How to repair pitting?

[Starfire]

Before doing anything to a part that you plan on having chromed, take it to a chromer and get some advice from them.

Anything you do can make it harder for them to work their magic, and/or be a waste of your time.

The first option is the expensive one, but will give really nice results.

[Spindevil]

high rpm 3m scotchpads FTW

working with aluminium is always gonna be tricky, very soft metal that scratches easily and cant be buffed out

my brother got afew of his cast ally engine parts acid dipped and they came out all nice and shiny and new looking.

be warned that even with fine grit wet/dry the best finish you're going to get is 'smooth but dull' (aluminium oxidises almost imeadiately) and u'll never get it shiny again unless u'r getting it re-chromed.

take it to the chromer and get a quote on the job and some advice on how to prep it.

if they offer to prep it u might wanna consider as it may be worth it to save you sll that time and stress

[Ribfeast]

Start with 180 dry sandpaper
Then 240 wet
Then 400 wet
Then get a rag mop wheel for your bench grinder, use a cutting compound, eg Josco grey or brown, looks like a chocolate bar. This will get rid of the fine imperfections.
Buy a ventilated flap wheel or some sort of soft buffing wheel for your bench grind, and use an aluminium compound, such as Josco white.

This is mine so far:

Nearly there!

[rob20v]

Starfire is right, take them to a chrome plater and ask their advice. You could also try to find someone that repairs chrome bumpers and grills as I used to get old Jaguar grills repaired and they came back like new after accident damage. I think they were called Moray Grills in Moray st South Melb. This was years ago but I am sure there would still be people doing this sort of work in every state.Try a place like this.Hope the link works.

http://www.aclassmetal.com.au/profile_introduction.htm

[thechuckster]

the metal in TA bonnet grils is a much, much, much softer than the stuff you find in alloy rocker covers.

The kind of polishing work you do for a 1G rocker cover will destroy the TA vents.

[joey]

Ok guys, finally update time. (ive been a little lazy)
I took ur guys advice and sanded them down... works a treat, they're as smooth as a babies bum (despite the look of it on the picture there is no actual indentations of where the pitting used to be).
Got an uncles mate who works with metals (not sure exactly what) to do the best job he could on repairing the crack....






It seems very strong now but the only minor problem is that he was a little rough on the top side and there is quite a large abrasion mark from one of the tools he has used (tried to show it the best i could in the second pic). Any idea as to whether this would show once chromed?
I had a talk to my mate whos dad runs a large industrial type plating factory and when he asked what type of metal it is i explained its cast aluminium... he then said that practically any other material is fine to be chrome plated but he reckons that the aluminium gets eaten by some of the ingredients in the mix
I explained to him that numerous amounts of people that have these have got them chrome plated and he just basically said to make sure that it is actually cast aluminium and if so he will have a go but to his knowledge it wil eat them a bit.... is this right?
Cheers, Joey

[oldcorollas]

aluminium can be dissolved by both caustic and acidic mixtures...
so if pH is too high or low.. your bits are gone...

[kremsra28]

alsacorp make an awesome chrome paint, its very durable and looks awesome, however it does cost a bit i think, nut it could work out a cheaper option if you wanted to do a few things, i cant remember the ecact website but do a google on custom paints or alsacorp,
i think you can see it here also http://www.tcpglobal.com/kustomshop/

if you went down this road, i would sand them back wit either 120 - 180 dry, get some spray polyester, give them a few coats of that, guide coat it and sand it smooth wit 180 dry paper, then give ithem a few good coats of 2k primer, guide coat and rub smooth wit 800wet, i think form memory that you need a black base for the chrome paint, but it says on the website anyways,

maybe its wat you looking for, maybe not, but good luck wit it!!

krem

[lt1972]

If you havent already had them crome plated, you could just polish them up like ive done to all my alloy parts.
The timing cover as pictured was extremely pitted and tarnished (extremely grey)
Alot of elbow grease required and days you just wanna give up but the results are pleasing
Start with 180 grit then 320 then 800 then 1200 then finish with 2000 (all must be wet paper)
After that finish off with wadding polish and a protectant
never ever ever ever use a rotary wire brush, (you will wand to smack your head against a brick wall if you do...from experience.)