Norton frames

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Against the advice of wiser folk, I have decided to build a 750 from parts as a weekend canyon rider and occasional vintage track day bike. I am having difficulty in selecting and locating a frame. My preference is to build a ’73 750. The ’73 frame for some reason seems to be in short supply and it seems that most ‘new’ frames are fabricated around the ’75 850 design. Will a ’74 or ’75 frame accept the ’73 750 motor, wheels [disk/drum], and triple tree which I already have restored and ready to go, without making any major modifications to the frame?

Thanks for any advice?
 

MichaelB

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The frames are the same. The differences are in the triple trees and the cradle /swingarm.
750 specs show a steeper rake than the 850, however the difference is in the triple trees, not the frame.
The 75 / Mark III has a different cradle for the Mark III drive train. It also has a reinforced swing arm. An earlier cradle will fit the Mark III frame and either swing arm will fit the earlier cradle.
The only real issue is you will need a non Mark III cradle to fit your drive train.

Correction: I just checked current stock numbers with Andover / Norton and Norvil and found the Mark III and Mark IIa frame have a different stock number than the rest. I don't know what the differences are and will have to differ to someone else. Sorry.
 

Ron L

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If memory serves me right, the difference in 850 e-start and non-e-start frames is the gussets where the hinged seat mounts. You can use a non-e-start engine/trans and all the body parts on an e-start frame. However, if you use a non-e-start frame with and e-start seat, you don't have the gusset and hole for the seat lock.
As to the 750 vs 850, the steering head is raked out (I believe two degrees?) on the 850 frame, but the triple tree stem is angled to give the same wheelbase. In other words, use 850 trees with an 850 frame, 750 trees with a 750 frame to retain the same geometry. Mix and match and you may or may not see a slight difference in handling.

Ron L
 
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Thanks for the great info. I probably would not have found out about the triple tree until I got the bike together and measured for spec. As luck would have it, I found a great '72 frame two days after my original posting. I hope to have a runner in time for fall rides in the blue ridge. I will keep the information though. I have the 'build it' bug as bad as I have the 'ride it' bug.
 
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The 72 frame should serve you well. We always put longer gussets in the inside of the top shock mount to better support the rear loop. Just make it follow the piece already there but make it at least an inch and one half longer then weld over the old one with MIG for it's low heat. This loop is most always bent down from years of use and should be straightened before gussets or powder coating or painting is done. To me the best thing about a 72 frame is that the rear body work for a Fastback will still fit on these. The rear loop on later bikes is a half inch too wide. Also the 71 frame has that nasty side stand mount. norbsa If you like to read the timing on this couldn't be better .http://www.vintagenet.com/phantom/wsc.html
 

Ron L

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>....>snip<.....To me the best thing about a 72 frame is that the rear >body work for a Fastback will still fit on these. The rear loop on later >bikes is a half inch too wide.....

I have heard this from several different people, including dynodave. I'm not sure this true. These bikes are thirty years old and the rear loop took a beating. Maybe they have just been bent and straightened, or maybe it was just bad quality control.

My '75 MkIII has worn a new old stock '70 fastback tailpiece for the last 10 years. I recently checked it on the other frames in my shop. Two '74's and two '73's. It fits all of them perfectly, just like my two '68/'69 tailsections. Coincidentally all the tailsections fit the '69 frames also.

Ron L
 
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rear hoop

We checked Three frames from 72 and back and 3 from 73, 74. the difference was about one half inch wider on the later models. We were checking about sixteen inches back from the maim cross bar cause this is were the tightness is. There was a stamped number on the frame of these later bikes so I am thinking that these were the Itailian made. You might check your frame for stamped numbers if it has none this problem of a too wide could be Itailian. norbsa
 
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Thanks Dave, I am fighting with this right now trying to find a good way to bend this back to a norrower loop without distroying the fresh powder coat. So far Iam looking for some two inch channel iron that could be rubber lined and clearance drilled for half inch running rod above and below the tubing. this would be used to crush the rear loop to the just the little bit I need. Ever tried any thing like this? I am determined to get this to work and never thought to check the fit out before getting this far. norbsa
 
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