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Hi Bastiaan. It can't be remain from earlier design then. I have 2 frames with the holes. One is 1938 for sure, the other is most likely 1938. It would be interesting to know the function of these holes. Thread is 5/16 BSC
Kalle, why can't it still be a remain from earlier design, than?
Most 30's models had this type of design, and again, in earlier models it was used for taking up the saddle springs and/or the rearcarrier.
In the M type these threaded holes had no use as they had seperate lugs for the saddle springs.
Also convinced it is a solid/one piece connection, most likely from a lathe, and it should be straight as I have never seen a curved one.
Maybe other members with some knowledge of the earlier prewar models can give their views, please.
Hi Michiel. Of course it can. But why to delete this part from some 37 models and then put back for next year. I agree with you that it should be straight. Very easy to bend it when rear frame is loose as this part only connects two sides of the rear frame.
One more quess is fixing point for high level exhaust.
Hi Kalle, yes, sorry, your correct, it could have another reason which we don't know (yet).
I looked in the 1939 catalogue and to my surprise all the 3 versions seems to be illustrated.
M20 standard : nothing to see, so probably a tube like the later models.
M20/M21 deLuxe, M23, M24 : ball with threads like your frame.
M22 : ball but without threads, like Klaus his frame.
I don't know....the high exhaust seems to be fitted to the saddle spring framelug, and the saddle spring itself seems to block fitment of a rearcarrier...
Klaus, just noticed the 1939 M22 rearframe is exactly as yours, it looks to have the balls without the threads and also the straight pillion footrests.
In 1939 the M22 still had 2 triangular toolboxes on both sides, placed high and vertical up the mudguard; on the other M models the single toolbox came between the chainstays in the position we all know and this needed a change in footrestlugs.
Hi I have complete "37" M20. That is an early "37" rear frame section. Based on that frame number, front part of the frame is from "late 38-39" m20. My "37" does not have the threaded holes. There were at least three variants of m20 made in 1937 with slightly different engine and frame parts. I have seen parts from the other two variants. Charlie
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Klaus, looking at the drawing and noticing more variants than I thought, I am not so sure anymore that in your frame the connection needs to be straight instead of curved like it is.. :relieved: :innocent:
Michiel, 1939 M22 you posted was just repainted and restamped KJM22 that was left over from 1938 model row. Later they produced small number of real KM22's with new 1939 engine and frame design. I have seen at least one KM22 stamped engine.
This forum is really great with lots of knowledge and information. I think we can assume that this type of frame was built until 1938. Except for the M24 which had no sidecar connections and frames made of Reynolds tubing.
It's amazing what details come to light.
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Thanks for all the info in this thread. I have front frame HM2398 on the bike I am building up with the later rear end.
Now I have to find a new rear end. The hunt goes on. Not too many early model M20s here that I have seen.
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How is the front end of the rear frame designed to take 39 wider engine? Is it a hybrid from the both types?