frame swap

Does anyone have experence doing a complete frame swap from a 1968 frame to a 1975 frame. I am trying to come up with a list of issues I will have to deal with. I know their are differences in the frame, iso's, steering and mounts. Will the forks and trees swap right over. I want to see how difficult this will be before I commit to a 75 frame purchase. Or just keep lookin for the proper 68-69 frame. Mine is orig unmodified frame, unsafe..
Thanks,
Dan

hey ddoyle, what actually is unsafe on your original unmodified frame??

The very earliest Commando frame design had no bracing tube running below the main spine tube.
As a result, many of those early frames broke quite quickly around the area of the headstock (main spine tube and both down tubes can break) , so they were normally replaced under warranty with the modified frame.

ddoyle said:

I know their are differences in the frame, iso's, steering and mounts. Will the forks and trees swap right over.

Click to expand...

Theoretically, you need to use the 850 ("ANG" marked) trees/yokes with any 850 frame, due to the differences between the 750 and 850 steering angle.

The coil mounting brackets are different, and the head steady mounting could be different, although I'm not totally sure about that.

The 850 frame has no cross tube below the gearbox with the mounting brackets for the main stand. There is a cross tube on the '71-on frames but it's positioned further forward, as those later Commandos had the stronger main stand that fitted onto the engine cradle. The side stand and mounting is different.

According to the frame information given on the atlanticgreen website the late models could have wider frame seat loops, so the Fastback style tail section may not easily fit the later frame loop?: http://atlanticgreen.com/commandoframes.htm

I had occasion to fit a later set of triple clamps onto an earlier frame and had to have the steering head bearing recesses deepened at the bottom to accomodate. I would therefore imagine that if you wanted to keep the original clamps you would have to make up a spacer to maintain the correct distance, as L.A.B. says you should consider changing the clamps depending on whether you get a 750 or 850 replacement frame. Also the steering stops are different on the later frame and consist of a single centrally located tang as opposed to the pair attached near to the bottom of the steering head on the earlier frame. The tab that engages the anti theft lock on the earlier bike is replaced by a plate that is broader on the newer model. The earlier models have tangs fitted on the rear loop and main frame plate to accomodate a tire pump. The isolastics themselves will fit either frame, although I would be inclined to fit the later type if I was doing a frame swap. L.A.B. is spot on (as usual) about the other differences. There are a couple of early model frames on e-bay at the moment including one in E-bay stores the last time I looked.

Keep the old frame. In a few years there will be none of those around.

Thank you all for the replies. Looks like I will be waiting awhile then. For fun you can still see the recall info, go to NHTSA, ID number 74v23000 for a good read. What are " unusual conditions of use", and I like "induced weakness innitiated by unsatisfactory crating and warehousing procedures"

Dan