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tobeesaWed Jul-05-06 10:49 AM
Member since Mar 18th 2009
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"1971 commando frame (what years will work on 20m3s engines)"


  

          

Does anyone know if commando swingarms will fit any year engine cradle(1971 engine cradle work on say a 1972-73-74-75 swing arm)vice-a-versa.I have a 1971 750 commando bolted to a transmission.No swingarm,no frame,I may buy a frame,and swingarm,on ebay,but dont know if different years will interchange with each other.Please help

  

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Rich PWed Jul-05-06 03:40 PM
Member since Mar 18th 2009
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#1. "RE: 1971 commando frame (what years will work on 2..."
In response to Reply # 0


  

          

Any of the drum-braked rear wheel swing-arms can be used (you don't want Mk111 850 which had a disc at the back)

The 750 swinging arm just had a single cross tube behind the pivot, that from the 850 also had triangular bracing plates supporting the tube so it should be stiffer. I have fitted an 850 unit in my Jan. 1972 750 (not a 20M3S motor but that doesn't make any difference).

You can use any frame if you are not worried about originality but 1972 onwards had improved stand fittings and parts are generally easier to find. The important thing is that 750 frames should be used with 750 clamps. 850 clamps had "ANG" cast underneath. Again avoid 850 mk111 (different instrument mounts).

Only you can decide if it's really cost effective. It probably isn't unless you know of a source of second hand parts. On the other hand, if you like swap-meets, it's great fun and the parts are out there !

  

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MichaelBFri Jul-07-06 09:07 AM
Member since Mar 18th 2009
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#2. "RE: 1971 commando frame (what years will work on 2..."
In response to Reply # 1
Fri Jul-07-06 09:08 AM by MichaelB

  

          

I don't know how much of the original bike you have. The 68-70 bikes used different triple trees and oil tanks. I am not sure how well these parts will interface with the 71 parts. The 71, 72, 73 750 frames are the same except for the side stand lug on the 71. The 71 is weak and is mounted to the inside of the frame loop. This needs to be corrected to the 72/73 style.
The 73, 74 850 frames are the same but as mentioned above need to be matched to the correct ANG triple trees. The 75 850 frame can also be used, just has an extra plate for the hinged seat. The old style seat will still work.

As Rich P mentioned above, the real issue is the 75 cradle and swing arm. The cradle has a non adjustable trans mount and the swing arm is for a disc brake. The swing arm will interchange with earlier cradles if you want to run a disc. Then there is the linkage issue.

If it were me I'd be looking for a 71, 72 or 73 750 frame with 750 triple trees. The 71 will need the side stand corrected and the 73 would have to be a 750, not an 850 frame. To keep it simple, focus on a 72. I would also try to score 73/74 850 swing arm, but the earlier ones would work. The 850 is heavier braced, but condition and price would dictate which one. Most used ones are tweaked.

Mike

  

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