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Mk Frame repairs

Started by giz.neal, 03 Nov 2017 at 14:22

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giz.neal

Do any members have tips on repairs to early Mk frames (T35 / Mk 3). In particular the rear downtube in the area of the 'slash' cut above the rear fork/footrest/gearbox lug?

Any help appreciated

Steve

eddie

Steve,
          I guess that the tube has cracked tight up to the lug - in which case, a repair that I found to be successful was:- cut back the end of the lug by about 1/4" to leave the stub end of tube showing. Carefully file away ALL traces of braze from the area around the crack (this is to prevent brass inclusion in the new weld). 'V' out the crack to about 1/2 depth, then get the crack TIG welded. Finally, get the area built up with silicon bronze to restore the original length of the lug (purely cosmetic).
  Before fully reassembling the bike, knock the core plugs out of the inside of the swinging arm pivots. You will then see that the swinging arm pins are hollow - turn up a tight fitting plugs for the pins and press them in - then refit the core plugs. The grease will then have to go through the holes into the bush rather than just pushing it's way out and past the core plug. On Mark machines, the area around the swinging arm pivot is subject to some complex stresses that can cause these cracks - especially if the swinging arm lubrication has been somewhat lacking.
  Good luck with the repair,
       Regards,
                     Eddie.

giz.neal

Thanks Eddie, excellent advice as always!

Steve