Oh No, Not Another Fork Upgrade Thread

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Rich_j

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Yeas I'm afraid so.

We've done the Covenant and Lansdowne, and Consetino's had a few mentions
So its time for Race -Tech emulators.

These got a mention on the Covenant thread covenant-kit-t4404.html?hilit=race%20tech

Took delivery of this pair today

Oh No, Not Another Fork Upgrade Thread


The plan is to start from scratch and make my own damper tubes from aluminium.
The conversion doesn't use the damper rod but needs a seal between the damper tube and stanchion ID which I can build into the top of the tube.
The bump stop still needs Covenant type conversion so I've ordered a pair of extended bushes from RGM as well as all the standard seals and gaskets.

Will post more pics as the project develops.

(Maxton conversion thread anyone?)
 
Hello..Great to see new inovation, are they adjustable without striping them out :?: Keep the progess coming..Best regards John Lansdowne Eng
 
Rich_j said:
The bump stop still needs Covenant type conversion so I've ordered a pair of extended bushes from RGM as well as all the standard seals and gaskets.
Click to expand...

Rich — I will be very interested to see how you approach this. If I remember correctly from a previous post on the Race Tech emulators, damping was improved but fork travel was increased because the damper rod was discarded, thus potentially increasing the trail and compromising chassis geometry. Doubts have been raised about the effectiveness of the Covenant kit or extended top bushes to provide an effective hydraulic stop (i.e. preventing 'topping out') on full extension. I hope you can solve both of these problems.

Good luck with your experiment and keep us posted!

Dave
 
Ludwig,is working on these.[ good enginner]..I have seen is design, anyone interested can see a diagram on his postings. But looks like a job for the machine shop...What keeps the rebound spring in place.?
 
daveh said:
Rich_j said:
The bump stop still needs Covenant type conversion so I've ordered a pair of extended bushes from RGM as well as all the standard seals and gaskets.
Click to expand...

Rich — I will be very interested to see how you approach this. If I remember correctly from a previous post on the Race Tech emulators, damping was improved but fork travel was increased because the damper rod was discarded, thus potentially increasing the trail and compromising chassis geometry. Doubts have been raised about the effectiveness of the Covenant kit or extended top bushes to provide an effective hydraulic stop (i.e. preventing 'topping out') on full extension. I hope you can solve both of these problems.

Good luck with your experiment and keep us posted!

Dave
Click to expand...


The extended top bush should work, its all a bit of an experiment, we'll see how we go.
 
john robert bould said:
Ludwig,is working on these.[ good enginner]..I have seen is design, anyone interested can see a diagram on his postings. But looks like a job for the machine shop...What keeps the rebound spring in place.?
Click to expand...

I should just say I'm not trying to claim any sort of originality here, this was my starting point http://www.members.shaw.ca/randell/cart ... lation.htm and I have seen Ludwig's posts. He is taking a more ambitious line than myself but I'm pretty new to playing with suspension so taking it in small steps.
Mk1 will be compression damping only - no rebound spring.

My first real concern is how good the surface finish is and what sort of dimensional tolerance there is on the stanchion internal diameter, there wouldn't be any reason for Norton to closely control this, it might be pointless putting a proper seal in there.
 
Hi Rich ,Surface finnish is excellent [cold drawn] you can mini hone to produce an even better finnish if required ,Bore size is 26.1mm on my short Roadie's and commando new tubes. So a nylon piston type ring will last ,{its in oil anyay] you can try a bronze ring.or brass it retains a springy nature ,within limits! ..you can allways fit the Lansdowne kit :wink: and as a forum member receive free post..Best Regards John...ps the long bushes dont do anything..ask L.A.B
 
john robert bould said:
Hi Rich ,Surface finnish is excellent [cold drawn] you can mini hone to produce an even better finnish if required ,Bore size is 26.1mm on my short Roadie's and commando new tubes. So a nylon piston type ring will last ,{its in oil anyay] you can try a bronze ring.or brass it retains a springy nature ,within limits! ..you can allways fit the Lansdowne kit :wink: and as a forum member receive free post..Best Regards John...ps the long bushes dont do anything..ask L.A.B
Click to expand...

Thanks for the fork tube info.
In the standard forks the damper rod limits the fork extension. I'll be removing the damper rod but still need to limit the travel at roughly the same point, hence the extended bushes.
 
john robert bould said:
Hello..Great to see new inovation, are they adjustable without striping them out :?: Keep the progess coming..Best regards John Lansdowne Eng
Click to expand...

