- Joined
- Jul 2, 2015
- Messages
- 272
Hi, everyone:
I’m the second owner of a Matchless G15-CS, and am in process of getting it back on the road. Engine’s now running, rear Cerianis rebuilt, and I’ve turned to the forks. It’s my first Norton experience altogether; previously worked with my Royal Enfield and have some tangential suspension fork experience from downhill mountain biking. Never worked with this type of plunging damper arrangement, and converted the Enfield fork with a cartridge emulator.
I’m posting seeking:
1) Clarification on the operation of the Roadholder fork in general and the G15-CS/N15-specific Roadholder
2) Advice/confirmation on useful alterations to my G15-CS fork.
Here are what I believe to be the relevant elements of the fork which differ slightly from regular Roadholders based on the parts book and what I’ve seen online.
Fork Internals Labeled by Mick Doul, on Flickr
A: Large hole in stanchion (2 located 180 degrees opposite, approx. 11mm/.450” diameter)
B: Small hole in stanchion (2 located 180 degrees opposite, approx. 3mm/.115” diameter)
C: Tiny hole in upper damper tube (approx. 1.5mm/.055” diameter)
D: Small hole in upper damper tube (Approx 2mm/.090” diameter)
E: Small hole in base taper of damper tube (Approx 2mm/.090” diameter)
Approx sizes are for identification/orientation only and not meant as a basis for any math!
Other differences include:
External main fork springs
2019-12-10_09-05-27 by Mick Doul, on Flickr
A narrower damper rod (.310 inches vice .375”) with a differing top cap arrangement (bushing held into top of damper tube by spring clip vice screw-on cap; my fork has a nice fit between the rod and the bushing; slides easy but very little slop.)
2019-12-10_02-40-54 by Mick Doul, on Flickr
Probably a different damper
2019-12-10_02-39-32 by Mick Doul, on Flickr
So, to try and explain the operation to myself as I play with the disassembled leg, I’m envisioning the fork operation in this manner:
-Fork at encounters bump, forcing stanchion down into slider against spring pressure
-Stanchion base encounters oil in slider
-Oil begins flowing through gap between damper tube and stanchion base nut, damping movement
-Oil begins flowing up through hole E into damper tube
-Damper encounters oil in tube, further damping movement due to brass valve restricting flow
-Oil flows out of holes A and B into space between top and bottom bushings
-As stanchion base nut decends over the taper, increasing pressure/resistance from oil mitigated by hole E, possibly providing the correct cushion against bottoming out.
-Main spring rebounds, and damper travels back up tube
-Negative pressure pulls oil out of space between bushings through holes A and B, fairly unrestricted through the big holes
-Oil in damper resists extension, against the top “cup” of the damper valve
-This oil begins flowing out of holes C and D as the cup pushes up on it
-At top-out, damper (is supposed to) encounter a small cushion of oil in the tube
-Oil drains back to base of slider through all other holes/spaces
Where do I have this wrong? I know it’s not completely correct, especially the oil flow at top-out. The blanking-out of holes as the stanchion passes them has something to do with it, I'm guessing. Appreciate anyone taking the time to clarify this for me.
To point 2:
Previous owner complained of harsh top out. I haven’t noticed any in gentle riding around the neighborhood, but it would clank if I bounced on it hard.
I ordered the JSM sleeve kit to help correct the issue, but Jim was unable to tell me if I needed to relocate hole E, as is done with his mod package on the standard roadholders. Given that there’s no step in the taper and the hole is located at the apex, I am now thinking it can stay.
Planning on the recommended 20wt oil for the reassembly.
So, can anyone explain the exact effect of covering over hole A with a sleeve or longer tophat bushing and/or the plugging of hole B? I’m not sure of their function in buffering top-out action.
Does anyone believe there is a better course of action for this fork, or additional work aside from installation of the JSM sleeves, such as plugging holes C and/or D? Tests I can do? Jim recommended testing the flow through the damper using a bucket of fork fluid, which I should be able to do, but to inform these tests, I’d like to know exactly how the fork is supposed to work and any experienced opinions on what could improve it.
