How to remove surface rust w/o abrasives?

[nyyankees588]

So I am finally getting around to registering our vehicles down in CA since moving from WA. Cue the smog check challenges.

Unfortunately the catalytic converter on the van has enough surface rust that the codes printed in to the metal are barely visible. Since it isn't the factory cat, the smog shop is is required to use those numbers/letters to verify that the aftermarket cat is appropriate for the vehicle. I've worked at it with some fine sandpaper, WD-40 and PB Blaster and have been able to discern 80% of the characters, but the sanding is gradually making everything fainter/harder to read.

Does anybody have any suggestions for removing surface rust w/o using an abrasive that will sand down the metal and make the letters unreadable? Or any other tips for how to handle this? I'd love to avoid having to buy a new cat to resolve this...

[BCam]

Have you tried reading them with a light shining obliquely on the converter?

If that doesn't work, if you take a photo with your cell phone, the numbers might show. You may need to adjust the brightness and contrast either on your phone or on a computer. I've done this several times on different things with unreadable text or numbers. Adjusting the color sometimes help and conversely, converting to B&W also sometimes works. Wiping with water, paint thinner or some other solvent may also bring out the unreadable text in a photo. You'll have to experiment with the light as well when taking a photo.

In any case, I wouldn't do anything physically to the converter unless a smog shop rejects it. I'm sure they deal with this all the time and the visible characters may be enough for them. They also may have some tricks.

[Mikerson]

Clark’s solution will do what you want, but that is not stuff you want to breath or get on you. How about a rust converter? Maybe the old detective trick of holding paper up to it and then rubbing the wide side of a pencil on it?

[nyyankees588]

All good ideas - I've tried wiping and lots of different angled light. Will try enhancing a photo and the old pencil and paper trick.

[BCam]

Originally Posted by Mikerson

How about a rust converter?

The rust converters I've used have resulted in a coating of sorts that could further obscure the numbers.

[JWA]

If any one line of numbers is visible I'd Google search that to see if something comes up better identifying what cat you might have.

[Lilnuts2]

Navel jelly or the old school of coating it with molasses and letting it sit for a few days, goggle it.

[BroncoHauler]

Originally Posted by Lilnuts2

Navel jelly or the old school of coating it with molasses and letting it sit for a few days, goggle it.

I was thinking of Naval Jelly too, but I haven't used it in years and years.


Herb

[snowdragon3]

maybe use rust remover, WD-40 makes one that Home Depot sells. Ive also used another brand, but cant think of the name of it. Since you only need the area where the code is, I'd tape a plastic bag up to it and fill it a bit with the liquid. Enough that the liquid is touching the metal, but not too heavy to break loose the tape.

[E-350]

Not sure how it looks right now and whether or not the number have been stamped in.
But if you would paint it in red or green or so and THEN use 1000 grit sand paper you might just remove the paint on the sheet and NOT in the grooves...