools). I don't. So I fitted something high end...unfortunately they may never get to the 'fit and forget' stage. Or I will just live with them because my riding and analytical skills wont give me good enough direction to improve things.

Yes the Long bow is a poor comparison ,
I would be interested to know what the performance difference between two [Lansdowne-Honda] would be ...But how would it be measured :?: .
The test rig would be very costly,and complex .
The dampers i produce ,are not that simple ; Each side as three stages, first the oil pass's the piston the give a Original Norton type of operation , then the needle gives secondary control .lastly the port bleed closes to produce a 15 mm brake to prevent the top out clonk .

As the fork compress's the fork spring produces increasing oil pressure, slow movements produce little resistance in the damper body, but as the speed of rebound and compression increases the damper responds to the "faster" rate of oil flow ...it's simple . the oil requires time to pass ,the greater the fork action the greater the oil pressure . and the quicker the damper works in relation to oil under more pressure .
Change the oil grade and the whole fork action changes. The first action. piston control changes ,but the needle control varies .and the anti klonk changes.as with most things simple they can be complex when thought about in depth.

Some people consider rebound and compression in different sides a bit off putting, but the stock norton dampers are never the same anyway.



I know that shim stacks are designed to vary and react to the "movement" over different road surface inputs .

SteveA said:

john robert bould said:

Just remember a tree branch and a length of twine {english long bow] defeated a 9000 strong French [state of the art] Army :lol:

Click to expand...

Not really a fair comparison John..... The English Longbow was the state of the archery art at the time.....and being used by the best trained and disciplined bowmen of the day ;-) ....they put a huge number of arrows where it mattered....quickly....

Click to expand...

I have looked at the AMC/Norton/BSA rod damper and Triumph shuttle valve double damped front forks on the bench with oil but no spring. The first problem it highlights is that there is no damping at all when the valve is moving from its compression position to the rebound position and visa versa. This is typically 1/4" movement with no damping, apply that to a racer on a long fast flat corner on a smooth surface and he will feel the bike has no control as the valve swaps between the 2 damping positions for most of the movement. Just separating the 2 damping types into separate legs and applying a non-return valve to start the damping action will show a good improvement in feel on long fast corners.

John, my comment was 'simple to use'

Complex products can be simple to use. A lot of people who produce complex products however, make them complex to use....and then wonder why users don't love them as much as they do....

So, the conversion is done, but now I have the interesting task of sorting out how much 10W fork oil to use. With the differences in damper diameter and length, I don't imaging the stock Norton amount will be correct, and the smaller diameter stanchion and slider mean the stock Honda amount will be way too much. I haven't had this sort of issue before, so I'm just assuming that I should find out how much it takes to at least have the oil level above the top of the damper tube, and work my way up from there, but keeping the level low enough to have at list some air spring effect at full compression. Should be entertaining. All suggestions cheerfully considered.

Ken

Steve,
You are spot on.
There as been many attempts to improve the original Norton damping, welding up holes, re-drilling ,thicker oil etc,
The top out clonk was addressed [hopefully] by longer top bush's or sleeves .. the original design as no compression control or anti-clonk .
Duncan had a brand new Manx for Goodwood ,at Donnington he compared his GB Access Manx with the Goodwood bike and found the Goodwood bike pattered badly..The lansdowne set cured this. because the fork action was now controlled in both directions .

The constant attack from forum members makes me wonder why, :?: I suggest to my critics to design something better, not to just adapt some Jap units , i personally challenge anyone to produce a new design....from scratch ..go on get the pen and paper out . impress me :!:

lcrken said:

So, the conversion is done, but now I have the interesting task of sorting out how much 10W fork oil to use. With the differences in damper diameter and length, I don't imaging the stock Norton amount will be correct, and the smaller diameter stanchion and slider mean the stock Honda amount will be way too much. I haven't had this sort of issue before, so I'm just assuming that I should find out how much it takes to at least have the oil level above the top of the damper tube, and work my way up from there, but keeping the level low enough to have at list some air spring effect at full compression. Should be entertaining. All suggestions cheerfully considered.

Ken

Click to expand...

I had this problem as well. I referred to the Maxton set up on my Cerianis as a starting point. They specify 5wt oil and an air gap of 150mm with the fork leg fully compressed and no springs. Yamaha specify 5wt oil for their cartridges, so I am starting from those baselines. The oil height/air gap was one of the reasons I shortened my cartridges. The Seeley fork is so short, I would have had very little air gap otherwise, if the damper was to be fully submerged in oil. At the moment, with a 150mm air gap, it looks like I have enough oil over the top of the cartridge. It doesn't cavitate when I pump it up and down on the bench, which I guess is a start! So if it turns out that it isn't enough in practice, I can probably put in a little more without making the air spring too strong.

I assume Honda specify 10wt oil in their Showa cartridge forks?

Would you think of asking Kenny Cummings, who runs a Cosentino kit in his Seeley Norton? If he can give you some data, I would be interested as well!