Need fork damper dimension

I'd appreciate it if several people could give me the diameter dimension at the bottom of the fork damper tube (just above the threaded hole). I need an average so I can make up some sleeves to cover up the oil inlet holes. The Inlet holes get re-drilled in the tapered section as on later Commandos so the forks are provided with a hydraulic bump stop.

For possible modifications to go with the newly released turcite bushings.



Jim S

I have 2, .935 and .938.

Oops, might want to re-look, re-think your described moves. Holes below the tapper never get covered by nothing so are useless as the extra toes half way up a horses leg. The simple standard way to plug them is Al or such pegs beat over and smoothed up for cosmetics and nothing can foul them anyway. New holes are made above the tapper lip according to your understanding hydraulics or insights from others. Welding or brazing or JBWelding also works unless ya just like machining for fun. I stagger mine one bigger hole 3/4" up and two smaller holes 1/2" and 1/4" up.
Works a treat on harsh landings or armadillo speed bumps totally silent soft indefinite bottoming.

There is a way to get factor top out to work right too.

Forks on forum here
norton-roadholder-modifications-t3645.html

More than may want to know here
http://www.members.shaw.ca/randell/roadholders.html

jseng1 said:

I'd appreciate it if several people could give me the diameter dimension at the bottom of the fork damper tube (just above the threaded hole). I need an average so I can make up some sleeves to cover up the oil inlet holes. The Inlet holes get re-drilled in the tapered section as on later Commandos so the forks are provided with a hydraulic bump stop.

Click to expand...

Total covering of holes produces a stop as harsh as solid metal-metal effect .oil like steel is totaly in-compressable! try it....drill and ream a 1/2 hole in someting.fill it half full of oil.sqeeze a 1/2 dowl into it [dissplace the air ]and wack it with a hammer, solid! try it without the oil....just the same!

hobot said:

Forks on forum here
norton-roadholder-modifications-t3645.html

More than may want to know here
http://www.members.shaw.ca/randell/roadholders.html

Click to expand...

Original matchless /Norton dampers,
Firstly they will produce excellent results BUt: there's allways a BUT. Providing the Damper piston is a good fit and the rod/cap bore is a correct clearance and the oil is the correct viscisity..then the forks will rebound in some fashion.
But regarding any compression effect ,its Zero.
There is no topping out cushin, and no bottoming out either.. the manual shows the stanchion holes being closed? infact the holes fall short of this by 1in , only by fitting longer damper rods or longer top bush's will this happen...

The Lansdowne Adjustable cartridge system address's the compression issue,plus rebound effect can be pre-set, Cushins are employed to prevent Topping out,
Mike Grey's Comments on this forum,and John Dunn's who is the Norton Owners Club Tec Adviser rated the system 100%, his comments and others can be read on my web
www.lansdowne-engineering.com

This year ; Bonhams Historic racing; Luke Notton 1st ,Duncan 3rd. Palletforce Championship Austen Keer 1st, Jack Ebb 2nd all Lansdowne Equiped manx's...plus Now offered by the holland norton Works as a up-grade...and they are the Guys who only put in the best parts..over 260 sets world wide...need more info ask LAB,or Reggie

Something tells me Mr. Bould knows of which he speaks.

here is what I have, 06-1888 ...
measured several places around the diameter with a Mitutoyo digital vernier, both of mine are within .001" of each other.
The turned surface indicates this is not a qualified diameter.



All the best.

Thanks AntrimMan - thats the dimension I get.

The idea is to provide a complete Norton Fork upgrade kit. I haven't decided if I'm going to offer the alum sleeves yet.

Turcite bushings make the ride smoother with less stickion, wear or friction.

An aluminum spacer fits into the top of the fork leg to provide a hydraulic bump stop by covering up the bleed holes at full extension. This is the "Coventry" stye modifcation. This spacer is split and stretched so it presses in and stays in place but is still easily removable.



