Sat down to dismantle Puch Magnum and found one small hole (quickly followed by two more!) in the tank where the Magnum seat touches. Seems this is the same place I noted rust on other Magnum tanks. Checked my spare tank, and, sure enough, it had holes there too! BIG ONES! (So much for the simple replacement solution.)

The original tank was Kreemed by previous owner and is in otherwise decent shape. I know a lot of guys swear by JB Weld (I have never used it). I learned it is, in fact, an epoxy. How large a hole can it repair? Should I grind all the rust down first, even though this will likely create more and bigger holes? Can I use regular two part epoxy and some fiberglass surfboard mesh? Would it be better to do this on the outside and THEN use POR15 or some other tank sealer on the inside portion? I know this topic has been discussed, but I am looking for an answer about the BEST way, especially when the larger holes on the second tank are about 1/2-5/8" in diameter. (I would like to experiment on that one first).


I discovered a hole in my tank while kreem C'ing. Sucked hard...JB weld did great...the hole was about 1mm could probably get away with using it on a 2mm diameter hole but thats about it....


epoxy is ok..JBWeld is a metal-filled epoxy.

i asked a supplier about building a fiberglass tank.. they sell a special eopxy (cant use polyeter) .. expensive as hell..

the best way, imo, is to soft solder it, like they used to do with automobile dent repair before Bondo (beware.. Bondo is polyester) came along.

My tank has a couple large holes and weak surrounding areas due to being badly rusted. The previous owner was kind enough to patch them with sheet metal and solder .. and it was Kreemed. The patched areas will likely outlast the rest of the tank.

caution .. spark/open flames + gasoline fumes = trouble.. If you don't know how to work on fuel tanks, learn or forget it..


You will cgase your rear end around in circles. I would suggest getting a new one.


silverfox...nah i disagree with can definitely soft solder it, or maybe even brass weld it....


Don't use JB for anything more than pinholes. I know firsthand it won't hold for more than a week on the larger stuff.

I would suggest patching the holes then sealing the inside with POR15.


If your going to be able to see the patch outside anyway,then wash out the tank good with Superclean and water,let it dry,and have sheetmetal welded over the holes.Then fill the tank with muriatic acid(but only if you are an adult and know how to use it properly)let it soak overnight,rinse it out good with water,then fill it up with one quart cheap 4-atroke oil,and kerosene.leave it overnight again.Then check for leaks.If there aren't any,then pour out the kerosene and oil,the oil coating left on the inside of the tank will prevent it from rusting.When you are ready to use it,just fill it with premix.What little 4-stroke oil and kerosene that might be left in there won't hurt anything.I do not recommend Kreem at all.It will not seal large holes,and it will eventually come loose,then there is no way to repair the tank.


Brian Mikami /

The Magnum tank I painted for the Puch80 project had pin holes...Smitty used JB weld on the outside, and Por15 on the insides...hope it works.

If you can sheetmetal and braze a patch, do that. Fiberglass cloth and epoxy resin on a well scuffed tank works too. But the inside will have to be sealed with Por15 or (what's wrong with it? ) Kreem...I thought that stuff was poured in and sealed the entire tank...gotta be a good thing eh? Good luck.


I don't know what Por15 is,but have seen several motorcycle tanks that were coated with Kreem,where the Kreem started to peel off,and since it's inside the tank,theres no way to get to it.True enough,it could have been done wrong in the first place,but that is another problem with it.Even if you follow the instructions to the letter,it's hard to know that it was done right or not.If you miss just one spot,inside the tank,where you can't see it,it will eventually start to peel around the edges,gas will get between it and the tank,and then it will start coming loose all over the place.Jerry.


Well, I ran around yesterday, checking out various JB Weld-like epoxy putties from auto supply stores and, as feared, all recommended not using on holes larger than 1/4" (pretty much as respondents above have suggested. The idea of brazing was mentioned by one auto guy, though I have never done that before. I do recall someone years ago mentioning that they had done it to repair an unsightly ding in his Magnum tank. I think he used a quarter.

Anyhow, I poked around the really bad tank and, yup, those holes are larger than the 1/4" diameter. A couple are larger than 1/2" for sure. The other tank has some pinholes, as mentioned where the seat meets the tank, and it wouldn't be a problem visually since you can't see it when the seat is on anyway. I am hesitant to grind those holes more to see what might happen.

I had another idea though it might not fly either: What if I used an inexpensive funnel and mixed epoxy and slid it down to that part of the tank, angling it so JUST that inside wall was "rebuilt" from the inside? Sure, my tank capacity would be a LITTLE smaller, but then perhaps I could grind down the outside without fear that I would totally destroy the tank. What do you think?


i have a magnum tank but its got some rust inside but i can be kremed

if intereted 50.00 shipped (neg)


The thing about epoxies is they do not really adhere well to anything except epoxy .. they will stick to metal mostly because the surface is very clean and is completely roughed up with something like very rough sandpaper... the "tooth" makes it stick.

