Vic;

I went through what I had in my archive, and the consensus appears to be in favor of a product like Gas Tank Renu professionally applied.  (See posts below by Jan and Bob Douglas).  While POR 15 and others also have products, this is the only process I have heard of where it is triple baked.  The process appears to be franchised in several areas of the US (and may be available "down under" as well).  Go to
http://www.gas-tank.com to read about it.  Jan also recommends "a red product approved by BMW" that sounds like Renu.

Ron Tebo

... The only way to restore the tank is to take it to a metal cleaning shop where they can clean rusted metal.  It will also remove all paint and crud at the bottom.  The cost is about $50-$75 for a gas tank.  The next step is to a radiator/gas tank repair shop ... they solder metal patches over the pinholes (mine had quite a few) and seal the tank with a tank sealer mixture (cost me about $150).

Many US radiator/tank shops will both clean and repair.  I had my S.II tank done around 18 months ago for about $100 which included boiling, patching, sealing, and paint(exterior only this time).  Once cleaned, I was surprised at the large number of pin holes they found.  I think the shop was too, and probably would have priced it $20 to $40 higher if they had realized how bad it was.  I expect the going rate to still be in the $120 to $160 range in the SW US.  Material cost to etch, seal, and paint the tank myself would have been about $50; likely more because I probably would have still had to have the "crud" boiled out at the shop.  You can buy the DIY kits from Eastwood, J.C. Whitney, or half a dozen other sources.

One recommendation on the sealer is to ask for the alcohol resistant version.  It is white rather than the yellow that's more commonly used.  It's slightly more expensive, but could save you some trouble from alcohol fuel mixes or additives down the road.  A bit paranoid maybe, but figure it's a tough call on what will be available at the pump 10+ years down the road in different parts of the country.

I had the yellow stuff put in mine because that's all the shops in my area were offering at the time.  Today I'd probably opt to have the shop boil and patch the tank then install the white sealer myself if all they offered was the yellow variety.

Regards,  Bob Douglas

Whatever you do, don't do the franchise deal.  They will tear your tank up.  Boil (radiator shop) paint or powder coat and coat the inside with any good gas tank sealer.  There are plenty of them out there.  I use POR 15 and have done 5 sets now and none have come back.

Paul

If you guys have a single tank or the later dual tanks, it may not be cost effective to do it yourself.  Here are the facts:
Restorers in Ohio have their fuel tanks dipped at our metal cleaning facility in Cincy.  They are returned completely free of paint & rust (you want it rust free to see any pin holes that need repair).  One local radiator & tank repair shop, that servers a lot of us here in Dayton, will not let you bring in a fuel tank into his shop, unless it HAS been dipped.
I coat my tanks myself now because my volume is getting higher.  I use "Fuel Tank Liner" manufactured by Damon Industries and I start with 3-quarts (approx. $60) so that I have more than enough to slosh around.  I coat all the tanks as a batch because the liner will go bad after a short time (dries up in the can after it's opened).  Follow their directions.  This is what the Pros use around here, and all the tanks repair shops here in the "Birth Place of Aviation" Dayton, OH.

Jan Servaites

Here are some more comments on Red Kote fuel tank liner from Damon Industries:
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