Commando Fork Cartridge Conversion

Very nice marinatlas !!

While troubleshooting I stumbled across a beautiful Commando. so's not to deviate this thread any more see here..

kommando said:

You can't beat the law of Physics, you can use a set of F4i forks with 43mm stanchions coupled with early Yamaha R6 yokes, conversion bearings needed for the headstock. These are the only modern forks long enough to directly replace Commando forks, get rid of the paint, polish the lowers, fit gaiters and they look period but will take the ohlins cartridges.

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The problem I see with that conversion is that the R6 yokes have way less offset than the stock Commando yokes, so using them will result in a lot more trail, making the bike slower to turn in to corners and more likely to want to run to the outside of the turn when exiting under power. It will also be noticeably slower in trying to make quick transitions, like in high speed esses. It's not that it won't work or be rideable, but it won't work as well when ridden aggressively. I bought a set of R6 yokes a few years back with the intention of modifying the offset by machining them to relocate the steering stem location, but found there wasn't enough material in that area to do so, and wasn't happy with the results of welding in more material. I ended making up my own yokes.

I 'm also still trying to keep the Norvil sliders because I really like the look of the period Norvil brake. It is possible to fit 38 mm tubes to the Commando sliders (Steve Maney did it on his race bike), and I am working on doing that with a set of FZR-600 fork tubes. I will still have to make new yokes, but at least I get to keep the Norton look with the with the rest of the front end.

Ken

kommando, I just noticed that you specified "early Yamaha R6 forks". I don't recall the year of the ones I tried, but they had way less offset than Commandos. Do the earlier ones have more offset than the later ones?

Ken

marinatlas said:

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Gorgeous bike, just not the front end look I'm trying for.

Ken

marinatlas said:

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What make/model/year did that front end come off of?

lcrken said:

Gorgeous bike, just not the front end look I'm trying for.

Ken

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Hi Ken, the red one has the early R6 yokes and yes less offset (1"57 or 40mm) , the blue cdo had BMW K100 (K75) yokes with 54 (ish) mm ( 2.12 ish) , but you need to mill the fork holes to 43mm as they were 41mm and some were a bit larger ( Matchless aka Martyn inspired)

lcrken said:

kommando, I just noticed that you specified "early Yamaha R6 forks". I don't recall the year of the ones I tried, but they had way less offset than Commandos. Do the earlier ones have more offset than the later ones?

Ken

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Yes, hence one of the reasons I picked them, plus being a 750 not an 850 frame then a bit less offset would not be amiss anyway.

I used 99 to 02 with 40mm offset

YZF-R6 600 1999-2002 40mm
YZF-R6 600 2003-2004 35mm
YZF-R6 600 2006-2007 30mm

Here is a database useful for front end swaps

lcrken said:

The problem I see with that conversion is that the R6 yokes have way less offset than the stock Commando yokes, so using them will result in a lot more trail, making the bike slower to turn in to corners and more likely to want to run to the outside of the turn when exiting under power. It will also be noticeably slower in trying to make quick transitions, like in high speed esses. It's not that it won't work or be rideable, but it won't work as well when ridden aggressively. I bought a set of R6 yokes a few years back with the intention of modifying the offset by machining them to relocate the steering stem location, but found there wasn't enough material in that area to do so, and wasn't happy with the results of welding in more material. I ended making up my own yokes.

I 'm also still trying to keep the Norvil sliders because I really like the look of the period Norvil brake. It is possible to fit 38 mm tubes to the Commando sliders (Steve Maney did it on his race bike), and I am working on doing that with a set of FZR-600 fork tubes. I will still have to make new yokes, but at least I get to keep the Norton look with the with the rest of the front end.

