Refinishing Aluminum Engine Parts?

As part of my E30's slow restoration, I'd like to refinish my intake manifold and valve cover before reinstalling them. I'm asking GRM instead of an E30 forum since I feel like this crowd always has better answers for this kind of stuff.

In short, I'm looking to replicate the OEM finish. Here's a pic for reference:

http://bimmertips.com/wp-content/uploads/2016/06/bmwm42.jpg

It's a semi-matte sort of finish, looks like bare metal to me.

It seems my options are painting and/or media blasting. Painting seems to be the easiest and cheapest option, but I'm concerned it will look, well - painted - rather than the bare metal look I'm going for. Is media blasting the correct choice here? Any recommendations are appreciated.

The aluminum paint looks great from 20 feet away, but up close it looks like paint. I did that on an old P4B intake after I cleaned it with Purple Power that was a little too concentrated and it mussed it up. Good aluminum color, but looks like paint up close.

I would media blast (fine sand) and clear powdercoat in a matte finish. I have tried clear paint, but it browns and peels. I don't recommend soda blasting. Its a bit too fine and ends up making aluminum look like primer grey paint.

You could set up a home anodizing bucket

I like media blasting aluminum with glass bead. It leaves a almost natural cast finish and you can then clear coat it or leave it plain.

I've been reading about glass blasting and it seems to be what I'm looking for. I'll probably go for that as long as it isn't too expensive.

Douse it with plenty of Cosmoline for that factory look :

Google Vapor Blast

If you're blasting your inlet manifold, make sure you seal it up well. You don't want grit getting in there it can be a real pain to get rid of once it's in there and for obvious reasons, you don't want blast grit getting into your engine

If you want it powder coated, shoot me an IM

Ask your buddy that works for a A/C company for some "Coil Cleaner" it will clean and renew the factory finish.

If you media blast use walnut shells not sand or glass.

Glass or sand will cut, walnut shells will sort of burnish it.

jimbbski wrote: I like media blasting aluminum with glass bead. It leaves a almost natural cast finish and you can then clear coat it or leave it plain.

+1. It leaves a very original looking finish.

What about soda media?

bentwrench wrote: If you media blast use walnut shells not sand or glass. Glass or sand will cut, walnut shells will sort of burnish it.

I have done a couple E30 6 cylinder motors now. For the aluminum valve covers, intakes, and oil pans, I just put a stiff wire brush on an old electric drill and buzz away at them. It generates a little dust but no grit to speak of.

The results don't look 100% brand new. But it's a great look, very age-appropriate yet clean and tidy. Also, it doesn't last more than a couple seasons if the car lives outside, but it takes essentially no time to touch it up.

Photos of an example are about halfway down this page:

M20B25 pics

Just this weekend I used medium glass beads to strip an aluminum triple Weber intake that was previously painted. This intake has easy access to the balance tube, so there were no issues with getting all of the media out. With a more convoluted intake, that could be a real challenge. With finer beads, you get a bright finish that is still a bit satin. It matches the ceramic exhaust coating well. I considered spraying it with clear. but that always seems to yellow over time. So I'm leaving it natural.

Have any of you folks tried Rub 'n Buff? I saw a thread over at Adventure Rider on the topic, and I could think of at least a hundred bare-cast things under the hood that could look a lot better with this stuff.

Examples:

Media blast with glass beads will give you the best even looking finish. That said glass beads are very difficult to completely clean off a porus surface. The smallest amount of glass bead residue will wreak havoc inside an engine mainly because they are so hard and will embed themselfs in softer materials like main, con rod and cam bearings. Aluminum foundries use steel grit to finish castings to a even finish.

You might try cleaning with a really good degreaser and then follow with a some watered down muratic acid or a product called Eagle Magnesium Cleaner and Etch found at auto parts stores. Some air conditioning/heating repair companies use a product named Hydro-Kleen (other brand names out there) to clean the fins on compressors and condensers and it leaves a bright finish. I think this stuff is basically muratic acid with maybe an additive or two. You can't be too careful using any of these! Rubber gloves, eye protection and a well ventilated area because the fumes are nasty!

Thanks for all the suggestions guys - this project will be this weekend. Can't wait!

I need to have the car all buttoned up and ready to go before the end of the Thanksgiving weekend, so I'm not sure I'll have time to bring it to get media blasted. I'm thinking of using one of the chemicals recommended here.

In reply to Mezzanine:

How durable would that stuff be I wonder?

pirate wrote: You might try cleaning with a really good degreaser and then follow with a some watered down muratic acid or a product called Eagle Magnesium Cleaner and Etch found at auto parts stores. Some air conditioning/heating repair companies use a product named Hydro-Kleen (other brand names out there) to clean the fins on compressors and condensers and it leaves a bright finish. I think this stuff is basically muratic acid with maybe an additive or two. You can't be too careful using any of these! Rubber gloves, eye protection and a well ventilated area because the fumes are nasty!

I've used the Eagle One stuff before. NAPA sells a similar product, it's called aluminum brightener or something similar. It works well, but as mentioned it's nasty stuff - wear proper protection when using.

I went from this:

to this:

to this:

Used simple green and brush/hose. Then a HF soda blaster. Finished with high temp aluminum engine paint.

Used it before and it looked great for years. These are on bikes that don't get tons of miles, but the paint is more exposed then a car intake.

As per the advice in this thread, I went to NAPA and got a bottle of EagleOne Etching Mag Cleaner.

It came out great! I'll post pics of the results tomorrow. I degreased the parts first, and then sprayed on the cleaner before scrubbing with a stiff brush and finally rinsing.

In the past, cast aluminum engine parts never really came out completely clean using just degreaser. The etching cleaner actually completely cleaned/restored the finish, so I'm happy. Thanks for the suggestions!

Before:

After: