We found an old machine gear box which allows four different rotation speeds. We mounted it on a stand with washing machine motor one end and a large face plate the other. A few holes and four arms bolted where needed and ratchet strap and around it goes. We have it in a back room at the muffler shop and just let it run. I use a rubber plumbing cap and hose clamp to seal the fill hole. The fuel out tube and vent tube need to be sealed also. Failure to do so on my first tank left that very fine orange dust all over the place. In spite of my help building the rig Kevin still charges me for each tank he does. Seeing as the process lasts three days, moving the tank so all surfaces are cleaned takes three moves if not more. I'm concerned this tank may leak when done. 

I think the rocks and mud were added by kids some where along it's life. I agree everything I put in I account for and remove. I will take pictures and sooner or later learn to post here. Steve (CTR)

PS Kevin was telling me about a gas tank he cleaned. Ford PU old school. It would crank and run but die after a few min. Turns out some kids had put frogs in the tank and the skins were floating around finding their way over the pick up. 

I may have to try this soon...mine leaks.Thanks for sharing this.

Will most likely be trying this when I get around to putting my new engine in and redoing my dash for the coming season.

I like your tank tumbler idea!  I've used gravel from my driveway, shake-n-rinse, repeat.  But I usually take the gravel back out!

I have been seeing the large tanks suffering rust around the neck from the foam ring below the seal. I have yet to have to repair one. When fitting 5 gallon fuel cells I have used MGB filler necks to maintain normal fuel location. They are about 6/7 inches long and would make a good repair source. 

I'm currently working a mid 80s classic, having rebuilt the engine, tranny, suspension and brakes. I guess everything mechanical has been rebuilt or replaced. While leaning the tank to release the left upper shock pin the fuel line popped off the tank. I was glad I had removed the spare and boot carpet. It's fun trying to keep a finger over the fuel out and remove a large tank from the boot with 2/3 gallons. I have been involved with this car since early 2000. It was driven to high school by two brothers and then to college by one. It has been around my shop for 5 or more years. I have driven it many times and it has always given great MPG and would run 65/70 all day long. Once the tank was out I was surprised to hear something moving around in the tank. The fuel did not smell good so I poured it into a clear plastic container. To my surprise there was a hand full of large gravel and a inch or more of what looks like carolina red mud. I removed the sender and flushed the tank with hot soapy water. Once dried out I filled with rust solvo and will empty that and fill with rock polish medium and tumble in our tank cleaner. Rotate one way for 24 hours and then flip and run another day or so. A new sender and seal and it will go back in place.

I have several tanks around the shop that have been treated and lined and the coating is flaking inside. I'm sure they were not done correctly. Any ideas of how best to get that mess out? Steve (CTR)  

Yup Alex.... it seems we loose our fuel cap keys more often over here!  Most of the "banged up" is indeed caused by someone prying off a cap for which the key has been lost!

My Mini had a rusted filler neck that was the source of fuel fumes in the boot. The rust was caused by a foam plastic donut around the neck. I bought the POR-15 motorcycle repair kit, which includes some cloth gauze. I used the cloth and the 2-part POR-15 to seal and strengthen the neck, then did a full tank seal. Great stuff. The POR-15 looks like galvanized metal when cured and is paintable.

I've never had or seen a damaged filler neck - other than a tank which had had the locking cap prised off to steal fuel.

On the other hand, filler caps are now service items as the rubber seals go in next to no time.  The latest one leaked after 10 days...

Before doing anything drastic, check the condition and thickness of the cap seal.

Thanks Kevin!  Good info.... When I rebuilt my MK1 Cooper S, I happened to have a good fill neck I'd chopped off a rusty old tank.  I cut a banged-up one off my right hand tank, and oxy acetylene welded the replacement with the tanks completely out and clean.  That looks totally doable using the little fake neck as a donor.... but I bet it would be a pretty easy repair to do without removing the tank by simply epoxying the "fake" over a carefully cut off neck.   Is it "POR15" that is used to coat and seal up pitted tanks? 

Jemal, I did this on my RH tank a few years ago. I cut the neck and the fake so the join would be just below the rubber grommet.
After cutting the neck off I filled the tank with hot water, tipped it out, then filled with cold water up to the bottom of the neck.

I welded it with oxy acetylene and steel filler wire (I had no TIG welder then).

Filler cap fits fine.

Anyone else try this?  it's pretty common to find the fill neck of a classic Mini fuel tank banged up enough for fuel to run down the side when cornering.  Well, OK, that can happen anyway, but you can't buy a replacement neck... it's just part of the fuel tank.  

You can however, buy the fake little fuel cap to "S-iffy" any saloon with dual fill-necks, so in talking to a customer, I wondered how well made the little stub-necks might be, so I got one and made this short video...  It is steel and can be welded, but I bet it could be carefully epoxied over the neck with the damaged one cut off....