Oh No, Not Another Fork Upgrade Thread

[Hobot]

Ludwig i've learned a lot of them INOA dudes have a rough sense of Nortoneering.
I've replaced wheel and stem bearing spacers with alloy tube, used bunch of small cross drilled holes in stem by left the wheel spacers solid. Its tough to make replacement spacers right length clamp up fixed to inner races or not just flail in slack.

hobot

 

[swooshdave]

The earth isn't flat???!?!?

Let's make the assumption that inline holes would be more rigid.

Is it not the case that you want the holes clustered in the lower part of the tube? Thus to get six holes on the lower half the way is to stagger them.

 

[Hobot]

That is easily calculated :
on top of the tube sits a spring with a std rating of 38 lbs/in .
If you set the forks for max travel : 6 " , then 6 x 38 = 228 lbs .
Maybe add a little for spring inertia when hitting a bump ( or a deer ?..) :
250 lbs or 120 kg is the max the tube will ever see .
Any additional load will be taken up by other components .

Duh, smack! oh yeah spring compression. Alas the damper tubes could easy see
way over this as factory spring coil bind about 1/2" before full 6" compression, which would then give a solid slam onto damper tube length. Thanks for the wake up call. Stock R-holders of course slam the damper tube from under side of cap. Peels tubes are Al so could matter on the hole size and geometry. Full 6" range gets full exercise in any ride in-out, but not unpleasant, just uncanny absorbing carrying on.

Its very educational along with almost flat tire to feel how forks and aim reacts to both restricted stem swivel and locked up suspension travel. With stiffened stem swivel you will learn about the sinusoid fork freedome of travel at all times to stay up. With suspension locked you learn about instant transitions between straight>counter>straight>counter steering to try to stay on road with some texture while bike is tending to buck you off w/o any effort on your part.

Keep the developments coming may need em in a 4 wheel trike.

 

[Rich_j]

For the small number of us who have played with home brewed fork mods, thought I'd resurrect this old one as I had something of a eureka moment, well actually more of a doh!

Those of us that have played with RaceTech cartridge emulators, as far as I know, have all struggled to get rebound damping dialled in.
The reason is pretty simple, using the basic instructions from RaceTech which aren't aimed specifically at old Commandos, we remove the rod and cap from the standard forks, arrange some sort of seal to the bore of the stanchion, , drop in the emulator and spring and Bob's you uncle.
Next step is change the oil weight to set up the rebound damping - and that's where it all goes horribly wrong.
It turns out there is actually no way to get any real control over rebound, no matter how heavy you go with oil there's minimal change in rebound.

Racetech instruction refer to damper rod fork installation which is what I assumed Roadholders are, this was pretty much the source of all my confusion.
The style of forks the cartridge emulators are designed for have a check valve in the bottom of the forks to force oil into the damper tube on rebound. The emulators control compression relying on this original feature to control the rebound, bad news is, Roadholders don't have this valve so no way to control rebound once the original rod, cap and valve have been removed.

At this point I actually contemplated going back to stock but my stupidity know no bounds so new parts are underway.

The mod does need a couple of circlip grooves machining inside the stanchion to hold the valve in place.
An interesting option is adding a topping out spring on top of the valve.

 

[Cheesy]

I have to go and pull mine apart now so I can figure out how they do actually work, hard to get my head around it from a CAD model on a Saturday morning. One quick comment though, is it going to be too difficult to get the circlips in and out being so far up the tube?

 

[pete.v]

I have to go and pull mine apart now so I can figure out how they do actually work, hard to get my head around it from a CAD model on a Saturday morning. One quick comment though, is it going to be too difficult to get the circlips in and out being so far up the tube?

I gotta tell ya Cheesy, after studing the diagrams in the manuals and take them apart several time, once to do the Covington upgrade, I still don't really get it. Looking at the Lansdowne units make it a little clearer but the stock damper, well, I dont know. Do what the manuals say to do and all will hopefully work out with the Lords good grace.

Honestly there just isn't enough parts for it to make sense. My word of caution is to keep track of those fiber washers at the bottom of the fork tube.

 

[Rich_j]

The picture below should explain things. It comes from a page on the Racetech site that I stumbled across recently
http://racetech.com/html_files/DampingRodForks.HTML
I hadn't seen this before so could be new.
Well worth having a read of this, gives a good explanation, and compare the diagrams to a our good old Roadholders.

What I'm planning is to retrofit a rebound check valve similar to the diagram and make new damper tube with rebound orifices towards the top as in the diagram.

Getting the circlips in should be pretty straightforward, just expand into the tube and push up until they click into the groove, getting them out could get interesting but I'll cross that bridge later.

 

[AntrimMan]

Is the stanchion inner diameter surface good enough to seal against? I sort of remember mine being a bit swarthy inside. How is your surface finish in side there?

 

[Hobot]

All the stanchions I've seen all of - had same finish top to bottom, but I put and extra buffing on the section the top seal rides on just in case. Inside is unfinished source of most friction and notice it distinctly when smoothed down for spring run/rub.