Ken

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a fellow told me the 38mm could drop in the Norton sliders (but no bush on the top, same as Ceriani) as the Norton sliders are 38mm inside ...........he fits some early cagiva mito 125 stanchions (one is compression the other is damping )

Stock Commando 750 yoke offset is 2.75"/70.125 mm. Early R6 offset of 40 mm is still way less offset, meaning a lot more trail. That's enough to significantly affect handling. But, as I said above, that doesn't mean the bike wouldn't be rideable. I've seen several Commandos with similar conversions that they were quite happy with. Back in the '80s one of my racing buddies fitted a complete Ducati front end to his Commando, with way less offset in the yokes, and it worked well enough for him to be quite competitive. When I was racing my Commando PR, I fitted a set of adjustable offset Spondon yokes and experimented with different offsets. I found that I preferred a setting very close to the stock Commando offset. Different strokes for different folks, eh?

Ken

This thread shows the way I selected the forks and yokes, there are only 2 fixed points, the length of your current forks and the headstock bearing ID. That gives you lots of options, 2nd hand Japanese stuff is dirt cheap if you are patient.

lcrken said:

I found that I preferred a setting very close to the stock Commando offset. Different strokes for different folks, eh?

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If I want to ride a bike that runs rings around any current bike on the back roads and has a light touch even skittish front end then I pick my B44. The 850 Commando will not turn anywhere near as good but is a lot more stable especially at speed. If I ever get to finish this special build and then reveal it, you will then understand why it needs less offset.

kommando said:

This thread shows the way I selected the forks and yokes, there are only 2 fixed points, the length of your current forks and the headstock bearing ID. That gives you lots of options, 2nd hand Japanese stuff is dirt cheap if you are patient.

Finding a compatible modern front end

If you are looking for a complete new modern front end its difficult to know where to start. A good way is to track down part interchange databases, streetfighter and other specials builders forums are a good place to start. There are lots around. This is an example of a fork database...

www.accessnorton.com

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Good to see the details. It's an interesting conversion. Would be fun to go through past posts and collect the different front end conversions that have been shown, and put them all together in one post, if I could just schedule the time to do so.

Ken

kommando said:

If I want to ride a bike that runs rings around any current bike on the back roads and has a light touch even skittish front end then I pick my B44. The 850 Commando will not turn anywhere near as good but is a lot more stable especially at speed. If I ever get to finish this special build and then reveal it, you will then understand why it needs less offset.

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I'll look forward to the details.

Ken

Ken, it will be hard to find another set of off the shelf trees with 70 mm offset to match the 750 Commando, especially a set that will fit forks from either an early R6 or a CBR600 F4i. But the early right side up R6 fork is common on dirt trackers and there is a pretty active bunch of folks making custom dirt track clamps --these are usually in the 55mm offset/4 + inch trail range, but if it's custom you can probably pretty much get whatever you want. I was talking to a guy, Dan Shaw, found at clamps29@hotmail.com, for a set for my Champion framed Triumph 750 Sportsman bike with 38mm Marzocchis, when I quit racing--but that was several years ago and I am not sure he is still doing it. If you look at Vintage Flat Tracker in the "for sale" area, http://www.vft.org/vftforsale2.html or http://www.vft.org/vftforsale2Products.html you will find other guys making them too, or look at http://www.bankeperformance.com/flattrack/clamps.html or http://lazerracing.com/ or http://durelleracing.com/index.php?main_page=index&cPath=94_23_57 for guys making custom clamps. Cost can be a bit high.

And FWIW, since you mentioned getting it to complete corners better, that usually takes some additional swing arm angle to give it more anti squat in the rear. I had a set of Works shocks made in 14 -1/2 inch length to improve my street 850 Commando a bit--it increased the s/a angle and steepened the fork rake a degree or so, too. Still a bit lazy, its an 850 after all, but better, and I put 18 inch Akront rims on it too, for a better tire selection.

Interesting to see the ways you can improve the front suspension on a Norton Commando. But is there much point in doing all that work when the new forks/yokes are still connected to a spindly frame?

linker48x said:

Ken, it will be hard to find another set of off the shelf trees with 70 mm offset to match the 750 Commando, especially a set that will fit forks from either an early R6 or a CBR600 F4i. But the early right side up R6 fork is common on dirt trackers and there is a pretty active bunch of folks making custom dirt track clamps --these are usually in the 55mm offset/4 + inch trail range, but if it's custom you can probably pretty much get whatever you want. I was talking to a guy, Dan Shaw, found at clamps29@hotmail.com, for a set for my Champion framed Triumph 750 Sportsman bike with 38mm Marzocchis, when I quit racing--but that was several years ago and I am not sure he is still doing it. If you look at Vintage Flat Tracker in the "for sale" area, http://www.vft.org/vftforsale2.html or http://www.vft.org/vftforsale2Products.html you will find other guys making them too, or look at http://www.bankeperformance.com/flattrack/clamps.html or http://lazerracing.com/ or http://durelleracing.com/index.php?main_page=index&cPath=94_23_57 for guys making custom clamps. Cost can be a bit high.

