Having had a nice chat with Mike from Lotusbits at the NEC show, and heard the price of the lovely shiny aluminium expansion tank he'd bought along, I decided to fix the old one!
First job, wire brush in a drill to take off the paint and clean up the metal in the location where the brown streak originated. This showed not one, but three small craters:
Not having any brazing or welding equipment - or indeed skills - my plan was to fill the craters with solder, then file / wire brush to a tidy finish afterwards. I heated up the metal nicely with a blowtorch, but the solder didn't want to take in the holes. Still, it was willing enough to adhere to the clean metal around the holes, so the plan morphed to a less elegant solution where a blob of solder would sit over the holes. This seemed to work OK:
I thought it was worth testing this, so I stuck it in a sink full of water, covered the large pipe with my hand, and used a bicycle pump with a conical nozzle to put a little pressure into the tank:
This confirmed that, indeed, I had failed to seal the hole. So I had another shot, and this time it was more successful. It also identified that the rear cap was leaking, so a new one of those is on order.
A quick wire brush to smooth it down a little, then a coating of Hammerite on the affected area (which had already been used to repaint the whole unit when I did the engine rebuild 4 years ago). Doesn't look perfect, but it's black so it doesn't show up! Back in the car, and my cheap repair is ready to go... or at least it will be when the new cap turns up.
Worth trying to fix it before shelling out that sort of cash..
) on the carburettor of my Calivalier Sports Hatch, a round 1cm disc disc had fallen off permanently allowing more air into the carb by by a valve type thing.