View Full Version : Grit Blast Stombergs

03-01-2008, 09:54 AM
I have some "practice" CD 150 Strombergs and was wondering about grit blasting the outside to clean them up. 30 years ago I found out the hard way that doing this to the AMALs on my BSA 650 was a very quick way to strip the finish of the metal. While the Strombergs are for practice, I do not want to ruin them. Any guidance? Mark

03-01-2008, 10:34 AM
It depends on the media you plan to use. Glass beads would be as aggressive as I would go. A more aggressive media will cut into the surface.
Glass beads will clean the surface and leave it with a semi dull cast.

03-01-2008, 11:22 AM
Be very careful. The metal you take of can not be put back. Be particularly with those areas that have cast in id numbers and words.

This is the procedure I use.

1. remove all loose crud with a stiff bristle brush.

2. de-grease with a mild solvent- carb cleaner is OK.

3. blast at 40-50 psi with walnut shells.

4. polish with 40, 80, 120, 400 alum. oxide compound (Harbor freight has the little cakes and polishing wheels.) Get several of the wheels and don't mix compounds and wheels or you will have to start over again. In other words dedicate one wheel to #40, one to #80, and so forth.

5. finish polish with rouge compound.

6. coat with UV resistant clear (check out Eastwood site)

good luck

03-01-2008, 11:23 AM
Try walnut shells first. Then glass bead. Or use old glass bead to minimize the cut. Plug all orifices first.

03-03-2008, 08:48 AM
Old glass bead is broken and will leave a matte finish. Use fresh new glass bead at low pressue - below 55 psi for a beautiful satin finish. Glass bead starts out round and peens the finish smooth. The more you use it, the more the beads will break up, leaving your media sharp, which etches the surface you're blasting. Or use a more expensive plastic blast media as that will leave a nice polished finish. Make sure to tape off mating surfaces so the interior stays clean and dust free. I've never had much luck with walnut shells, but that has more to do with how my cabinet is set up and what parts I clean most often.

03-03-2008, 09:45 AM
Walnut shells are great for cleaning things like diff gears, leaves them just like new and doesn't cut like other media.

But the process with glass beads that you mentioned and is often forgotten is to keep the pressure low. I start with 40psi and work up if I need to.

I'd love to give plastic beads a try but @$2/pound, maybe not.

Here's a good reference

I've used glass bead, scat magic, speed bead, aluminum oxide, and lots of black beauty. I keep 5gallon buckets of each type which about fills my cabinet hopper.

03-03-2008, 09:56 AM
Be very careful.

6. coat with UV resistant clear (check out Eastwood site)

good luck
Consider a coating. I find that the freshly exposed surfaces are prone to rapid oxidation. Fluffy whitish clumps appear overnight.

03-03-2008, 11:30 AM
Hey Jeff !!

I hope you're well and not snow bound.

How does on bring back the wonderful finish
you creat on your rebuilt dizzys? Mine has
dulled down quite a bit since I installed it
over a year ago.

Dale in Puerto Rico

PS- After two year's effort, my TR6 is finally
on the street and seems functional. Your dizzy was
a key component in getting the engine running.

03-03-2008, 06:08 PM
Peter: If you have a local Grainger store you can get plastic bead media for approx. $1 per lb. if you buy 50 lbs

www.grainger.com (https://www.grainger.com)

03-03-2008, 06:11 PM
To Dale et al:

It did reach 55 degrees in Philly today with 60 forcasted for tomorrow.

Put that in your pipe and smoke it! :yesnod:

03-03-2008, 08:26 PM
Thanks Frank. I'll check them out sometime when I'm down in Portland.

03-03-2008, 08:28 PM
To Dale et al:
It did reach 55 degrees in Philly today with 60 forcasted
for tomorrow. Put that in your pipe and smoke it! :yesnod:

A big, whopping 60*F, huh??

I ain't impressed one lick, buddy. You and Pat look mighty happy
at 80*F eating 'sghettis at Il Bacaro on the Old City San Juan.



03-04-2008, 10:38 AM
Nice painting.