And FWIW, since you mentioned getting it to complete corners better, that usually takes some additional swing arm angle to give it more anti squat in the rear. I had a set of Works shocks made in 14 -1/2 inch length to improve my street 850 Commando a bit--it increased the s/a angle and steepened the fork rake a degree or so, too. Still a bit lazy, its an 850 after all, but better, and I put 18 inch Akront rims on it too, for a better tire selection.

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Yeah, that's why I ended up making my own yokes to put modern Ohlins forks on the MK3 I'm (slowly) building. But your point is valid. There are a number of folks out there who will make custom yokes with whatever dimensions one might need. They do tend to be pricey, but probably worth it compared to the time required to make your own, and usually better looking too.

Ken

Stephen Hill said:

Interesting to see the ways you can improve the front suspension on a Norton Commando. But is there much point in doing all that work when the new forks/yokes are still connected to a spindly frame?

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Well, we don't all consider it a spindly frame. But leaving that aside, my experience is that improving the front suspension on a Commando results in improved performance that is readily noticeable on road and track. By my standards, that makes it worth the effort. We're not trying to turn a Commando into an R1 here, just improve it a bit. And maybe have some fun in the shop too.

Ken

lcrken said:

Yeah, that's why I ended up making my own yokes to put modern Ohlins forks on the MK3 I'm (slowly) building. But your point is valid. There are a number of folks out there who will make custom yokes with whatever dimensions one might need. They do tend to be pricey, but probably worth it compared to the time required to make your own, and usually better looking too.

Ken

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The more I think about it, the more that makes sense. Putting larger diameter modern cartridge forks on, whether upside down or right side up, solves the two problems that one experiences in putting modern cartridges in small diameter Norton forks— (1) enough space between the o. d. of the cartridge and the i.d. of the stanchion to allow the free passage of oil as the fork compresses to avoid unpredictably adding to the damping rates, and (2) enough volume in the top of the fork at full compression to make room for all that oil that is necessary to cover the top of the cartridge at full extension and still leave enough air space to let the fork compress normally and fully with only a reasonable amount of air spring effect (rough rule of thumb is say, minimum of 5 inches air space fork fully collapsed with springs out and preferably more like 6+ for street). In my projects putting custom and F4 cartridges in 38 mm forks the internal fork dimensions seemed marginal, with oil height right at or slightly less than 5 inches. I also had a custom Works Performance cartridge in a set of 34mm RD 350 forks (similar in diameter to the Norton fork) and while the cartridge has a small o.d. they had even more of this volume problem—these were fairly short forks, 30 inch axle to top of stanchion, speaking from memory.

And I was impressed with how good a Norton looks with the early R6 forks. Hm.

Larger diameter and improved action are two very different things IMHO.

I have kept the Norton forks, but they have ultra modern Maxton internals, giving vastly improved action. This is very noticeable and has a big impact on rideability and handling. It’s a problem well worth fixing in my mind.

I doubt very much that the stock diameter stanchions flex to any meaningful degree at my riding levels, so I do not see that as a problem that needs solving.

And as a man with a feeble shed, lacking such luxuries as a lathe and a mill, the avoidance of having to make yokes and spindles and etc in order to make different forks fit is nice too !

It would be fun to have a stand alone thread on front end swaps to see what others have done, reasoning behind, outcomes (intended or not), and the compatibility tips and tricks. Quite sure I don't have the pull on the forum to put together a thread that others care about though.

I've got a Brembo twin disc setup on an early Honda Goldwing front end on my Featherbed that I'm quite fond of the outcome (intended or not).