Commando Fork Cartridge Conversion

I just finished the work on converting a set of Commando forks to take Honda F4i cartridge internals, and thought I'd post some pictures. I won't get a chance to try it out for a while, because I'm also refurbing the rest of the bike, a second MK3 to complement the one I've been riding. I'm not the first guy to do this, but it's my first one. I was inspired by Chris Consentino's conversion for the vintage racers, which removes the external damping adjusters to comply with AHRMA rules. In my case, I didn't need to worry about that, so I manage to keep the Honda preload and rebound damping adjusters. I did have to change the compression damping adjusters by fitting adjustable orifice screws into the bottom bolts, so adjustment requires removing the front wheel and axle. I took a guess at where to set it, and I'm hoping that will be close enough. If not, I'll eventually get it right, and never change it again. I machined some unneeded metal off the cartridges to make them fit into the Norton forks, and made adapters for the ends to allow the oil from the compression damping adjustment bleed to flow, as well as trying to keep some hydraulic bump stop operation. I turned the top caps down to Norton size, and threaded them to fit the Commando stanchions. I used a pair of Kawasaki Ninja 250 springs shortened to fit and to raise the spring rate. The Honda cartridges have more travel, so I added spacers below the upper bushing to provide a hydraulic stop at full extension, and kept the total travel pretty close to the stock Commando.

I'm looking forward to seeing how it works. I didn't make any mods to the slider or stanchion, so if it is a bust, I can always go back to stock.



Ken

Thanks for the write up, Ken. Let us know how they work!

Hi Ken

More pictures please & a little more detail?

Thanks Chris

VFR 750 will also do the job...with some Machine work , A guy a Donnington last year fitted some to a manx...he came in behind 7 riders with my lansdowne Kits. :roll: which made me happy.. Stewart Tonge as replaced his maxton units and recons the lansdowne are better..once set right.
Duncan and Alex finished 2nd and 3rd again with the lansdownes being only beaten by Spike Edwards. Plus Peter Crew won his class, he does well with his RS 125 honda which i converted . placed second ...and only did 1/2 the races!
Kieth Bedford as just ordered his second set for is 350 manx being very pleased with his 500 ..which says it all.
I am producing the Lansdowne kits for the New Peter Williams 750 race rep, with Guy Martin booked to test...soon . should be interesting. :!:
But please bare in mind the Dampers only make GOOD forks better, Worn forks will not be improved ..as a few have found out.

Worn sliders need to be bored out and oversize bush's ,, which i am setting up to do. combined with PEEK bushs . Better than New.

Ken - very interesting and thanks for posting. Can you post some more photos, e.g. the adjustable orifice bleed screws, bottom bolts and adaptors for the bottom of the cartridges? Did you machine the outside of the cartridge body for more clearance inside the stanchion?

I have just finished adapting a set of early Yamaha R6 damping units for a pair of Seeley forks, which as you know are very like Roadholders, hence my interest in your conversion. I haven't had a chance to try them out yet.

I have heard that the standard Honda high speed compression damping is set quite firm and the rebound not so firm and it seems like that from riding them. The fix, so I've read but can't verify, is to remove one shim from the compression stack and fit that to the rebound stack.

Dave

Those shims , to which i have plenty are really useful for lathe tool packers. getting the right tool hight is important :roll:
Dave watch out for the damper location recess in the Original seeley sliders ALL i have done where way out!
The damper retaining pin hole was drilled from the bottom in , it did not end up in the center of the counter bore, thus pushing the damper over. and causing it to bind . Assembly the damper into the leg and check for concentric location , i have a end mill in a long plug to center the holes , the last set was so bad the top nut had been forced over into the stanchion thread , effect was bending the damper rod. The fork became jammed , what surprised me was the guy was a Main Dealer Kawaski work shop forman. When i enquired if he had noticed the issue , he replied " we only deal in Kawaski parts....... that fit, didn't know OLD stuff was that bad!"

daveh said:

Ken - very interesting and thanks for posting. Can you post some more photos, e.g. the adjustable orifice bleed screws, bottom bolts and adaptors for the bottom of the cartridges? Did you machine the outside of the cartridge body for more clearance inside the stanchion?

I have just finished adapting a set of early Yamaha R6 damping units for a pair of Seeley forks, which as you know are very like Roadholders, hence my interest in your conversion. I haven't had a chance to try them out yet.

I have heard that the standard Honda high speed compression damping is set quite firm and the rebound not so firm and it seems like that from riding them. The fix, so I've read but can't verify, is to remove one shim from the compression stack and fit that to the rebound stack.