Nope. You have to fish them out with bent wire to make adjustments. Compression damping adjustsments are made by the nut controlling spring preload. Rebound adjustment is by changing oil viscosity. It's a bit of a pain to get it right, but once it's done it seems to work quite well. I've fit a set to the Laverda forks on my featherbed/Commando 750 race bike, and they definitely improved the front end, once we got through fiddling with it.

Ken
 
Rich_j said:
john robert bould said:
Hi Rich ,Surface finnish is excellent [cold drawn] you can mini hone to produce an even better finnish if required ,Bore size is 26.1mm on my short Roadie's and commando new tubes. So a nylon piston type ring will last ,{its in oil anyay] you can try a bronze ring.or brass it retains a springy nature ,within limits! ..you can allways fit the Lansdowne kit :wink: and as a forum member receive free post..Best Regards John...ps the long bushes dont do anything..ask L.A.B
Click to expand...

Thanks for the fork tube info.
In the standard forks the damper rod limits the fork extension. I'll be removing the damper rod but still need to limit the travel at roughly the same point, hence the extended bushes.
Click to expand...
Allowing the bush's to "smack " together can produce a excessive oil pressure at this point..Ducans Manx as "bush clashing" and a constant oil weep..Velocette's have a grove machined down the bush..Pressure relief? My guess is during a few "clashe's" oil is pumped between the top bush face and the oil seal,,the grove allows a pressure release? Could be barking up the wrong tree here,,but there is no mention in any editoral's regarding the grove..except " GROVE MUST FACE TO REAR" as the rear is the lowest edge..is the drain idea right? Chow
 
Just recovering from an epic journey home last night, 7 hours to do a normal 50 minute journey, I used to like snow.

Thanks for all the great detail ludwig, my head's starting to hurt a bit.

Picking on some random points raised further up-

The reason for making my own damper tubes was mainly because I quite like doing that sort of thing but there's also a bit of logic.
My plan was to use a standard hydraulic U seal to seal between damper tube and stanchion ID (if I can find one the right size). This will need a proper machined housing at the top of the tube. So if I take a Norvil item I will have to cut the top off it to start with to fit the seal housing, also it will probably have the standard oil holes some of which may have to be plugged while adding more further up the tube. So I pay a lot of money for a nicely machined part then hack and weld it - I'd prefer to start from scratch and get exactly what I want.

The point about the hydraulic lock on full extension blowing seals is interesting, does the Covenant conversion not produce the same effect? I need to think about that one.

On the damper hole positions whether they are better in a straight line is better than at 90 degrees, I'm not sure it can make any real difference. Another one to think about.

Just about to start stripping things down and measuring. I should end up with a nice 3D CAD model which will help check out a lot of other issues.
 
Time for a bit of an update.
As usual other jobs got in the way a bit but eventually got back on the case.

The pile of bits has grown a bit.

Extended fork bushes from RGM:
Oh No, Not Another Fork Upgrade Thread

These are needed to prevent the forks over extending when there's no damper rod to physically limit the travel.

Alloy damper tubes were made up of machined end caps brazed to the main tube:
Oh No, Not Another Fork Upgrade Thread


Damper tube with seal and bushing:
Oh No, Not Another Fork Upgrade Thread


The only real mistake so far was the depth of the groove for the ptfe strip, this was a bit on the tight side inside the fork stanchion so I've left them off for the moment.
I really struggled to find any seals the right size and was about to dump the seals and just use a bush, eventually found a supplier to turn some up to my dimensions - turns out this is pretty common practice in the hydraulic world.

Forks are now fully assembled with 20wt PJ1 fork oil and 25mm of spring preload as a very rough start point, I have no idea if this is even close to where it should be.

There was a good setup guide on the Racetech site so I plan to run through their procedure next.

The final assembly looks something like this:
Oh No, Not Another Fork Upgrade Thread


Oh No, Not Another Fork Upgrade Thread
 
I've had the Mk1 version installed for a little while now doing test runs and trying a few tweaks.

The first error is that I've made the damper tubes a bit too long. The extra length means more oil is needed to keep the the damper valve submerged.

The maximum possible travel without oil is 4.7", real world travel with hydraulic bump stops at each end I was expecting to be about 4.5" but am only managing 3.9" with extreme abuse. I want to get the forks using maximum travel before playing with preloads and damping to end up using 90% of the available travel leaving a small amount to cope with running into brick walls.
Shortening the top bushes should increase the travel but in practice made very little difference so I'm in the process of working out which element is restricting. Starting with shortening the damper tubes to get the oil volume down. I'm also dumping the damper tube wear ring, its not fitted at the moment and seems to work OK.

Other things on the list to try are lighter springs and lower weight oil.

