Norton Roadholder modifications

Classic Norton Commando Motorcycles.

Norton Roadholder modifications

Postby Jeandr » Sat Apr 04, 2009 7:12 pm

Roadholder fork modifications:

The first thing to do is to dismantle the forks completely, I will not go ianto a detailed step by step "how to", this has been posted before and most manuals have a good description of how to do it.

The first thing to do is to plug up the holes at the very bottom of the damper tubes, on the older shorter damper tubes, it is easy to do with an aluminum sleeve of the correct size. On my damper tubes, I turned down the end a bit to make it really round and made little sleeves that I pressed on. On the Commando damper tubes, the hole is midway up the taper, plugging those is best done by tapping the holes for a 1/8" pipe plug and gluing it in place before filing down the excess outside the tube (be carefull about not making the hole too big and getting material inside the tube, I haven't done this myself, but I guess it can be done fairly easily)

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Next the holes must be relocated to a point just above the taper. By doing so, a proper hydraulic slowdown is acheived.

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Next the stock damper rods will need to be replaced with rods that are 2" longer than the original ones. Greg (a.k.a. NORBSA) makes a kit of parts that includes longer alloy rods, he can be reached at norbsa@hotmail.com

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Now on to the springs, the regular Norton springs are 18.5" in lenght and get coil bound (will not compress anymore) at 13.25" for a total possible travel of 5.25". The commando forks and even the shorter Atlas forks all have a possible travel of 6.25". This is considering going all the way to the bottom and extending the sliding and fixed bushing contact each other. An unmodified fork has about 4.5" of travel before things click and clank.

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To gain more travel, a "helper" spring is added to the now longer rod, this allows more than 6" of travel before the main and helper springs get coil bound, Greg has parts similar to these in his kit. The combination of the stock spring and a helper spring works well on Commandos according to Greg, however on the shorter Atlas forks, these springs get coil bound before full possible travel is acheived, but there is a way out by fitting progressive springs (Greg has some), these progressive springs have a free lenght of 19" and get coil bound at 11" which provides more than enough range for Atlas forks and they would probably enhance the handling of Commandos as well.

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The stock Norton damper tube cap is made out of aluminum, it is reccomended to use dissimilar metals when they rub on each other, this is why I made bronze damper tube caps although one of my friends told me not to worry since the whole assembly is running in oil and there is not that much movement and no side loads. At any rate, these bronze caps are available from Clubman Racing (I made mine)

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Here are the fork innards all appart:

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Now to keep the oil inside the forks, a stock Norton oil seal can be used, but I have heard very good reports of a brand called "Leak Proof Fork Seals" http://www.motohaus.com/html/seals/leak ... 0intro.htm To use these, the top hat bronze bushing in the forks must be modified by filing grooves to allow oil to get under the seal

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The fork leg must also be very clean and free of gunk and debri since the seal can move up and down. There are lips on both the inside and outside of the seal so good surfaces must be present on both the fork leg and the fork tube. Obviously the fork tube moves much more so it must be in very good condition, free of bumbs and pits.

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By doing these modifications, the forks should have 6" of travel and a soft compliant ride. The forks will extend more than the stock ones but will settle down 1 to 1.5" when sitting on the bike, this gives a possible 4.5" of compression damping and 1.5" of rebound damping, and there is proper hydraulic control of both compression and rebound.

Comments welcomed

Jean
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Postby daveh » Sun Apr 05, 2009 6:01 am

Jean — very interesting, and thanks for sharing it with us. A few questions:

1. The first photo shows the right hand tube which has been relieved just above the boss that goes into the bottom of the fork alloy. What is the reason for this?

2. I can see how you get a better hydraulic lock on compression by relocating the hole in the damper tube, but I don't see how you improve the hydraulic lock on extension. I thought you had to extend the top bushes to do this. Or have I missed something? Please explain.

3. What is the steering geometry like with your fork mod? Have you measured the height of the front end compared with standard? If it sits higher, assuming you retain the standard rear shocks, surely this will result in slower steering? Or have you made it with enough static sag that it is the same as standard?

4. What grade and quantity of fork oil did you end up using per leg with the mod?

5. Stiction is a problem on these old fork designs. Has yours improved with the new seals? Would you contemplate making bushes from oil impregnated plastic, like Maxton does?

Dave

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Postby Jeandr » Sun Apr 05, 2009 7:51 am

daveh wrote:Jean — very interesting, and thanks for sharing it with us. A few questions:

1. The first photo shows the right hand tube which has been relieved just above the boss that goes into the bottom of the fork alloy. What is the reason for this?

2. I can see how you get a better hydraulic lock on compression by relocating the hole in the damper tube, but I don't see how you improve the hydraulic lock on extension. I thought you had to extend the top bushes to do this. Or have I missed something? Please explain.

3. What is the steering geometry like with your fork mod? Have you measured the height of the front end compared with standard? If it sits higher, assuming you retain the standard rear shocks, surely this will result in slower steering? Or have you made it with enough static sag that it is the same as standard?

