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Rusty motorcycle gas tank, sealer failed

I have a nearly antique BMW R-80 that had a leak in one of the bottom seams of the tank. I got some sloshing sealer that is used by airplane companies to seal tanks on brand new planes as they are built. Should be good stuff, right? Weellll airplane fuel doesn’t have any ethanol in it. It is nearly impossible to buy auto fuel without 10 to 15% ethanol around here. I was not aware that the ethanol fuel would “eat” the sealer. SOOOO, now I have a tank with a thin film of worthless goo on the inside.

I did an internet search for info about POR-15, which has been discussed here many times. I don’t think this exact issue has been addressed though. The person I contacted said the company makes something to clean out the “failed sealer”. Then there is a process to go through to get rid of any remaining rust, and finally reseal the tank with a compound that they say is impervious to ethanol fuels.

Has anyone here had this sort of situation? Did the POR-15 product fix it? If not, what did you use?

Tanks, I mean thanks.

MG

If you’re not on a tight budget I’d find a motorcycle restoration shop that could take care of this. You don’t want to compound the problem.

My guess is that a motorcycle resto shop would do the same thing I will, IF the POR-15 chemicals will work. I just need a recommendation or a warm fuzzy feeling before I start. It’s $48 for the kit. That’s not exactly cheap. So far I’ve dumped $300 in the last month, and I have yet to ride it this summer. An Apple Hydraulics rebuilt master cylinder is the next thing after the tank, but I want to be sure it runs, before I have make it stop.

I didn’t bother looking at the name - you’re plenty knowledgeable. But how many folks will have faced this problem? Not many. Maybe post this on a bike forum?

All I can say is that about 8 years ago, I used the POR tank sealer on an old 75 Jawa CZ250 that had rusted pretty bad and was clogging fuel filters. No problems afterward but it did not leak prior to the application. POR has always stood behind their products for me even sending me samples at times. They claim it will be OK if you follow their instructions on prep (especially removing the failed stuff) so I would be comfortable using it. They’d probably do something to help if it failed for some reason as well…

Did you mention the seam leak to them? Were they OK with it bridging that leak?

Seam is on bottom of tank so you might be able to weld shut and not affect visible paint??

It is rusted in the seam which appears to be crimped together and welded. There is also some rust visible through the tank filler, but that’s not leaking, yet.

I’d bring it to a radiator shop and have them fix it. I’ve done this several times to radiators and gas tanks to vintage cars. It’ll be good as new and pressure tested when you get it back so you won’t ever need to worry about it.

Since the tank is now full of goo and rust, maybe it would be better to locate a serviceable used tank for this bike…

That would be best but could be trick, it being a fairly vintage bike.
I suspect there aren’t too many part bikes like that around in this country.

R60, R75, R80, R90 Beemers were fairly common, made for many years and they all share the same basic gas tanks. Optional high-volume tanks were available for them in the aftermarket so I suspect there are replacement tanks available…Like anything BMW, it’s just a matter of money and how badly you want it…

Lol - true.
I’ll ask a friend of mine. He’s restoring a vintage BWM. He may know of a good parts source.

I have seen used BMW tanks on ebay with starting prices in the $500 range. No thanks. Buying one of them might not cure the situation as it could be more rusty than the one I have. I’d rather fix the devil I know, if pssible, than to buy more problems. I just don’t know if POR’s solution will do it. The maker of the “goo” I have is no help.

Gotcha.
Seriously, in that case, I’d see if you can find a radiator shop in your area. My old rambler tank looked like the moon’s surface on the inside since it had been sitting without a cap on it since 76. I tried rattling it out with a chain to no avail. It also had a leak. A replacement tank was cost prohibitive in shipping alone so got it fixed.
After I got it back from the shop, it looked like new. It cost me just shy of $200.

I have seen used BMW tanks on ebay with starting prices in the $500 range. No thanks. Buying one of them might not cure the situation as it could be more rusty than the one I have. I’d rather fix the devil I know, if possible, than to buy more problems. I just don’t know if POR’s solution will do it. The maker of the “goo” I have is no help.

Remember, we’re talking about a motorcycle tank. Usually, a rad shop is going to be brute force and not worried about appearance. This thing has vintage paint I would assume MG would like to keep intact if at all possible. Repainting tanks is a PITA because they see gas spills all the time. Need hardener and have to match the rest of the aged bike paint. I’d use sealer first.

Did the chain trick on that old bike tank. Along with the metal cleaner and etch, it did a fair job of removing the loose scale. The sealer takes care of the rest.

Ah, yes you do have a good point there, Turbo. Car tanks are of course hidden where bike tanks aren’t.

This is just one of many…Stop working on junk…

The Cafe Racers I know cut out the rusted metal from their gas tanks and then weld in a formed pieces of new metal.

Tester

I’m admittedly not a motorcyclist (I like bikes but just never got the liscense), but because we’re talking about gasoline I’d recommend either going to a pro to get it sealed properly or replacing it. Gas fumes are IMHO too volatile and the risk too great to be fooling with a rusted out tank.

If the seam is in a spot that’s not too noticeable, how about using some JB Weld or epoxy putty? It can be ground and painted after curing.