Be careful using oven cleaner, as suggested above. It can turn your nice case a dull, dark, grey. 

it is a very strong acid, it is made to clean aluminum wheels, you can only get it this  from a distributor, any auto detail mobile supply truck should have it,   

Air2Air: I think you missed a spot......

(joking... nice work!)

Vespa, what chemical are you talking about? Is it paint/powder coat/anodizing safe?

if you have any friends that work detailing cars i would get ahold of them , they can get wheel acid from there distributors that is alot stronger and better that the weaker acid you can buy on the shelf at a parts store, this will really clean your aluminum parts, i buy it buy the gallon and use it on my aluminum wheels on my other cars, it works wonders on brake dust, 

When I did my motor over recently, I wanted an original look. I had it in pieces so it was easier but I cleaned everything REALLY well and then used an aluminium cleaner I bought from NAPA and a toothbrush. This stuff is wicked caustic but really does the trick. Spay it on, let it sit for a little and start scrubbing. Comes out looking very nice. Actually just used it on an aluminum motorcycle case that was coated and stained with so much mud I was surprised it came out...but it did.

you can use any brand oven cleaner. then wash off.  easy peasy. it will degrease and leaves a nice aluminum color. becareful not  to get it on painted areas you want to keep painted

Absoultely. I've used it on every engine I've ever painted. You can get it in a rattle can at your local O'Reilly's.

is there such a thing as high heat clear or ?

Image Gallery

Coopertune Steve paints them clear, an idea I jumped on since it's a sensible way to look original yet protect it.  And when you want to clean it, no scrubbing - the yuck just slides off.

I then went crazy and polished and clearcoated the carb, other aluminum stuff and even the brass radiator and overflow and so far so good.  Even has a bit of extra gloss.

Almost a year later the engine compartment looks basically the same...Thanks Steve.

Well then I'd go with the power washer and some good detergent. Get a coarse and fine brush as well. You'll probably have to do a little scrubbing.

really dont want to tear everything down  motor running fine   so sandblasting is over kill

If you have access to a blasting cabinet, you can blast it with baking soda or Aluminum Oxide.

If you wish to leave the transmission looking natural alunmin pressure wash and clean using a alloy wheel cleaner to remove oxidation. 

have whole subframe sitting on shelf with motor tranny all attached

tranny looks like its oxided or/

whats best way to clean  polish or?

do most leave natural or paint? if left natural should I clear coat?