 

[Cheesy]

The picture below should explain things. It comes from a page on the Racetech site that I stumbled across recently
http://racetech.com/html_files/DampingRodForks.HTML
I hadn't seen this before so could be new.
Well worth having a read of this, gives a good explanation, and compare the diagrams to a our good old Roadholders.

What I'm planning is to retrofit a rebound check valve similar to the diagram and make new damper tube with rebound orifices towards the top as in the diagram.

Getting the circlips in should be pretty straightforward, just expand into the tube and push up until they click into the groove, getting them out could get interesting but I'll cross that bridge later.

Thats a pretty good diagram, another idea for you circlip opportunity (sorry cant help myself Im an engineer after all) could be to have a bottom out spring or rubber buffer in the bottom of the fork so that the stanchion doesnt (cant) go over the shoulder on the damper rod and then move the check valve lower in the tube... just thinking out loud.

 

[Rich_j]

I ran ran a flap wheel down inside the stanchion for the last version, might see if I can get it hard chromed and ground this time.

 

[Hobot]

Hard chrome inside stanchion would be good upgrade for least restriction, for as long as chrome layer might last.

The factory Roadholders bottom hydro stop can be made full function by blocking lower taper holes and moving/staggering them above the taper lip ~3/4-1/4". The top hydro stop becomes nicely silence soft functional by extending the damper rod so damper valve don't hit damper cap. The ~2" slack created can be made useful with a spring spacer of your choice of rate or lost-eliminated by the solid traditional spacers such as Convent shooting self in restricted fork feet. Damper rod clearance in damper cap can allow progressive dampening i found out much to my secure ride pleasure over about anything straight up or laid full over. Much as may rub raw the hi end expensive kits guess which Roadholder kit is the most widely used for the longest so far. It don't take much to improve what factory sold so just saying its better don't mean much to me. Not saying every mod ain't better than mine just plenty good enough for a rough rider over factory issue.

 

[Hobot]

Another way to get back up silent stops is to put spring, rubber cushion above damper valve and fit long enough gaiters they rubber bind on compression.

 

[AntrimMan]

Hi Rich,
chroming inside a hole is a specialized art. Chrome is a line-of-sight process so an anode would need to be inserted into the tube. Then grinding for any appreciable distance up inside the hole will require a carbide quill and special stone for the chrome and even then in the best hands maybe 10:1 for depth/diameter ratio, maybe, without spending a lot of money to go deeper.
The average deck hand and it is going to be miserable.
Go look at Sandvik STS systems. It is a deep hole drilling system which can drill then skive and roller burnish on the pull stroke.
That is the kind of setup that can be successful and is used to make hydraulic cylinders.
Maybe float a DiHart reamer down the hole you have and then follow up with a roller burnish tool.
Start with a half dozen tubes for practice.
I know I sound negative but I'm the fellow who has been there and done that and we had a massive investment in machinery.
The average Joe won't have the gear. I think the hole is there to stay as it is.
How about a deep drawn SS tube thin wall liner instead? or thin wall seamless DOM tubing, perhaps epoxied in place up inside the existing stanchions. Then run a hone in it if you think it necessary.
I'm sorry for sounding so negative but that's what you're up against with chrome inside and grinding. Always try the easy stuff first.
All the best.

 

[Rich_j]

Hi Rich,
chroming inside a hole is a specialized art. Chrome is a line-of-sight process so an anode would need to be inserted into the tube. Then grinding for any appreciable distance up inside the hole will require a carbide quill and special stone for the chrome and even then in the best hands maybe 10:1 for depth/diameter ratio, maybe, without spending a lot of money to go deeper.
The average deck hand and it is going to be miserable.
Go look at Sandvik STS systems. It is a deep hole drilling system which can drill then skive and roller burnish on the pull stroke.
That is the kind of setup that can be successful and is used to make hydraulic cylinders.
Maybe float a DiHart reamer down the hole you have and then follow up with a roller burnish tool.
Start with a half dozen tubes for practice.
I know I sound negative but I'm the fellow who has been there and done that and we had a massive investment in machinery.
The average Joe won't have the gear. I think the hole is there to stay as it is.
How about a deep drawn SS tube thin wall liner instead? or thin wall seamless DOM tubing, perhaps epoxied in place up inside the existing stanchions. Then run a hone in it if you think it necessary.
I'm sorry for sounding so negative but that's what you're up against with chrome inside and grinding. Always try the easy stuff first.
All the best.

No need to apologise, had a feeling it might not be so simple.
I'll get the damping side sorted first and come back to this one, too much to bite off in one go.

 

[john robert bould]

I ran ran a flap wheel down inside the stanchion for the last version, might see if I can get it hard chromed and ground this time.

hard chrome a bore and grind.....good luck,

 

[Hobot]

In practice if ya just smooth it up, ala: the flapper wheel deal or my hick way via dowel and sand paper wrap, & clean up the spring OD, then use forks every now and then and change the hydroscopic fluid yearly or so, then pretty much stays a self burnished smooth operator.

Does anyone know what a restricted fork action feels like? How about stem bearings getting rather stiff? Do ya know what forks do on turning to enter a powered turn?

 

[pete.v]

Does anyone know what a restricted fork action feels like?

I do. Put your stock dampers back in after running the Lansdowne units.