4. What grade and quantity of fork oil did you end up using per leg with the mod?

5. Stiction is a problem on these old fork designs. Has yours improved with the new seals? Would you contemplate making bushes from oil impregnated plastic, like Maxton does?

Dave


1- the original has this releif, but the surface is not smooth so I just made it smoother for my sleeve to fit better.

2- On rebound, there is no "lock" but by making the rod longer, it "pumps" more oil so it has a better chance of doing its job before the two top bushings contact each other on full extension. If you extend the top bushings, you reduce the possible travel of the forks by the lenght of the added bushing.

3,4 and 5 - I am on the building stages with my café racer ( see http://www.pbase.com/jeandr/cafe_racer for a photo "blog" of my progress) but according to Greg the ride is not higher, all you are doing with these mods is extending the fork travel and making the forks operate nearer the middle of the range as well as adding a proper hydraulic damper on compression, all these points are missing on unmodified Roadholders, this is why it is common to hear them clang on extension as well as compression. The same quantity of oil is required, I plan on using ATF since it is easier on seals.

As for stickion, the Leak Proof Seals are supposed to cure that, they are softer and more compliant than regular seals. Keep in mind that proper clamping of the pinch bolts for the fork and the axle will also help the forks to operate smoothly. I will have to look at those plastic bushings.

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Postby RennieK » Sun Apr 05, 2009 1:24 pm

A very interesting and informative post. Thanks for sharing!
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Postby daveh » Sun Apr 05, 2009 4:16 pm

Jean — thanks for your reply. I guess the best thing for me to do is try it out. It wouldn't cost too much in any case. I already have new RGM-supplied damper tubes with the hole in the right place, so all I would need are the extended rods, since I have spare springs.

Here's one link I found to self-lubricating plastic:
http://www.gcip.co.uk/EP/materials/nylo ... lled_Nylon

I will be making further enquiries about this next week. I can post the results if you are interested.

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Postby Jeandr » Sun Apr 05, 2009 7:46 pm

daveh wrote:Jean — thanks for your reply. I guess the best thing for me to do is try it out. It wouldn't cost too much in any case. I already have new RGM-supplied damper tubes with the hole in the right place, so all I would need are the extended rods, since I have spare springs.

Here's one link I found to self-lubricating plastic:
http://www.gcip.co.uk/EP/materials/nylo ... lled_Nylon

I will be making further enquiries about this next week. I can post the results if you are interested.

Dave


Sure, the more we all know about Norton forks, the better we can make them work. That Oil filled nylon looks like a good material for fork bushings. Both bushings could be replaced with those, the forks could have an even better softer ride.

I have to give a big thanks to Greg (norbsa) he did all the work for Commando forks, all I did was to find out what needed to be done to get the same results on earlier Atlas forks.

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Re: Norton Roadholder modifications

Postby Caferider » Wed Jan 19, 2011 9:40 am

Jean,

Thanks for the good work, you saved me lots of headaches.
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Re: Norton Roadholder modifications

Postby Jeandr » Wed Jan 19, 2011 11:48 am

Caferider wrote:Jean,

Thanks for the good work, you saved me lots of headaches.


Thanks should go to Greg (aka norbsa), he is the one who developped all these mods and was gracious enough to let me post them. He sells a kit of parts for those who can't make their own and can be reached at norbsa at hotmail dot com

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Re: Norton Roadholder modifications

Postby norbsa48503 » Wed Jan 19, 2011 12:12 pm

With the Atlas set up if you use Progressive springs for Commando's and new rods the kit is cheaper (no make up springs). So 55.00 for the kit and 30.00 for the Dampner caps and your set. You use a 1/16 pipe tap and socket head plugs to stop up the old dampener holes.
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Re: Norton Roadholder modifications

Postby Foxy » Wed Jan 19, 2011 3:10 pm

Gday Jean, as always your post are very good to excellent like this one. Im fitting the longer top brass bushes to my Roadholders
and also the impregnated Leak proof seals. I hadnt heard of fileing the grooves in the top of bushes for seal lubrication and Ive not long finished making bottom bushes out of Ertalon, one of those oil filled Nylon products.All to complement the Landsdowne kit.
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Re: Norton Roadholder modifications

Postby hobot » Wed Jan 19, 2011 10:33 pm

Hehe, if ya like these fork mods wait till you try a rear rod linkage! It took some arguing with Greg before he believed 6+ inch stroke possible in Roadholders.

The taper part of damper does nothing, just weld or JBWeld seal the holes and clean up for peaces of mind. This is many decades old upgrade to get soft hydro stop. Past kits supply Al dowels you slip in and hammer both ends over.

The new holes work better if placed 3/4"-1/2" above taper lip as by time the stanchion end is slammed down to cover a hole right at the lip - its too late to damper much of the stanchion slam bam. MIght re-try with two small staggered holes, at 3/4" up and 5/16", then one normal size hole at 1/2" above. Delicious progressive sense of stop that is so soft its indefinite when it bottom to rebound.

