Re: welding alloy cylinder fin help?
The cylinder head fin repair is done.
This is the first time I have repaired a broken fin and here is how we did it.
The original broken fin was long gone, so I tried a donor fin from a trashed Triumph cylinder barrel, but it had iron in it (magnetic) and will not weld to aluminum alloy. So I picked up a broken BSA A65 head for $20 on e-bay and snapped off a donor fin.
Before
organ, errrr, fin donor
Using a cardboard template as a guide, I shaped the donor fin to the approximate size, though a bit oversized so the excess will be ground off once affixed to the cylinder.
Both the donor fin and the broken cylinder fin edges were beveled with a grinder, bead blasted and cleaned with a stainless brush and acetone. My welder Pat and I used scraps and clamps to position the fin and he ground out a little channel on the top scrap corresponding with the joint so that the weld bead went completely through the top fin.
Pat worked his magic with his TIG welder and 4043 aluminum rod. We also welded a 4” hairline crack in my inner primary cover.
Immediately after welding, the cylinder head was wrapped in insulation and let sit over night to cool down slowly, avoiding thermal shock and any possible cracks or breaks. Once cooled, the excess weld was ground off and then hand sanded.
I will bead blast the joint to give it some texture like the original sandcast. Vapor blasting will give the repaired area a uniform finish. The repair looks very good, but not perfect for the donor fin differs slightly in thickness from the original, but finding a donor Gold Star fin is not possible.
The patient is recovering nicely.
