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tank de-rust and hand shaping

erikwillke

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I've searched but couldn't find exactly what I was looking for.

I have two tanks for my 73 CB750. Both have rust in them. I eventually want to hand shape the knee pockets. Should I de-rust the tanks first or shape them first? I know that by shaping them I'll knock some rust free and possibly undo what I had done by treating the tank but I fear that the intents will make it harder to convert the rust after it's done.

Thoughts?
 
How bad is the rust and what method are you going to use to remove the rust. for very bad rust either electrolisis method or muratic acid works well, you will have to seal tank after either process. I would do indents first as not to damage sealent in the process. IMO
 
I was going to do the acid one. I was thinking the same thing. I didnt' want to seal it and then bang away at it. thank you for the input. btw, the rust is extensive. like flaking away extensive
 
Evapo-Rust.jpg

May I suggest Evapo-Rust, I used it on a recent Honda GL1000 gas tank and it removed all rust. You can buy it at Harbor Freight or most auto parts stores.
Don't forget about flash rust after I just coated the inside with Marvel Mystery Oil.
Good Luck.
 
Are you sure it is in fact rust? Most of the tanks I see are coated with old gasoline that has turned to varnish. Looks like rust...I start with acetone or similar through in some marbles or something similar and give it shake let it sit and do it a couple of times...normally cleans it right up if it is varnish and not rust.
 
I had a tank that had 1/4 inch of varnish in the bottom, rust up the sides and top of tank. Let it soak an entire week with acetone shaking evryday with about 40 1/4 inch nuts in it, hardly even softend the varnish. Muratic acid washed it out in less than an hour with out the nuts. Looked like brand new inside, coated with Caswell sealent to keep it that way. If your tank is really rusty you may have to deal with pinholes.
 
I used vinegar last year on a couple of very badly rusted tanks. Loaded them up with nuts and bolts and plugged the bungs. Let it sit for a day or so and every time I passed the tank, I would give it a good shake. Rust was literally annihilated. When you are ready to flush, drain vinegar (save it for another tank), flush tank with fresh water and blow dry with compressed air. Immediately fill with fresh gas. Run with a fuel filter. I've had no probs. I think it ended up costing me about $10.
 
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