Rusted gearbox/phosphoric acid disaster! Advice needed!

[watchhislegs]

Hi folks, I recently split the cases on an engine of unknown origin I have had for a number of years. The gear clusters were both a little rusty and therefore I decided to chuck them in a bit of phosphoric acid I had lying around the bedroom. Now, phosphoric acid has always been great for me at removing rust however it has now given my gearbox a very dull finish and has completely removed any shine/polish they once had. You can see how dull they are next to the shiny rod that goes through one of the gearbox shafts. Should I be worried or do you reckon it will be okay? Answers on a postcard please?

What is the copper coloured coating on the inside of the cogs?

[bare]

You had Phosophoric acid (Metal Prep) in your bedroom. Clearly not someplace Wimmin frequent.
Liklely you left the bits in solution a wee bit too Long. Metal prep is intended for wiping.. Not soaking :-)
ALL you can do is reassemble and HOPE that you have not done any serious damages.
PS; that Copper is actually Brass... when unmolested.

[steeley]

hmmm its got the rust off nice.as bare said reassemble and try it.i did a similar thing on a ypvs gear box some years ago I used a diluted solution of the rust remover from machine mart.the bearings from the box were shot and some of the gears had some rust on.the gears came out ok ,but there was also rust on the selector forks which I soaked separately .mistake, it removed any rust but also took the chrome plating off the forks and I replaced these.the gearbox went into my tzr 350 and has performed ok till now.

[watchhislegs]

The acid wasn't really in my bedroom.

Headcoats, that's what I was worried about although surely it shouldn't change the underlying properties of the metal, just remove rust and leave a coating on the surface.

[muddyfox]

by the creepy avatar, you dont use the acid to get rid of bodys?? was it next to the chloroform lol

[arrow]

If my chemistry knowledge servers me correctly the dull surface is a micro thin layer of iron phosphate. The case hardenind will be unaffected. Get some oil on them asap and all will be well. Once oiled they will be nice and shiny again, and jet black.

When you get the motor running I would suggest changing the oil after 150 miles or so. It will be black with iron phosphate from the gear teeth. The 'coating' on non touching parts will stay where it is.

[arrow]

I don't think they are affected. The acid will not go for the bronze.

[watchhislegs]

Great stuff gents, thanks for that. I'll sleep soundly now.

[steeley]

oh just to say after I ran my engine with that box, on one occasion when I was going into a round about braking hard the gear box whined a bit. I think there could of been a bit more oil in it lol.

[chippy348]

Feb 17, 2015 0:46:53 GMT 1 watchhislegs said:

What is the copper coloured coating on the inside of the cogs?

Re the copper this bit of text will explain it.

Heat Treat Stop-off

Steel parts to be heat treated are sometimes copper plated to allow for subsequent “selective” heat treating. After plating (and before heat treating), one or more areas of these parts may be machined to remove the copper plating. During heat treating, the areas of the part without copper will be heat treated while the areas with sufficient copper plating will not be heat treated and will remain more ductile.
After the heat treatment process is completed, it is then quite common for any remaining copper plating to be removed (by stripping) from the steel parts.

[watchhislegs]

Thanks chippy, really interesting that.

I love this forum, everyone is so helpful.