Repairing rusted headlight bucket with lead
Moto Guzzi V700, V7 Special, Ambassador, 850 GT, 850 GT California, Eldorado, and 850 California Police models
Thanks to Joe Tokarz for sending me this information via email. In Joe's own words and photos:
The back of the V-700 headlight bucket was full of small rusted through holes. It was caused by turning the bucket facing up to fit a large Vetter fairing. Although the bucket had a rubber cover it didn't keep out the water so over the next 40+ years the deep bucket collected water which caused the rusted through pin-holes.
To keep the bucket original I used lead instead of plastic filler figuring that leading was the better choice since it's less likely to work loose over time. I know a little bit about soldering but filling sheet metal holes with lead is different. Here's a tutorial from Eastwood.
I used a very old but working 100 watt soldering iron, small butane torch, soldering paste, lead free solder without flux core, and denatured alcohol for flux removal.
The rusted holes tend to develop a burr so lightly sand the surfaces until the holes are flush with the surface. This made some of the holes a bit larger.
When the iron was up to temperature with tinned tip, a thin coat of flux was applied to a small area to get the process started. Solder was applied between the bucket surface and the side of the tip slowly pushing a solder puddle across the holes. Lead has a high surface tension so bridging small holes is easy. I started with a small cluster of holes to get a feel for the puddling then worked over to the bigger holes.
When all the holes were filled the lead was uneven so I used a small butane torch and a wafting motion with just enough heat to flow and smooth out the high spots to reduce filing. Coarse and fine files smoothed and shaped the repair. A medium scuffing pad on the angle grinder flushed out the margin where lead meets the steel bucket.
After prep and paint its looks pretty good.