A putty compound should stay in place if you can mold it into the hole and mushroom it out on both sides .. i've used epoxy putty for various things from case repair to tank repair and have a lot of faith in it if it's applied properly.

But it's a plastic.. and the tank is metal .. any joining will be a relatively weak bond.

Your plan sounds ok except that the inside surface of the tank is unlikely to be clean. Maybe back it up on the outside with some glass cloth .. If it don't work the cost of experimenting was minimal.

Brazing is kinda tricky .. and requires very high heat. For safety sake, a pro would probably want to pre-bake the tank in an oven to evaporate all gasoline in the pores of the metal as in welding..

If cost were no object and saving the tank was required, i might get a quart (actually a pound.. sold by weight) of 2-part liquid urethane (Devcon Flexane or similar) and coat the entire inside of the tank with a thick rubber coating..


Is the part of the tank where the holes are fairly flat,or is it curved?


In response to Jerry, immediately above, the holes are on the lower end of the Magnum tank, and, if you were to look at one of the bikes in the photo section, exactly where the Magnum seat abuts the tank. In other words, it is not visible unless you remove the seat. That tank area is (mostly) flat. One tank (the worse one) has holes at the very bottom where the seam is; the other has rust pinholes 1 1/2-2" higher up and more centered, but still behind the seat abutment. I hope that makes it clearer.

I am still hunting for the "best" even if not "perfect" solution, or, at least one I can handle without too much money or hassle. Yesterday's hunt took me to a marine solution. One of my folks' neighbors is a sometime deep-sea fisherman, boat owner/operator, auto/moped/go-cart mechanic, and his statement was that all the boat gas tanks he has seem repaired (up to 80 gallons) were done with boat epoxy. He suggested three pieces of fiberglass, each in increasing size over the holes, followed by epoxy resin. He insisted that he has never seen one fail yet. I think it was joew who said might as well give it a shot, not much to lose. So I think that might be the first step, unless my other internet hunts come up with better solutions. We'll see...Keep the opinions coming, if you like. I am always hunting...thanks for input.


due to the nature of iron rust, it must be completely removed or sealed against moisture and air (oxygen).. or it will spread.

Unlike aluminum or zinc rust (oxide), iron rust is flakey and only loosely attached to the underlying metal. If it has access to any air and water it grows in an electrochemical reaction. As it grows it will break through a thin, brittle coating like paint. More air and water gets into the microscopic paint cracks and growth accelerates.

The point is that if you manage to repair or coat the inside or outside of the tank, wherever holes are rusted through will need proper treatment on both sides. Otherwise the repair will be undermined with growing rust..

the epoxy/glass thing sounds good... only drawback i see is cosmetic treatment... lots of hits about epoxy repairs like THIS one.

_most convenient material to use on a patch is the epoxy which comes in two connected tubes. A couple of ounces costs about $2.50_

I'm almost inspired to try building a fiberglass tank .. one of my bikes has no tank.


I was just thinking that if it was fairly flat,you could grind all the paint off the area,and have a piece,or pieces of sheet metal welded over the whole area.The welds shouldn't leak.I have seen entire gas tanks made out of welded together pieces of sheet metal.If it's a fairly large area,it's even possible to cut out the whole section,and have a piece of sheet metal shaped and welded in to replace it with,that way you wouldn't have rusty metal on the other side of the patch that would eventually rust through again.It's even possible to grind down the welds,and finish it off so well,you can't tell it's ever been repaired.I've seen antique motorcycle tanks done this way,where it simply wasn't possible to get another tank.Its not cheap though.If looks are really important,you might want to try and locate another tank.


hi; there an old school material called marine tex. i patched a half inch hole in a cushman float bowel about 12 years ago,and its still holding. it can do anything. you can patch a hole in a sinking boat with it. not kiddin.


Research continues: Discovered that we have a rep for POR15 in Honolulu, a crusty retired auto mechanic who sells it for supplemental income and to write off his house. Finally got to speak with him, told him the problem and he said flat out that what I was suggesting should work just fine and they had used it on tanks before. He said if you wanted to do it with metal, he recommended soldering (with a soldering gun, not PROPANE torch!) a piece of copper plating over the hole. He was on his way to do his Las Vegas donation so he told me to come on out to his house after Oct. 1 and he' d take a look at the tanks and make suggestions. Even said he had some copper around.

So...we shall wait a spell, continue research and see what happens. Perhaps, if anything, we'll all learn MORE than one way to handle the problem (with no explosive casualties). Thanks to everyone so far (for real answers, not smart-ass commentary).

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