OK, you asked for it. I use either wire brushing in my drill or bead blasting to clean off corrosion,. If you are talking about built up oil and plain dirt then here are some additional suggestions that I have collected over the years.
1) Normal wash: Good only for removing pure dirt and light oil. Use your
favorite cleaner (I prefer Dawn dishwashing detergent over Simple Green or
other "automotive" cleaners simply because a strong detergent gets the most
of this type of crud off with the least effort.)
2) Pressure wash: Removes heavier dirt and oil but not any corrosion.
Recommended only for whole engines. Avoid spraying at any exposed seals
(like around the countershaft or tachometer pickoff, possibly the exhaust
header seals, too). OK to hit normal gaskets.
3) Dishwasher: For individual pieces you get results similar to a pressure
washing. Of course cleans the insides of pieces so be sure to blow air
through passages to get out residual water. Do or don't tell your spouse
about doing this depending on which path minimizes negative spousal
reaction. (Mine was pretty skeptical - sniffed the dishes that were in with
the parts to see if they smelled like oil.)
4) Sand blasting: Sand (silica or carborundum particle) blasting will
seriously remove metal and leave an uncorroded, but pitted surface.
Particles may become imbedded in aluminum if air velocity used is too great
and/or the alloy is particularly soft. Use with incredible care if at all,
especially on pieces with oil/water galleries. If you do, mask off all
possible entrances carefully since any grit that gets in will be difficult
to completely get out and any left in will likely destroy something in your
5) Bead blasting: Small glass beads which shatter on impact clean off
surface crud and leave the aluminum looking like it was tapped with a
zillion microscopic ball peen hammers. Same warning on keeping grit out of
6) Shell blasting: Ground up walnut (or other hard) nut shells are the
gentlest of the three blasting methods. Removes crud and shallow corrosion
and leaves the surface looking the most like it originally did. Note that
the blasting methods are the only ones that will get corrosion off metal in
the nooks and crannies.
7) Kerosene, paint thinner, gasolene, naptha (in decreasing order of
flammability and increasing order of volatility, I think): Use to remove
oil, oily dirt, and tar. Use a wire brush or toothbrush to assist in
getting off thick gunk. Does nothing for corrosion. Build/rent/buy a parts
washer to speed cleaning of dissasembled pieces.
"Gunk" or equivalent: Gunk combines a petroleum-based solvent and a
detergent in one can. Does a pretty good job on heavy dirt and light oil,
nothing for corrosion. I think using a heavy detergent wash to remove heavy
dirt, then a separate treatment of solvent to get heavy oil/tar off, and
finally a second detergent wash works better than trying to do it all in
9) "Carb cleaner": is xylene and/or MEK (methyl ethyl ketone), i.e. an
active, very volatile solvent. Good for getting the "varnish" and "parafin"
that form on the inside (and outside) of carburetors from old gasoline.
Good as a general solvent, too.
10) WD-40: The solvent doesn't work as good on varnish as real carb
cleaner, but of course WD-40 leaves the surface protected due to the oils
in it. Use it immediately after you have de-crudded (like that verb?) and
brushed/blasted to keep surface shiny.
11) Hydrochloric acid: (available as muriatic acid). Takes off corrosion
(not oily gunk), bubbling as it does so, but leaves the surface dark grey.
Use a stainless steel wire "tooth" brush ($1 at your local car parts place)
to expedite activity. Don't use it unless you really like this color. Avoid
12) "Etching formula mag wheel cleaner": Available in a spray bottle and
labelled "B" on the ABCDE specifier for automotive cleaning products, it
contains phosphoric and hydrofluoric acids and bubbles when applied. Use a
stainless steel wire "tooth" brush to expedite activity. Avoid the fumes.
Leaves a dull light grey finish which can be lightened up by wiping with a
paper towel/cloth immediately after brushing with the wire brush.
13) Gasket remover: Water-based liquid that softens fiber gaskets so they
can be scraped off without damaging the machined surfaces. I mention it
here because I found two uses for it: 1) it softens up the carbon and crud
on the inside of the cylinder head, the ports, and the valve heads, which
eased scraping those parts clean considerably. 2) It seems to
soften/dissolve clear-coat (and other paint as well - be careful where you
paint/spray this stuff!)