I really appreciate everyone’s consideration in helping me out.
-Mike
I’m the second owner of a Matchless G15-CS, and am in process of getting it back on the road. Engine’s now running, rear Cerianis rebuilt, and I’ve turned to the forks. It’s my first Norton experience altogether; previously worked with my Royal Enfield and have some tangential suspension fork experience from downhill mountain biking. Never worked with this type of plunging damper arrangement, and converted the Enfield fork with a cartridge emulator.
I’m posting seeking:
1) Clarification on the operation of the Roadholder fork in general and the G15-CS/N15-specific Roadholder
2) Advice/confirmation on useful alterations to my G15-CS fork.
Here are what I believe to be the relevant elements of the fork which differ slightly from regular Roadholders based on the parts book and what I’ve seen online.
A: Large hole in stanchion (2 located 180 degrees opposite, approx. 11mm/.450” diameter)
B: Small hole in stanchion (2 located 180 degrees opposite, approx. 3mm/.115” diameter)
C: Tiny hole in upper damper tube (approx. 1.5mm/.055” diameter)
D: Small hole in upper damper tube (Approx 2mm/.090” diameter)
E: Small hole in base taper of damper tube (Approx 2mm/.090” diameter)
Approx sizes are for identification/orientation only and not meant as a basis for any math!
Other differences include:
External main fork springs
A narrower damper rod (.310 inches vice .375”) with a differing top cap arrangement (bushing held into top of damper tube by spring clip vice screw-on cap; my fork has a nice fit between the rod and the bushing; slides easy but very little slop.)
Probably a different damper
So, to try and explain the operation to myself as I play with the disassembled leg, I’m envisioning the fork operation in this manner:
-Fork at encounters bump, forcing stanchion down into slider against spring pressure
-Stanchion base encounters oil in slider
-Oil begins flowing through gap between damper tube and stanchion base nut, damping movement
-Oil begins flowing up through hole E into damper tube
-Damper encounters oil in tube, further damping movement due to brass valve restricting flow
-Oil flows out of holes A and B into space between top and bottom bushings
-As stanchion base nut decends over the taper, increasing pressure/resistance from oil mitigated by hole E, possibly providing the correct cushion against bottoming out.
-Main spring rebounds, and damper travels back up tube
-Negative pressure pulls oil out of space between bushings through holes A and B, fairly unrestricted through the big holes
-Oil in damper resists extension, against the top “cup” of the damper valve
-This oil begins flowing out of holes C and D as the cup pushes up on it
-At top-out, damper (is supposed to) encounter a small cushion of oil in the tube
-Oil drains back to base of slider through all other holes/spaces
Where do I have this wrong? I know it’s not completely correct, especially the oil flow at top-out. The blanking-out of holes as the stanchion passes them has something to do with it, I'm guessing. Appreciate anyone taking the time to clarify this for me.
To point 2:
Previous owner complained of harsh top out. I haven’t noticed any in gentle riding around the neighborhood, but it would clank if I bounced on it hard.
I ordered the JSM sleeve kit to help correct the issue, but Jim was unable to tell me if I needed to relocate hole E, as is done with his mod package on the standard roadholders. Given that there’s no step in the taper and the hole is located at the apex, I am now thinking it can stay.
Planning on the recommended 20wt oil for the reassembly.
So, can anyone explain the exact effect of covering over hole A with a sleeve or longer tophat bushing and/or the plugging of hole B? I’m not sure of their function in buffering top-out action.
Does anyone believe there is a better course of action for this fork, or additional work aside from installation of the JSM sleeves, such as plugging holes C and/or D? Tests I can do? Jim recommended testing the flow through the damper using a bucket of fork fluid, which I should be able to do, but to inform these tests, I’d like to know exactly how the fork is supposed to work and any experienced opinions on what could improve it.
I really appreciate everyone’s consideration in helping me out.
-Mike
Last edited: