Fork Yokes (Triple Trees)

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Hi All,
Tonight's stupid question is :D
What is the difference between the late featherbed fork yokes and early commando yokes? I've read somewhere the angle (trail) is different, but doe's it make any real difference to handling and what would I be better off buying?

Thanks

Webby
 
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They are the same. Early Featherbed yokes were 7" wide, then they moved to 7 3/8" for the later Featherbed and early Commandos.

Jean
 
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The width is the same at 7 3/8" but the offset is substantially different. Featherbed yokes have 2 1/4" offset and commando yokes have 2 13/16" offset. One of the reasons why a Commando is less agile than a featherbed framed bike.
 
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johntickle said:
The width is the same at 7 3/8" but the offset is substantially different. Featherbed yokes have 2 1/4" offset and commando yokes have 2 13/16" offset. One of the reasons why a Commando is less agile than a featherbed framed bike.
Isn't that only on the newer style yokes (with hex head cap screws) :?: That change came because they switched from a 3.00 X 19" tire to the (goofy looking) 4.10 X 19" no :?:

Jean
 
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johntickle said:
The width is the same at 7 3/8" but the offset is substantially different. Featherbed yokes have 2 1/4" offset and commando yokes have 2 13/16" offset. One of the reasons why a Commando is less agile than a featherbed framed bike.
Thanks JT :)
Did you not have some Norton parts for sale on e bay recently?
Also, where are you in Belgium? I used to live there, in fact there's a very good chance I'll be moving back soon :)

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Jeandr said:
johntickle said:
The width is the same at 7 3/8" but the offset is substantially different. Featherbed yokes have 2 1/4" offset and commando yokes have 2 13/16" offset. One of the reasons why a Commando is less agile than a featherbed framed bike.
Isn't that only on the newer style yokes (with hex head cap screws) :?: That change came because they switched from a 3.00 X 19" tire to the (goofy looking) 4.10 X 19" no :?:

Jean
Thanks Jean,
I'll do some more research and see what I can find, I'll let you know if the early ones are the same :)

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Johntickle wins the prize :D
Looking though the RGM catalogue, they list the Featherbed yokes as having 2 1/4" offset and the Commando at 2 13/16".

Webby
 
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not-ron said:
Excuse my ignorance but why are they called triple trees ? :x
Why do clocks turn clockwise? In French, they are called "T de fourche" which does not translate well into "fork T"

Jean
 
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Jeandr said:
not-ron said:
Excuse my ignorance but why are they called triple trees ? :x
Why do clocks turn clockwise? In French, they are called "T de fourche" which does not translate well into "fork T"

Jean
Quite true Jean, you've only touched the top of the iceberg there, there are many other motorcycle parts and tools in French that do not translate well into English. Vernier caliper in French "Pied à Coulisse", direct translation "Sliding "Foot".

There is a very good dictionary written by Henri Goursau "Dictionnaire de l'aéronautique et de l'espace" (Dictionary of Aeronautics and Space Technology) which covers pretty much everything you will ever need including tooling, machine tools, parts etc. that you would not normally find in a normal dictionary.
When I first moved here to France I would have been lost without it, in Belgium, generally most aircraft parts are referred to in English, here everything is translated into French, it took me a couple of months to get used to it, not to mention the differences between Belgian French and SW France French!
I could go on forever with all of this but I won't!

donc, bon journée Jean :)

A+

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bwolfie

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Oh no a French lesson, suddenly I am having flash backs to sophmore year high school!!
 
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Many engine and cycle parts even in english had their origin in french because that was the hotbed of technology for the era. The term "T de fourche" was a bicycle term where the stem forged or assembled (no welding back then) ressembled the letter T. In french it is still called that even if it doesn't look like a T anymore.

Back to the topic. I searched my parts catalogues and found the Atlas part number to be 030026, the early Commando part number is 060344 so it would appear the two are different. I then called my friend who has worked on Nortons for the last 40+ years and he said they were the same, with the same offset but maybe the difference was with the fork stops or headlight shrouds mountings. I can't see why a conservative company like Norton would have made different triple trees yet kept the same engine (all the way down to the points and tach drive) and transmission for a "new" bike unless they were forced to do it.

Jean
 
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Thanks for the research Jean, As my frame (50 Model 50) has bolt on stops I guess I'll see what I can find, I only really need the bottom yoke as the upper alloy yokes are pretty cheap new.

Webby
 
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I have an NOS Commando crown and stem laying about(yoke or trees or whatever), it has part# 061133. It looks identical to old Atlas/Dommi parts I have except it does not have the little hole drilled and tapped in the bottom for a steering damper anchor bolt.

Same casting number as Domi but the casting appears a bit thinner and lighter in places like they cleaned up the casting pattern maybe. Spacing on it between the fork tubes and stem looks the same as an Atlas. It is painted silver.

In the parts books for Dominators and Hybrids they call it a crown and stem or a crown and column and the top "tree" is always called a Head Clip, in the late Commando parts book I have they call them upper and lower yokes. I don't have a pre-73 Commando parts book though.

I know that when the 850 came out that they tweaked the steering angle a bit and came out with a new set of "yokes", they would have to if they wanted to keep the TRAIL of the front forks ahead of the tire patch where it should be. Mixing up 850 and 750 Commando yokes can lead to too little or too much trail making things either dangerous or slow.

So the 850 vs. 750 Commando difference is where the stories about different offsets come from. I think the 1972 and earlier Commando fork yokes have the same critical dimensions as Dominators can be swapped. I think it was for 1971 that the Commando got the yokes with a cleaned up more modern look.

Before I swapped front fork parts for ones from a different year Norton I would make sure and do a lot of research to make sure I was not doing anything dangerous.

Before I bought a set of yokes from RGM I would talk to them and clear a few things up. When they call one set of yokes "featherbed offset" and another set "Commando offset", they may just be saying that one set will work with all pre-850cc Norton frames and the other set is for the later 850 framed bikes. Again making certain mistakes with this could see you in a tank slapper at high speed, or dead.

Yes the pre-64 bikes had the 7" stanchion centers. This will not take quite as wide a tire as the later 7 3/8" jobs, but for anything but top-level racing this will not matter. The 7" jobs are cleaner looking because they don't have the hole for the lock cylinder in them.



I dont' need this Commando part and will probably get rid of it soon.
 
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Thanks for the info BenG,
The more research I do, the more I think that both you and Jean are correct. But one question, how is the offset measured ? From the stem hole centre to the fork stanchion hole centers ?
If you're interested in getting rid of your set of Dommie/Altlas/Early Commando yokes, I'd be very interested. :)

Thanks again

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