Dave

Click to expand...

john robert bould said:

Those shims , to which i have plenty are really useful for lathe tool packers. getting the right tool hight is important :roll:
Dave watch out for the damper location recess in the Original seeley sliders ALL i have done where way out!
The damper retaining pin hole was drilled from the bottom in , it did not end up in the center of the counter bore, thus pushing the damper over. and causing it to bind . Assembly the damper into the leg and check for concentric location , i have a end mill in a long plug to center the holes , the last set was so bad the top nut had been forced over into the stanchion thread , effect was bending the damper rod. The fork became jammed , what surprised me was the guy was a Main Dealer Kawaski work shop forman. When i enquired if he had noticed the issue , he replied " we only deal in Kawaski parts....... that fit, didn't know OLD stuff was that bad!"

Click to expand...

I hear you, John, and I want to send you my sliders for you to ream and make new bushes - when Dick Hunt can machine some Manx stanchions for me. While you're at it, I was going to ask you to check the counterbores.

Dave

Dave,
just making the jig to hold the sliders in the lathe for boring, my be-spoke reamer doe's not always clean up. First slider on the lathe is a early short roadholder ,,with 30 thou wear . Its amazing how much the slider's do wear, but after 50 years of water/oil mixed with spring shards ..may by not!

Just a saddle stop to make and i am in business . wont be long before the pro's provide this service :twisted:

daveh said:

Ken - very interesting and thanks for posting. Can you post some more photos, e.g. the adjustable orifice bleed screws, bottom bolts and adaptors for the bottom of the cartridges? Did you machine the outside of the cartridge body for more clearance inside the stanchion?

I have just finished adapting a set of early Yamaha R6 damping units for a pair of Seeley forks, which as you know are very like Roadholders, hence my interest in your conversion. I haven't had a chance to try them out yet.

I have heard that the standard Honda high speed compression damping is set quite firm and the rebound not so firm and it seems like that from riding them. The fix, so I've read but can't verify, is to remove one shim from the compression stack and fit that to the rebound stack.

Dave

Click to expand...

I'll take some more detailed pictures and post them as soon as I can. I didn't have to machine the actual cartridge body, just the top and bottom ends and the rebound spring fitting. I'll post a picture of a stock one for comparison.

I also picked up a set of R6 bent forks as a possible donor, but it looked to me like it was a bit easier to use the smaller diameter Honda internals. I've seen the R6 conversion done, but with custom stanchions in slightly larger diameter.

Ken

john robert bould said:

The damper retaining pin hole was drilled from the bottom in , it did not end up in the center of the counter bore, thus pushing the damper over. and causing it to bind . Assembly the damper into the leg and check for concentric location , i have a end mill in a long plug to center the holes , the last set was so bad the top nut had been forced over into the stanchion thread , effect was bending the damper rod. The fork became jammed , what surprised me was the guy was a Main Dealer Kawaski work shop forman. When i enquired if he had noticed the issue , he replied " we only deal in Kawaski parts....... that fit, didn't know OLD stuff was that bad!"

Click to expand...

Interesting, John. I had a similar problem with the Norvil slider, and came up with the same solution, an end mill in a long plastic plug and with a long extension for a drill motor. The quality control in machining some of these parts was clearly minimal.

Kem

john robert bould said:

Worn sliders need to be bored out and oversize bush's ,, which i am setting up to do. combined with PEEK bushs . Better than New.

Click to expand...

Sounds like a good service, John. I've encountered some stock sliders that were seriously worn out. I was fortunate that I had an unused original Norvil slider and a low mileage MK3 Slider that wasn't worn out yet. As I mentioned in a related post, I was looking at making my own extended top bushes, and examining materials to use. Fortunately, I discovered that I had a set of stock bronze bushes that were a very good fit on the stanchions I was using, so I just used them with some spacers to limit extension.

Ken

Some more details.

Comparison of stock vs modified cartridge. You can see the extra bits that I had to remove. The top washer and the spring seat on the top of the cartridge bottom washers are stepped to locate the spring ends, but that doesn't show in the pictures.



Stock vs Modified top cap, threaded to fit Norton forks.



Closer view of base adapter and bottom bolt.



Closeup of bottom bolt. You can see the adjusting screw protruding into the bleed hole in the side of the bolt.



Another view of the adapter and bottom bolt, showing the hole drilled and tapped in the bolt for a 8-32 set screw.



And a shot of the spacer that limits fork extension to just little more that the stock Commando fork, and provides a little bit of hydraulic action to limit the impact of full extension.



That's about all there is to it.

Ken

Ken - thanks for sharing those pics. Good pics and neat machining. Do I see two shallow oil seals on each fork leg or is it a trick of the light? The fiddly part for me was making the adjustable bleed screws to get a progressive flow of oil from the orifice in the damper retaining bolt as you turn the screw, rather than like an on/off switch. How does the oil return from the bleed holes past the larger diameter of the stepped spacer/hydraulic stop?

I have gone down roughly the same route as you with the Seeley forks except I had to hide my top damper adjusters and consequently had to make new top fork nuts and had to use preload spacers. I will post some pics on this thread shortly as a comparison.

