Background: My project bike, a '90 K75, is up and running. Minor issues that I'm working on. But the rattle-can spray job that I did on the tank while reasonably decent isn't quite as nice as I wished. So casting around for a solution, a friend showed me a tank he did by simply polishing the tank on a buffer. Now that looked very interesting. Several caveats, first I don't want to sacrifice my current tank in the process. First I thought to find/purchase a new tank. Greg doesn't have a proper one for this '90 bike, but thought that I might locate one for USD$100. So far no luck. Now I do have a tank off the parts bike he sold me but whoever rode it down obviously did a tank slapper. There are serious dings in the right rear of the tank and under the BMW logo on the right front. So my thought is to beat out the dings as best I can and then do the equivalent of "lead (ing)" of  the dings and then grinding/sanding/polishing the filler metal down. And in the process polish out the rest of the tank's upper half. The filler metal I am thinking to use is the Durafix-Aluminium-Welding-Rods-Brazing-Easy-Soldering-Low-Temp things your find on ebay and the internet. The tank itself is sound and doesn't need to be repaired just leaded and polished. For anyone not quite sure what is meant by "leading", you take a torch, heat a piece of metal usually a external car part and apply the metal lead to it. After the lead metal semi-melts onto the car piece rather like bondo you grind and polish off the excess. Way back when, this was the preferred method of fixing dings in cars or bikes.

My question is has anyone else ever tried anything similar and is there a difference in color between aluminium and these brazing/filler rods? Really don't want to do the work only to learn there is no way you can make the different materials blend into one another in terms of color. Appreciate any useful suggestions or experiences.
Thanks
J.

I don't know whether it would work on a tank but we have a couple of local shops doing vinyl wraps on motorcycles.
You would have to be extremely careful about not spilling fuel around the filler neck and the area around the neck would have to be painted.
Regards Martin.

MartinW wrote:I don't know whether it would work on a tank but we have a couple of local shops doing vinyl wraps on motorcycles.
You would have to be extremely careful about not spilling fuel around the filler neck and the area around the neck would have to be painted.
Regards Martin.

What do you mean by vinyl wraps?? Applying a vinyl plastic material to the tank? Not heard or seen of it myself. Will ask around. But my preference is for metal. Still might have to clear coat to maintain the polish or polish a lot.

This is a  example of a couple of sites (there are lots) that do vinyl wraps on bikes and cars, the advantage is that if you wish to change it at anytime it can be removed with the aid of a heat gun. I bought some bits of a guy who had vinyl wrapped his car and was doing a Brick café racer that I think he was going to wrap. I had a talk about how hard it was to do and he said after watching a few You Tube videos and a few stuff ups he now had the hang of it.   https://secureservercdn.net/198.12.144.78/l2g.63c.myftpupload.com/wp-content/gallery/home/BikeColourchange.png 
https://linehousegraphics.com.au/motorbike-racing-graphics-kallangur-brisbane/
Regards Martin.

Not sure about the aluminium brazing rod idea. Never done it, but I have used the rods for fabrication and stuff with varying success. The finished braze is usually a dull grey colour (at least with the brand I've used) but then I've never really tried to flat it and polish it as you're thinking. Main issue for me would be the heat you are putting into the tank to achieve a braze. Ally doesn't glow a different colour to let you know it's up to temp - one second its there looking normal and the next - a hole! The lead thing uses the fact that lead flows at a temp where the metal bodywork is still relatively cool so you've a big margin to work in. The ally brazing rods require the base ally to be at quite a high temperature, so you're much closer to catastrophe. Ally expands quite a bit with heat too, so distortion could make things tricky, as could the high thermal conductivity - which tends to mean that you have to keep pumping a lot of heat into to your work area. I'd guess that your idea would be more suited to sharp, smallish nicks and dings - almost like repairing a hole. The lead thing makes me think of large, shallow depressions, and I'm not so sure about that. I'd love to see how you get on, 'cause ideas like this are great.

