The Cessna 120-140 Association Forum

Are they aluminum or magnesium? Rotating my tires and found some corrosion I would like to address. Part# 161-03000 I think, the inner half next to the brake disc. Not the half that has the hole for the inner tube fill.

Found it, magnesium. A different set of rules for touch ups and spot treatments for corrosion.

Ar you sure? I was going to say aluminum, but I wasn't positive... Corrosion on magnesium is black.

It's a long, convoluted route but...

Cleveland Experimental kit 199-25301 lists aluminum wheels (and brakes).
199-25301 includes 40-75B wheels.
40-75B wheels use 161-03000 inner wheel halves.

Cleveland conversion kit 199-46 fits Cessna 120/140s
199-46 includes 40-97A wheels
40-97A wheels also use 161-03000 inner wheel halves
Ergo, Cessna 120/140 wheels should be aluminum.

To add confusion, my brake assemblies are definitely magnesium, but I think my "conversion" was more a transplant from a 150 or something.

John, I found a Cleveland Wheel Manual with the material information for the 40-97A assembly. It's too big for me to attach here but I sent you an email copy, scroll down to page 9.

Well, we have two pieces of information from Cleveland that do not agree!

Cleveland says Cessna 120/140 conversion kit 199-46 uses wheel 40-97A. Wheel 40-97A uses inner wheel half 161-03000. Inner wheel half 161-03000 is also used in wheel 40-75B (among many others). Wheel 40-75B is used in Cleveland Experimental Kit 199-25301. Cleveland Experimental Kit 199-25301 is listed as having aluminum wheels and brakes.

Yup, my maintenance thing from Cleveland says magnesium. I just got a message from Spruce that says they are aluminum. The corrosion I noticed is pitting. The quality of the casting leaves a little to be desired. Cleaning with MetalPrep79 leaves a dark grey color.

Pitting in magnesium often makes the part look like a sponge. The metal turns grayish black. On aluminum it's more likely to look like a light gray or white powder.

To me, magnesium parts always feel so light that they are like styrofoam, not metal.

You could always try putting a match to it!

Pitting in magnesium often makes the part look like a sponge. The metal turns grayish black.

This.

Am proceeding as if it's magnesium. Chromic acid (DOW 19) conversion coating followed by real zinc chromate primer.