fin repairs

[limeyrob]

A fin was broken off my spare barrel and I have a horrible feeling it happened on the way home when I hit a pot hole. Anyway I also have a spare A7 ally head with a bit of fin missing and the 8" brake plate that needed the lug extending so last week I took the lot to a local welder.
Picked it all up today. Brake is a nice job, I made a bit of ally fin and that looks really neat, and best of all the CI fin is all welded on and nearly invisible.  Break line was about 5".
£100 all in which seems OK.  So if you do break a fin don't despair.  For anyone near Heathrow it was Sparks Welding, Colnebrook.

[Jules]

I have/had a broken fin on my barrell when the m/c shop that bored them out dropped them (after they had been bored!) and when I enquired of some good welders they were very reticent to weld or even braze it back on due to the possibility of creating bore distortion due to the very localised heating. They suggested that the whole barrell would need controlled heating, then controlled cooling, then the bore honed!!
I ended up having the fin just tack welded as a compromise, so far so good....

[limeyrob]

Yes, there seem to be two schools of thought:
1 heat it all up then weld with it very hot and let it cool very slowly so all the stresses relax and there's no residual stress.
2 Word in very short periods with the least heat possible from the centre out and aim to not trap any stresses as its cool between each weld.
Looking on youtube both seem to work for fin repairs. I think its a case of what ever the welder is comfortable with.