...Just thinking, what would be wrong with trying plumbers solder? s'basically lead and it would stick to cleaned ally?

chris846 wrote:...what would be wrong with trying plumbers solder? s'basically lead and it would stick to cleaned ally?

Using it would present the same challenge as brazing—developing sufficient heat for it to stick without deforming the tank or burning off the flux first.

Lead is unlikely to polish well or match texture with the tank. Repainting the tank with suitable materials, technique and patience is the most viable alternative.

Lead?  I don't think they even use it in the factory anymore. I had a bike where the previous owner used that aluminum brazing stuff to repair some corrosion holes in the tank.  That stuff is hard, and would be a really hard job to sand smooth.  It's for welding and filling holes where finish isn't important.

You want to get a quart of this stuff:

https://www.bottompaintstore.com/duraglas-fiberglass-filler-24035-1-quart-p-10555.html

Duraglas is better than regular filler because it has glass fibers in it that make it much stronger.  It's also more waterproof than regular fillers because it's made for use on boats.

You can get it at a local West Marine store.

There are people who do paintless dent repair that can pull the dents out without damaging the paint. 

Have you ever painted or done prep work for a paint job before?  Your post doesn't sound like you have.  Post some photos of your tank, and describe what you are trying to accomplish ie. are you doing a custom paint job, or a factory color repaint. 

What is your budget?  A good paint job with a factory color isn't cheap, but it doesn't have to be crazy expensive either.  There are many here who have painted their bikes and can walk you through to good results.

chris846 wrote:Ally doesn't glow a different colour to let you know it's up to temp - one second its there looking normal and the next - a hole!

FWIW, and I wouldn’t risk a tank on it, when bending/annealing ally a few stripes from bar soap around the work area will burn when it’s up to temp.

A good panel beater will do a top job for not a lot of $$$

chris846 wrote:...Just thinking, what would be wrong with trying plumbers solder? s'basically lead and it would stick to cleaned ally?

There was a phrase from the last century "Mad as a Hatter" regarding folks who did leading on the in vogue hats of the time. My understanding is that it didn't take long or much lead fumes to make serious impact on one's intelligence. Back in the sixties, I was shaken loose of the Carny I had started out with and in need of employment for the summer and landed in Chicago in the loop at midnight. Anyway checking in with the local employment folks they tried to send me out to a auto shop to do leading. The boy is dumb but not quite that stupid.  If you don't mind I think I'll pass on anything involving melted lead.

jjefferies wrote:There was a phrase from the last century "Mad as a Hatter" regarding folks who did leading on the in vogue hats of the time. My understanding is that it didn't take long or much lead fumes to make serious impact on one's intelligence.

It wasn't lead causing the damage; it was mercury.

Laitch wrote:

jjefferies wrote:There was a phrase from the last century "Mad as a Hatter" regarding folks who did leading on the in vogue hats of the time. My understanding is that it didn't take long or much lead fumes to make serious impact on one's intelligence.

It wasn't lead causing the damage; it was mercury.

Exactly, there was a factory I called on back in the 80's that made temperature controllers that used mercury in the manufacturing process.  The place was unbelievably creepy.  People who worked there for a long time were almost normal, but would have little nervous things like weird eyes or shaking/twitches.

Obviously,K owners then

I'm with .75 on using a form of bodyfiller. In either case, it's going to take time and a lot of patience to recreate the tank curves. Been there, done that, succeeded, don't want to do it again.

Post a couple photos of your tank.  What are you trying to accomplish with it?  Is this a custom, or are you doing some repair and a repaint?  What is the present condition? 

There is a booming industry of specialists in dent repair who can pull out dents without having to repaint the repair.  They do most of their work on lease vehicles either for owners who need to turn in an undamaged vehicle, or for dealers who are reselling lease returns.  You might want to have one of them look at your tank.

Some collision shops have someone who can do that work.  Another place to find one is at a place that sells materials to the local collision shops.  The best guy around my part of the world works in a building that is part of the local car wash.

