View Full Version : Transmission case finish

04-03-2009, 12:23 AM
Got my 4speed apart and want to refinish the case. Any wisdom out there?

I bead blasted the motor cases and primary covers and other alum parts. Was ok with the finish on the case, but the primary came out rougher than I think it should be.

The tranny case is in good shape...just 40 years of crud on it. How do I clean it up and make it a bit shiny without roughing up the metal (like beadblasting does)?

I have searched for local soda blasters but have not found one...so looking for alternate methods of cleaning.


04-03-2009, 12:53 AM

Not sure if you saw my reply to your similar question (http://www.antiquemotorcycle.org/bboard/showthread.php?t=14156) about motor cases in the paint section.

But I posted a pic showing the results of the process I used. I also show detailed pics on my restoration blog (http://www.grandpasharley.com/main/blog/Entries/2008/10/24_Factory_luster_Restored.html). I did blast my cases first but the Wheel mist and rubbing compound approach may work after a good scrub down in the parts washer. I am not certain though as I have only used that approach to undo a finish that was to bright and shiny from improper blasting. It worked well for my situation to undo the bright silver paint looking finish.

Hope this helps,

04-03-2009, 08:08 AM
Thanks Josh,
i had not seen the blog before and that really helped! is crushed glass more or less abrasive than media blasting? It "feels" more abrasive and i'm looking for less abrasive. Like your results and a tranny case is a lot easier to do than a motor case so, i'll try your technique!

04-03-2009, 02:49 PM

I can't take the credit for the Wheel mist/rubbing compound method to restore aluminum, I found the link to Backyard Bob's page (http://www.harleyhummerclub.org/members/backyardbob/index.html) on here, but indeed it worked wonders.

To answer your question...

is crushed glass more or less abrasive than media blasting?

Crushed glass is more abrasive then media blasting, and also more abrasive then glass bead blasting. Crushed glass is exactly that, glass that has been crushed into a fine grit, (I don't recall the size I used.) It has sharp jagged edges making it more abrasive then glass beads or media. I have been told that crushed glass is like using silica sand or aluminum oxide having similar grits.

Glass beads are round spheres and they don't attack the surface in a way that severely etches the metal. It does clean the surface grime off, but peens the surface at the same time. Like shot blasting but with out all the apparent dimples

If I were to do my cases again, I would not use crushed glass at all, I would only use #7 glass beads. I wouldn’t even us the Wheel Mist/rubbing compound method after that. The #7 glass bead gave me a nice clean patina finish on my Lifter blocks alone. Unfortunately I had already used the crushed glass and beads on my cases, so I was forced to do something different, that’s when I reverted to the Wheel Mist/rubbing compound method.

In finding this all out I need to determine what method to use for my tranny case. In order for it to match my motor I have a feeling I am going to use crushed glass, glass bead, and Wheel mist/rubbing compound. I am going to first start with the glass bead and see how it compares.

Remember, you can always try blasting the inside of that case and see if it gives the finish you are looking for.

Bill Pedalino
04-05-2009, 05:23 PM
The judges may disagree, but I really don;t go crazy withthe finish. After several months in the oxygen, the aluminum turns and they all look pretty much the same.

I've been using No. 10 glass beads on harley motor and transmission cases for over 40 years. After initial degreasing/cleaning and blasting, I use a soft brass brush to tone down the white appearance left by the glass beads. After a few weeks of oxidation, the aluminum still looks almost like factory castings.

Extremely importand! You must commit to very arduous cleaning in HOT HOT sopy water whenever you glass bead aluminum parts. The metal MUST expand during the cleaning process to ensure that all beads are released from the surface. WHile imursed in the hot wash, scrubbing with multiple sized medium-stiff plastic brushes is a must as well. I use the brass brushes during the cleaning after scrubbing with plastic brushes. Don't forget to ues your small round (1/8"-3/8") round bore brushes as well.

Yes - a lot of time dedicated to cleanng. But in all these years and afer many, many motors, I've never had a problem related to residue abrasive. (Thank God!).

05-07-2009, 10:39 AM
the best finish i have been able to achieve is i glass bead all aluminum parts but the mistake most people make is they glass bead with too much pressure. an inline regulator is cheap. you should use as little pressure as possible for your situation. most dirt cleans off aluminum easily. also you should hold the nozzle of the bead blaster as far away from the part as you can as long as it is getting off the dirt. it may take a little longer but well worth the effort. after glass beading soak it down with wd-40 and use a stiff brush to scrub it. with a little wd-40 once in a while the finish will stay as good as day one because it has i think nitrogen in it that keeps out the oxygen and moisture much the same as a scope one a rifle. hope this helps