RestoCycle How-to: Derust chrome exhausts and parts with phosphoric acid

[NobleHops]

This is a fast and effective technique that an old hot-rodder taught us to really tidy up a tired-looking exhaust or other chrome part on an old motorcycle. No, it's not going to look like you just had it replated, but it's going to look a whole lot better!

Before and after using this technique, using phosphoric acid and 0000 steel wool.

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Here's the patient - a very solid but tired-looking exhaust system for a 79 Honda CBX. We don't have the budget for a set of reproduction pipes, and so we're going to make the most of the pipes we have.

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Typical of the condition of a 40-year old exhaust for a bike that spent time in the real world - it's still perfectly solid but there is good surface rust in several locations where it was impossible to stay on top of.

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Collector and heat shield, clamp. Not terrible, but they look tired. If you look super closely, what you discover is that the rust spots you see sort-of "bloom" on the surface of the chrome, and actually originate from much smaller pits and imperfections on the thin surface of the chrome. This will really clean up, wait and see.

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Muffler, same. Solid and with no perforations, just tired-looking.

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[NobleHops]

Step 1, very important, get it clean! We need to remove all the dirt and grime and looser rust that we can, or else it will just scratch up the chrome when we do what's next. We're using spray cleaner here and paper towels, even better might be a soapy spray and a pressure washer. Get them clean, degreased, free of any debris. You can leave them wet.

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Ready for action.

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We like this stuff a lot for this purpose, it's mostly phosphoric acid, but a product called Ospho would work just as well. Add 1 part of this to 4 parts water in a spray bottle and put some nitrile gloves and eye protection on too while you're at it. Find this at an auto paint and body supply.

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Count those zeroes please, there are four of them. Three zeroes will scratch, four, used properly, will not. Aluminum foil would NOT be a good choice for this in concert with the phosphoric acid, don't do that.

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[NobleHops]

Now spray down the pipe pretty generously with the solution, let it soak for a few minutes. Keep it wet. Notice how much pressure we're not using on the part, fingertip pressure with the steel wool on the part. Rust-b-Gon!

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...and it doesn't take long either. A big benefit of using phosphoric acid for this is that as it cleans the metal and dissolves the rust, it also passivates the bare metal in the pits in the chrome where the rust was formed, leaving behind a durable layer of iron phosphate, which will leave the surface protected and resistant to re-rusting for a good while.

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Header pipes, greatly improved.

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Yes, that looks a lot tidier, right?

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Side by side on the mufflers. Does it look new? No, but it looks tons better, and it's stable too.

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[NobleHops]

Side by side near the headers and the collectors. It would be a good idea to finish with a quick polish using something that leaves behind a waxy coating, just for another layer of corrosion protection, but we've done it with and without and they looked great.

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[CLCB]

Thanks Nils

What polish stands up to the exhaust heat the best, especially the header pipes?

[NobleHops]

We use a product called QuickGlo (no longer sold) and also Mother’s. Both seem to work fine for a garage queen.