You would need a really dry tank and you'd need to soak it in Carbon monoxide, (sort of like hanging the tank off the exhaust pipe of a car and let it idle for half an hour) But if there is a difference in colour when you've done it why not make that a feature and do those panels that polished colour and the leg indents the raw Alloy colour. We do two tone paint so why not this polished two tone?

What would people say to partially filling the tank with water and leaving the side to be worked on upper most 
for getting the heat treatment?

Thanks for the correction on lead vs mercury. Think I still have a bottle of mercury somewhere out in the garage. And think I will still avoid lead or mercury.

Regarding the original question, I purchased the "Durafix Aluminium Welding Rods Brazing" and decided to educate myself. Despite all my best efforts the purchase was out of China. Somehow that tidbit of info escaped me when I looked at all the different offering on Ebay of the same material. The Chinese CAN do decent work but you never know what you're going to get until after. Anyway short version of long story, they shorted me by a couple of pieces of material and when I protested the supplier, EtoMall, refunded my money. Unexpected but it served, as in my testing using scrap metal I found that the lower temperature benzomatic type heaters (based on youtube videos) weren't sufficient to heat the target and melt the brazing rods and when I used a higher temperature ox-acetylene torch it was way too much and the target aluminum melted. So I never got near my gas tank and the whole thing served as a test. Then I fell back to the time honored approach of pushing the dings out. Got a piece of steel, bent it and proceeded to push until I got the dings mostly out. But someone else previously commented getting the appropriate curves back is a not possible. At least for this  DIY person. An artist might have different luck. Tank is now restored to something approximating the original shape. It has no holes and is available for body putty and painting.  Whereas what I wanted was to polish just the bare metal. Oh well. I've since gone on to new adventures with fuel injectors, gas filters, and clutch spline lubes which I will post in another thread.

Someone, Laitch I believe, posted about how to attach photos. I had several that I wanted to post. But the problem has been not posting the photos but hosting them as this forum does seem to have provision for that. I seriously can understand that as it would push the costs and no one makes any money off of running a forum. But I tried to host the photos on other servers and found myself getting deeper into problems in that direction. Out of that struggle apparently I somehow seem to have signed up to have my own forum- Not my desire-. Anyway would post photos but until I figure out how to host the photos it ain't gonna happen. Thanks for the comments and well wishes. I'm off to fix my shower plumbing. Almost as intractable a job.

I've done this once on a steel tank. Metal has a memory and some dents if not to bad will respond to the heat it up with a hot air gun then rapid cooling with dry ice. You might have to do it a couple of times and a push from the inside might help when in the cooling stage. Don't overheat the paint it should be still intact. Freeze spray might be an alternative to dry ice.
Regards Martin.

MartinW wrote:I've done this once on a steel tank. Metal has a memory and some dents if not to bad will respond to the heat it up with a hot air gun then rapid cooling with dry ice. You might have to do it a couple of times and a push from the inside might help when in the cooling stage. Don't overheat the paint it should be still intact. Freeze spray might be an alternative to dry ice.
Regards Martin.

Not an issue with paint, Martin. I removed it all with paint remover and a wire brushing before getting to this point. But this sounds like an interesting technique. Though the tank is aluminum rather than steel. Still worth giving it a trial. But at this point I've pushed the dings out for the most part. Does leave a few new dings from the inside though. But those I've felt I can push back in with a soft hammer.

I tried to braze/solder my tank ... one of the fuel connector things broke off. The heat got dissipated so fast I could not get the braze/filler rod to melt/flow

BTW I did a mechanical workaround ... bolt with a hole drilled down the shaft for the fuel ... insert from the top through the filler cap ... nut on the outside. I made Al washers out of 0.5mm Al sheet. It worked well.

I didn't scrap a badly dented tank after a spill. I pushed the dents out to make it workable again, and re-polished it (it had already been stripped and polished) The tank looks absolutely fine to me - we go back a long way together, it looks cared for, that's the main thing. Not much in life is pristine, and if it is, it probably isn't being used properly