Another aluminum sleeve fits over the bottom of the damper tube to plug the unwanted holes and a new oil inlet hole is drilled above the taper as in the photo below to provide a hydraulic bump stop when bottoming (Courtesy Jean for the photo). This spacer is held in place permanently with loctite or JB weld. Some late model Commandos come already corrected with the holes moved upward into the tapered area.



Yes - other dampening systems are now available from other suppliers.

Jim S

jseng1 said:

I'd appreciate it if several people could give me the diameter dimension at the bottom of the fork damper tube (just above the threaded hole). I need an average so I can make up some sleeves to cover up the oil inlet holes. The Inlet holes get re-drilled in the tapered section as on later Commandos so the forks are provided with a hydraulic bump stop.

For possible modifications to go with the newly released turkite bushings.

Jim S

Click to expand...

Love the bush kit. and the split is a good idea I am using oilon {Oil filled nylon] does the material come as cored bar,and ifso what size is it?...i end up with a bag of ribbons from solid bar!

AntrimMan said:

here is what I have, 06-1888 ...
measured several places around the diameter with a Mitutoyo digital vernier, both of mine are within .001" of each other.
The turned surface indicates this is not a qualified diameter.

All the best.

Click to expand...

Love the cad drawings!

thanks Mr. Bould.
I tend to overthink and then miss the obvious so building animated solid models is my helpful way of exploring "what if?"
Boolean subtractions for calculating precise working oil levels are a wonderful benefit of modeling, no sense making a modification for cushion purposes only to find out it isn't working and then taking a long time to determine the oil is not at that level at that particular time to begin with. That's one of my recent discoveries.
Yes cad is wonderful for the likes of me and I still overlook a lot.
Thanks again.
All the best.

john robert bould said:

jseng1 said:

I'd appreciate it if several people could give me the diameter dimension at the bottom of the fork damper tube (just above the threaded hole). I need an average so I can make up some sleeves to cover up the oil inlet holes. The Inlet holes get re-drilled in the tapered section as on later Commandos so the forks are provided with a hydraulic bump stop.

For possible modifications to go with the newly released turkite bushings.

Jim S

Click to expand...

Love the bush kit. and the split is a good idea I am using oilon {Oil filled nylon] does the material come as cored bar,and ifso what size is it?...i end up with a bag of ribbons from solid bar!

Click to expand...

The Turcite is SO EXPENSIVE. Its only available in solid. But its the best material to choose from.

Jim S

Be ware on calculating fluid volume-levels that the air space pumps down and out over a 1/4 mile or so of fork action, so can start out ok to suddenly hydraulic lock up which then magnifies and reverses normal fork steering and bouncing effects. When ya get to ~180 ml level in standard forks, its close to the limit. Tighter clearances can benefit with lighter fluid so should play with that on each new fitting upgrade.

Save a set of the blue bushes for me, will be wanting some later this year. Save the Al spaces for others though.

hobot said:

Be ware on calculating fluid volume-levels that the air space pumps down and out over a 1/4 mile or so of fork action, so can start out ok to suddenly hydraulic lock up which then magnifies and reverses normal fork steering and bouncing effects. When ya get to ~180 ml level in standard forks, its close to the limit. Tighter clearances can benefit with lighter fluid so should play with that on each new fitting upgrade.

Save a set of the blue bushes for me, will be wanting some later this year. Save the Al spaces for others though.

Click to expand...

Steve .
yes the air effect!
As the oil seal is designed to keep oil in,the seal lip face's inwards,which means the lip is acting like a one way valve, the pumping action of the fork could suck air in....agree? But seal against the stanchion on the upward stroke[compression . But i have had a pressure gauge in the fork...and the reverse happens....firstly increased pressure pulse's then dropping off to low ....dont ask i havent a clue ..they should pump up...but dont they vacuum down!

Hi guys in the 70's I had a Yamaha ST 500 which i fitted air caps wich made the front end less likly to bottom out Has any one tried this on a commando and does the air stay inside Its difficalt to get parts in South Africa so I'm always looking for alternative up grades The Rose linkage head steady was a great improvment to the back end Now Ive just to get the front to behave