Dave

My Lansdowne cartridges showed up a few days ago and I'm getting ready to tear off the front end, do brake calipers, send out rotors and mount a new tire up front. Spring is right around the corner. I need to sort this thing out.

daveh said:

Ken - thanks for sharing those pics. Good pics and neat machining. Do I see two shallow oil seals on each fork leg or is it a trick of the light? The fiddly part for me was making the adjustable bleed screws to get a progressive flow of oil from the orifice in the damper retaining bolt as you turn the screw, rather than like an on/off switch. How does the oil return from the bleed holes past the larger diameter of the stepped spacer/hydraulic stop?

I have gone down roughly the same route as you with the Seeley forks except I had to hide my top damper adjusters and consequently had to make new top fork nuts and had to use preload spacers. I will post some pics on this thread shortly as a comparison.

Dave

Click to expand...

Can you set them up with zero bleed shim stacks and get rid of the low speed compression adjuster all together?

Can't see how this kit works but wonder if I'm seeing things or is this bolt bent?

daveh said:

Ken - thanks for sharing those pics. Good pics and neat machining. Do I see two shallow oil seals on each fork leg or is it a trick of the light? The fiddly part for me was making the adjustable bleed screws to get a progressive flow of oil from the orifice in the damper retaining bolt as you turn the screw, rather than like an on/off switch. How does the oil return from the bleed holes past the larger diameter of the stepped spacer/hydraulic stop?

I have gone down roughly the same route as you with the Seeley forks except I had to hide my top damper adjusters and consequently had to make new top fork nuts and had to use preload spacers. I will post some pics on this thread shortly as a comparison.

Dave

Click to expand...

Must be the light. There is only one thick fork seal, not two thin ones. It's not a stock Commando seal, but an aftermarket replacement. It seems to have a bit more stiction than the stock ones, and if it turns out to be a problem, I'll replace them with stock seals.

The oil passes through the two holes drilled in the lower part of the stepped adapter and then flows up past the larger diameter. I made the adapter so that there is enough clearance past it for the oil to flow. The actual amount of oil that flows through the bolt is quite small. I considered trying to fit a tapered needle for the adjustment, but decided that a screw that progressively blocks off the two bleed holes in the bolt would work just as well for my purposes. I don't envision having to change the compression damping once I've found the best setting. I think it's much more useful to be able to change preload and rebound damping. These forks are for a street bike, so I don't think I'll be fiddling with them much once I've got them set to suit me. Of course, I could have it all wrong, but if so, the worst that could happen is going back to the drawing board to try again.

I could also have blocked the hole in the bolt completely, and messed with the compression shim stack instead, but I'm hoping not to have to revert to that.

I did consider a design that would let me use the Honda compression adjuster, but that would have required machining the slider and bolting on a block to take the Honda adjuster needle, as well as some tricky machining on the slider to route the bypass oil properly. It looked like a lot of work for little gain, and would also have ruined the period look of the sliders. I'm trying to get modern damping performance without losing too much of the period appearance.

Ken

john robert bould said:

Those shims , to which i have plenty are really useful for lathe tool packers.

Click to expand...

I've read this kind of statement before from you and it still really surprises me. If I'm not mistaken then you use a simple needle valve for your kit, don't you? Now a needle will give a progressive damping curve damping whereas a shim stack can be set to degressive and linear as well. Usually degressive characteristics is needed for suspension damping. I'd be most interested to see how you want to achieve this, I fail to understand this from reading the description on your website.



Tim

Until they make race tracks like the pot holed roads normal in the UK race track performance is not relevant, digressive damping will beat single rate damping (even when adjustable) on pot holed roads.

lcrken said:

I made the adapter so that there is enough clearance past it for the oil to flow. The actual amount of oil that flows through the bolt is quite small. I considered trying to fit a tapered needle for the adjustment, but decided that a screw that progressively blocks off the two bleed holes in the bolt would work just as well for my purposes. I don't envision having to change the compression damping once I've found the best setting. I think it's much more useful to be able to change preload and rebound damping. These forks are for a street bike, so I don't think I'll be fiddling with them much once I've got them set to suit me. Of course, I could have it all wrong, but if so, the worst that could happen is going back to the drawing board to try again.

I could also have blocked the hole in the bolt completely, and messed with the compression shim stack instead, but I'm hoping not to have to revert to that.

I did consider a design that would let me use the Honda compression adjuster, but that would have required machining the slider and bolting on a block to take the Honda adjuster needle, as well as some tricky machining on the slider to route the bypass oil properly. It looked like a lot of work for little gain, and would also have ruined the period look of the sliders. I'm trying to get modern damping performance without losing too much of the period appearance.

Ken

Click to expand...

OK, that answers my questions! I can see your logic about using a flat bleed adjuster and finding the ideal adjustment and then leaving it at that. I view my efforts as an experiment too. I agree also that it would have been a lot of work to make an external adjuster on the fork bottom and it would take away from the period appearance.

I will be really interested to hear how you get on with a road test.