Use Harpic to clean headers? DON’T

[gsxbarmy]

If ever you have considered (or do) use Harpic to clean your headers - then don't. Basically it's a mild acid (not a bleach) which over time causes damage. Watch the video as that gives a good explanation.

https://www.youtube.com/watch?v=EPlccjMBaTQ&feature=share

Instead I would suggest Belgom Alu applied with rough stockingette.

[KoZi]

Interesting... I did a lot of polish staineles steel pipes on my mates bikes and never had any problem.
After Harpic i use a lot of water and a wet sandpaper and then polish finally. 
Ofc you have be careful to any other things near exhaust - bolts etc. Harpic could do damage...

[Irish in Oz]

Pickling paste is acid as well, bleach will also pin hole stainless steel. Really if you are going to use chemical do as KoZi said, you can also put bicarb of soda on after to neutralize but then it's alkaline, I was given this information by the chemist that makes the pickling paste. Or just buff and polish until your hearts content, I'm not sure what they put in polishing soap.

[Hooli]

Alloy wheel cleaner is slightly acid (or alkaline, I forget which) too. It's how these things clean.

[Del]

the thing is to watch what your doing - I use harpic all the time I wear big cloves and put it on with a scouring pad - rub it on get rid of grime and then after a few minutes I jet wash it off and then wash with soapy sponge - Im very careful now as left it on too long and discoloured the pipes took me an age to polish back up

[Irish in Oz]

Alloy wheel cleaner is slightly acid (or alkaline, I forget which) too. It's how these things clean.

Hooli
It is Phosphoric acid, usually diluted when you buy in shop so it's about 10-15% active.

[VladTepes]

What about those 'acid free' wheel cleaners?

[gsxbarmy]

What about those 'acid free' wheel cleaners?

Interesting thought - but not sure they will work. Wheel cleaners are designed to dissolve brake dust mainly, as opposed to burnt on dirt (like an exhaust). I have some acid-free wheel cleaner though, and next time I clean my headers I'll try it and report back, as there may be some merit in it.

[VladTepes]

It works on wheels and brake dust etc on the car anyway. Not tried on bike yet.
Not sure if it would be any use on headers.

[Irish in Oz]

It will be interesting to hear the outcome.
Phosphoric acid has little affect on stainless steel, it is good on old chrome and nickel parts can be left overnight in solution and come up bright but it will surface rust again so will need some type of sealing.
Pickling paste mainly Nitric acid is the best for stainless and is very commonly used by tig welding shops to remove the oxidation from welding which is the tarnish you get on your header pipes from heat.
I don't have much discolouration on my header pipes probably because I have a standard silencer