P11 neck bearings, what to do?

Old Brit bike frames are hearth brazed, as this is the only real way for the brass to fully wick into most of the joint area. Some lugs are retained on the frame tubes by nails driven through pre drilled holes to keep them in position during the joining process. Any form of welding in or around a brazed lug joint can compromise the joint strength, and as such its always a good idea to TIG braze if this seems feasible.
 
Carbonfibre said:
Old Brit bike frames are hearth brazed, as this is the only real way for the brass to fully wick into most of the joint area. Some lugs are retained on the frame tubes by nails driven through pre drilled holes to keep them in position during the joining process. Any form of welding in or around a brazed lug joint can compromise the joint strength, and as such its always a good idea to TIG braze if this seems feasible.
I have never TIG brazed but have Oxy-Acetylene brazed with good results, just never had to do it on a bike frame as all my frames with the exception of this one are welded.
I usually do all my own welding, MIG, TIG, oxy-acetylene. I had a change of employment that has had a negative effect on the amount of after hours shop time that I have available to me. A trusted shop did the job with full understanding of the dangers involved. Possible problems with welding the casting were considered and precautions taken to insure that they would not arise. I am very satisfied with the results.

Will
 
There are no problems with welding investment cast lugs, as these are steel and present little difficulty. Only issue is the heat of the welding process is a great deal more then that of the melt temperature of the material used to make the frame, and even though all seems perfectly ok it is possible the brazed joints will have been weakened by the welding carried out.

If you are sleeving something like an investment cast headstock, to take different bearings, then TIG brazing is the best process to use, as this puts the least amount of heat into the job, and greatly reduces the chances of any problems with the original brazed joints.

An example of what can happen when welding is carried out adjacent to lug brazed joints, was a BSA MX frame which had had welding carried out near to the front motor mount, and which unfortunately resulted in the brazed joint failing after landing from a big jump (there was a picture of this on the net several years ago, but not sure its its still to be found).
 
Carbonfibre said:
....Only issue is the heat of the welding process is a great deal more then that of the melt temperature of the material used to make the frame, ....
willh said:
We took are time and kept the temps down.
All is well, for the most part the welds are far from the brazed areas and were welded in small doses and allowed to cool down in between to avoid the problems you speak off.
 
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