1972 GT380 engine covers

jhood · Post by **jhood** » Wed Dec 02, 2009 6:55 am

Ok, here is my question. I am restoring (2) GT380's and on the the engine covers the original color is a light brown almost like it was varnished at the factory. This coating either comes off or gets scratched and looks not so original. Does anyone know what I should do to the covers to restore the color to original looking condition?

Or would blasting them with aluminum oxide (soda) or whatever brighten them up so that they would have the polised aluminum look? If I were to blast them would they tarnish if left uncoated with something? What about blasting the crank cases to give a brighter look?

I appreciate anyones thoughts and experience regarding this topic as everything is still in a pile on the garage floor.

Thanks,
John Hood

Coyote · Post by **Coyote** » Wed Dec 02, 2009 8:26 am

Take a look at the photos in this post I have linked you to

http://www.motorcycleracer.net/phpBB2/v ... php?t=2167

This is what you get from fine media blasting. It's not shinny but rather a satin look and feel. The big plus is it removes all traces of any previous coatings. It gives the surface a great prep for repaint or powder coating as the blasted surface has a little 'tooth'. Maybe someone here knows how to duplicate that original color on the cases but I would suspect that it is not paint. More likely it is powder coat. Put a little paint stripper on a hidden area (underside). If the coating is reluctant to come off, it is powder coating. Blasting removes that as well but takes more effort as it is a lot tougher than paint.

Post by **Suzsmokeyallan** » Wed Dec 02, 2009 8:32 am

The main cases were painted on a lot of the bikes and since they have fins etc, cleaning this way prior to painting helps prepare the surface properly. This cannot be done successfully without using a blast media process since the casted surfaces are too difficult to reach properly with a brush etc.
Glass beads work well, but do not buy the coarse ones, use #8 or finer grit which gives a bright satin finish.
You mainly want to clean the surface of residue and oxidation plus give it a bit of grip for the new paint to adhere.
Baking soda can also be used if the cases are clean already but just need the crevices working over to reach those areas. It also works great for carbs and fuel taps, but its a weak abrasive cleaner so dont expect it will scour away the gunk on cases.
The case covers always get corroded from age and exposed weathering so its best to use the glass bead media on them first to remove the surface issues and smoothen the surface before working up to a polished finish.
You cannot blast the surface and just leave it, you need to either paint or polish it after as the aluminum surface is now OPEN and it will draw in contaminates faster than before.
As always the air pressure, the angle, and the distance of how you work the gun gives different results so need to pay close attention to what youre hoping to achieve finish wise.
Heres a Titan lower case i was working on so you can see how the #8 glass bead will clean it up prior to painting.
If the cases have some gouges and such from POs bad work or casting issues you can file and sand on them now so once the glass beads are applied it looks tidier.

tz375 · Post by **tz375** » Wed Dec 02, 2009 1:38 pm

John,

That yellow - brown coating was a clear coat that was applied at the factory to stop the polished cases from corroding.

We now know that it yellows with time and small scratches lead to spider webbing under the clear coat.

Use paint stripper to remove it, polish the covers and either coat with a rattle can clear coat or just polish the covers from time to time.

Barry S. · Post by **Barry S.** » Wed Dec 02, 2009 7:37 pm

Didn't some of the 380/550's have a slight gunmetal color the the cases?

Coyote · Post by **Coyote** » Wed Dec 02, 2009 8:47 pm

I'm with Barry here. Yamaha did the same treatment on alot of the early cases. Sort of a gun metal finish was present on my showrom new 68 DT1.

H2RICK · Post by **H2RICK** » Wed Dec 02, 2009 9:26 pm

Yes, I seem to remember the 380J models had some kind of unusual colour on the cases of some of them. Same thing for the 550J's as well.
Maybe Suzuki discontinued it in mid-year in a cost saving effort ??? Or they ran into problems with the coating process ?? Another unsolved mystery.....

Rustygt550 · Post by **Rustygt550** » Thu Dec 03, 2009 10:18 am

Yes the 380J,K & 550J,K side cases & ram air covers where finished in a Gunmetal clear coat the finish
can be copied by putting a couple of drops of black/brown paint into the clear.
Here is a nos gt550K Points cover

jhood · Post by **jhood** » Fri Dec 04, 2009 12:00 am

Thaks to everyone who has posted replies. This gives me some really good ideas of how to proceed with my restoration.

Regarding the application of the clear coat, what would be the best way to apply it?

Thanks again to all,

John

H2RICK · Post by **H2RICK** » Fri Dec 04, 2009 6:26 pm

Thank you for the pic, rusty. That clears that up, so to speak.