14) Wire brushes: You can get ones that fit in your drill and brush either
circumferentially or radially (oh hell, go look at them) and in different
wire thicknesses. I recommend the softest wire for aluminum. Also get the
wire "tooth" brush (and more than one) I mentioned above. Look in the
welding section of your hardware store if you don't see them in the tools
section. You can also mount a wire wheel on your grinder for small parts.
Frankly, wire brushing (and blasting) are the only things I've found that
clean off corrosion and leave the surface bright. It's a lot of work and
can't get in the nooks and crannies but gives the best results. Clean
surface with solvent first to keep brush from simply smearing the crud
15) Scotch-Brite pads: Available in about 6 by 9 inch sheets for a buck,
they work well on clean, smooth aluminum to brighten it up, don't do squat
for rough-finished aluminum.
16) Aluminum jelly: I tried this stuff years ago so don't remember exactly
what it is (more acid-based stuff, I guess) and was disappointed in the
results. But then perhaps that was when I still hoped for some magic method
that didn't involve elbow grease.
17) Don't use steel wool on aluminum. Tiny bits of it will break off and
stick in the aluminum. These then rust and you are left with "rusty
Additional non-aluminum specific cleaners:
18) 3M metal-stripper-wheel. This is a round plastic sponge, impregnated
with abrasive grit, which you chuck into your electric drill. These remove
tar, paint, rust from steel frames, tanks, panels. Probably a bit too
abrasive for use on alloy, though. With one of these wheels, you can remove
all the paint from,say, a gas tank without using any evil chemicals. It
also removes surface rust, leaving you with bare metal covered with a
network of fine scratches, ideal for paint adhesion. You then swab off your
part with "metalprep", wash it off with water, dry it thoroughly, and paint
away! That new paint will stick like glue!
19) Get yourself a can of "Carburetor & small Parts Cleaner". This
milky-white stuff will take the hide off an elephant. It'll take carbon off
the tops of pistons. It'll clean your carbs good. Just don't put any
non-metallic parts in it. You just dump your castings, jets, etc into the
can ( get the kind that comes with a dip basket ), and fish them out a
half-hour or so later. Bright-squeaky-clean.
20) Another good carb cleaner is Berryman Chemtool. This stuff is about as
poisonous and flammable as gasoline, but at least it's a good cleaner.
Berryman's comes in a spray can, and its great fun to spray it on a grease-
and-varnish encrusted carburetor; the stuff just liquifies and flows away.
I personally use chemtool to clean carbs I don't want to take apart or off.
21) Spray it heavily with Gunk and leave it covered over night, then scrub
with those plastic scratch pads. For the corrosion, Aluminum Jelly works
good, but do it after you rinse the engine cleaner off. My engine came out
looking great. Chuck Stringer <firstname.lastname@example.org
22) Being the sort who hates paying more than $50 for a motorcycle I've run
into a lot of corroded aluminium and have had good luck with
scotchbrite(tm) pads (plastic wool) followed by Nevr Dull. Nevr Dull
doesn't have much problem cleaning up the scratch marks left by really fine
scotchbrite. This works pretty well on both smooth and sand-cast surfaces,
though it doesn't get the all the crap out of the sandcast surface, which
in my book is Ok because it doesn't make it look like you've got nothing
better to do with your life than sitting around polishing your crankcase
(hmm, sounds like a euphemism...). For bad corrosion (or shitty castings -
like old ducatis) I've had to bead blast followed by 320 grit followed by
400 grit followed by 600 grit followed by Nevr Dull, but it's usually just
easier to buy another motorcycle. The progressive stages of sandpaper can
also be used with some success to take the sand cast marks out. As for the
jugs, good luck. A brass brush will take out what crap it can reach, but
you probably can't find one long enough. It shouldn't leave any visible
scratch marks on a rough cast surface if that's what you've got. Bead
blasting will cure it for sure. Latte' Jed <email@example.com
23) In general, the rough cast cases clean up pretty well with some
aluminum cleaner or carb cleaner solvents available at auto parts stores.
Tide works ok, a brass bristle brush works really well. You *don't* want to
polish the cases with buffing wheel, etc. Polished side covers, like most
of the older British and Italian bikes had, are fine, but polishing the
engine cases themselves will cause the engine to retain heat. If you do
complete disassembly and have stubborn corrosion/need for resurfacing, a
bead blaster with walnut shell grit works wonders. Finding someone to do
this, however, is often a bit of a trick.