For decades now Convent kit - bush extension-spaces slipped on stanchions below the top bushes so with only 4" of fork extension the stanchion holes get covered to cushion the top out.

Also for decades longer damper rods installed to stop the clack of valve hitting Al damper cap. But then the factory springs coil cant extend that far so Solid Spacers were used to stop spring slop but also limited travel to factory 4" and still a solid extension Stop.

Trick is to use a Spring Spacer, Trickier is to play with the spring rating. Softer sags to factory height, harder lifts fork more when pilot seated. Trickiest is to play with several sections of various spring rates for progressive action as desired. Keep in mind shortening a spring ups its rating.

My favorite fluid after trying a wide scope is plain ole power steering fluid.
Remember the forks pump out air pocket after 1/4 mile or so, so if really pushing fill limits you can suddenly have hydro locked forks. This both magnify fork reactions to slight road imperfection Dramatically, it also Reverses the fork input reactions for even More Drama to stay in control.

Note that Al 10mm damper rods are thicker than factory so that also helps dampen d/t the thinner space in damper cap hole. I saw the light and sanded down a few thousandth's shallow in Peel's Al rods for ~2" length, 'valley' centered on the sag level with me and 1/2 fuel load. This give less dampening freer motion to the slight nuance road imperfections, fork don't jar going over THE Gravel, but on inch up or down beyond that dampens very nicely thank you.
Greg provides new damper caps with some of above in mind.

Can thread the top of damper rod further down to gain a bit more anti-sag preload w/o stacking washers which interfere with fluid filling.

Then may have so much secure fun you can run into the fork twist up-twist
rubber band connection to the tire patch reaction. I highly recommend RGM brace that sort of helps extend the bush space support at full extension.
But I've tested just short of fork bending impacts at full extension and find there is so little spring resistance and little striction the forks instantly compress to any force before they can even be impacted in full extension.
Its a total non issue short of impacts that will destroy forks no matter what.

About the greatest source of striction is the springs budging to rub-bind inside stanchions, not the slick bushes. It distinctly detectable worthwhile to half ass smooth polish the outer coils and inside of tubes.
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Re: Norton Roadholder modifications

Postby ludwig » Thu Jan 20, 2011 3:05 am

Jeandr wrote:.. no side loads..

Only when the damper rod sits perfectly concentric in the stanchion , wich is not a given thing ..
When not concentric , you get extra friction and rapid wear of the damper cap .
New damper caps are nice , but on rebound , far more oil escapes downwards past the floating piston ( cup ) , wich has a clearance of 0.35 mm ( 0.015" ) .
You could consider making pistons with less clearance .
In a STD roadholder , compression damping is almost non existent .
The squared off washer allows too much oil flow .
IMO, Improving the damping is more rewarding than increasing travel ..

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Re: Norton Roadholder modifications

Postby kommando » Thu Jan 20, 2011 4:16 am

There are a couple of issues with the extended travel which need to be considered.

1. The extra travel will allow the front wheel to drop futher when on the center stand so both wheels may still be on the floor, so the centerstand may need modifying.

2. I have seen a post or message somewhere saying the Norton alloy fork bottoms are too weak to accept the longer travel and cracks can occur. No idea if that is valid or just hearsay and if the static point is unchanged it unlikely IMHO.
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Re: Norton Roadholder modifications

Postby norbsa48503 » Thu Jan 20, 2011 7:44 am

When I do BSA dampener modifications I start by driving a polished and hardened rod inside the dampener tube several times to get the hour glass shape out and smooth the finish in the bore. Very labor intensive duty this job is. Than I can make and fit new valve (star type) washers and upper bushings with much tighter tolerances. The cups don’t seem to need tightening up of their tolerances to work well. A little hole moving like on the Norton and all is well. But BSA never used the dampener rod and the fragile valve at its end for a fork stop so you don’t find them in pieces in the bottom of the sliders. To me doing this was a bad move and still is, I found a way to make it all work and not let it beat itself to death without spending hundreds of dollars. Yes with this modification on a Norton when it has no load on, the sliders move downward more than they did as stock to some it a problem to others it is not. The extra travel and oil flow holes being moved get the oil doing the work well, a fix that works for most. There are three hundred kits out there no one has wrote back to say there was a problem.
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Re: Norton Roadholder modifications

Postby hobot » Thu Jan 20, 2011 3:46 pm

Yes center stand won't lift rear unless stand first put on ~1" block.
The real life issue when really needing-using the full 6" stroke is mudguard can collide with the headers. The fully functional hydro stops spread the shock loads to the whole slider area so no problemo as can happen by metal to metal focused contact. Forks must be turned some at speed when hitting this hard of course.

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Greg, I seek your advice on the damper valve diddles. I can't tell anything hindering Peel's RoadHolders so far but want to try -the drop on top of damper tube rebound cartridge- in one leg to see what that's like. Will have to cut down damper tube to keep the full travel though. I've seen some neat mods done to the Norton damper valve mimicking the spring loaded flapper cartridge. Do you offer something yet for that ole plunger action.
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