A few CAD bits n pieces

Original damper tube
Oh No, Not Another Fork Upgrade Thread


New version
Oh No, Not Another Fork Upgrade Thread


Oh No, Not Another Fork Upgrade Thread
 
I've been playing with springs, preloads and oil weight for a while now and seem to be a bit stuck.

The Racetech emulators don't have any rebound damping control except for changing the oil weight, the small adjustment spring is for compression damping only.
The problem is the forks are topping out with a very solid clunk. The topping is supposed to be controlled by extended bushes producing a hydraulic lock at full extension (Covenant mod), this is sort of working but doesn't seem progressive enough.

I could keep increasing the oil weight but I'm already at 20 and there's only one grade heavier I can go to but I think this might not be a good direction to go.

Is it the right thing to increase the damping try to prevent the forks topping at all or should I be thinking about keeping the damping lower and just improving the bump stop characteristic?
How do you know when you've got too much rebound damping?
 
John Bould is the guru on Norton forks and he will probably give you a comprehensive reply. In my experience, excessive rebound damping results in the forks pumping down on heavy braking and not releasing, making the tyre skip because the forks are bottomed and can't respond to bumps. Too much rebound damping gives a harsher ride too. With the bike off the stand and with no front brake applied, push the down on the handlebars and immediately release. Too little damping will result in the fork rebounding and then bouncing just a little. I adjust mine so there is no bounce, if you see what I mean. You can feel too much rebound damping by pumping the forks with the brake applied and if they are quite slow to return. This is assuming your fork action is smooth and the stanchions are not binding slightly. I stand to be corrected by JRB on the above.

This works for me on road or track, but I think you could try a setting on the road and repeat till you get a comfortable but controlled ride under a variety of road conditions.

I think you might get over-damped forks in an effort to prevent that maddening clunk on topping-out! That's one of the reasons I bought JRB's Lansdowne Kit — I just couldn't stand it any longer and messing around with the Covenant kit didn't float my boat either.

Dave
 
Rich, you can get 6" travel with silent indefinite but firm slops on rebounds by just enlightening the damper rod so valve don't hit damper tube cap and the top bush can cover the stanchion holes.

You have shot thy self in the forks by making the damper tube holes so large and have lost the opportunity to make progressing dampening to full hydro stop but not staggering the holes in 2 sizes, totaling about 1/4th less vent area a factory.

If you like stock ride height but want both soft compliant short travel zone for the little nuance road texture but progressive bump absorbing, clip out section of factory spring which will stiffen it and slip in appropriate length spring spacer, like a valve spring.

If you size damper tube in cap with tight clearance you can narrow damper tube in area of sag-travel you want little dampening or resistance to motion.

Should be a way to flip a cartridge on top of damper tube to get rebound or compression adjustment and full 6". I've not felt any need in my mild rough riding after above mods. Might like your mods better though so keep at it and sell me a kit in the end to compare notes.

hobot
 
hobot said:
Rich, you can get 6" travel with silent indefinite but firm slops on rebounds by just enlightening the damper rod so valve don't hit damper tube cap and the top bush can cover the stanchion holes.

You have shot thy self in the forks by making the damper tube holes so large and have lost the opportunity to make progressing dampening to full hydro stop but not staggering the holes in 2 sizes, totaling about 1/4th less vent area a factory.

If you like stock ride height but want both soft compliant short travel zone for the little nuance road texture but progressive bump absorbing, clip out section of factory spring which will stiffen it and slip in appropriate length spring spacer, like a valve spring.

If you size damper tube in cap with tight clearance you can narrow damper tube in area of sag-travel you want little dampening or resistance to motion.

Should be a way to flip a cartridge on top of damper tube to get rebound or compression adjustment and full 6". I've not felt any need in my mild rough riding after above mods. Might like your mods better though so keep at it and sell me a kit in the end to compare notes.

hobot
Click to expand...

I think you've got the wrong end of the stick here, this setup has no damper rods, the travel is purely limited by the two sets of bushes. The holes in the damper tube you mention are not designed for damping but to allow free flow of oil displaced by the stanchion into the damper tube, I don't see how changing number or size can affect topping out, there's no progressive blocking of these at full extension? The control is all in the cartridge emulator. A spring loaded valve controls compression and the restriction for rebound damping is through the passages that open up in the emulator (no adjustment possible).

Sorry if I've misunderstood (big edit)

Its not possible to flip the emulator without a lot of reworking (but not impossible), the damper tube seat and spring seat have to be quite different but I'd still be stuck with a very harsh top out characteristic, thinking maybe I need a bump stop spring inside the stanchion working on the damper tube to help, anyone ever done this and how?
 
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