'73 Suzuki GT250 - Part 16 - Stainless steel front brake disc

I had an opportunity to cut a front brake disc for my GT250 out of 5 mm thick stainless steel sheet using abrasive water jet cutting. After googling and looking at different front brake disc designs I decided go with similar style used in aftermarket Triumph Speed Twin front brake discs. Once I was happy with the 3D-model I exported it to a DXF file which was used to program routing for the cutting machine. 

After cutting I machined grooves around each bolt hole used to fix the brake disc to the front wheel hub with 14 mm square mill in a vertical milling machine. Once that was done I sand blasted the disc to get a good surface for paint. 

This time I decided to use simple spray paint. Before painting I masked outer edges of the disc and cleaned all the surfaces I wanted to paint with acetone. I applied a thin coat first which supposed to help the next heavier coats to stick better. Instructions in the can said to use primer when necessary so I opted to leave it out. I'm curious too see how it works without primer. If it doesn't I will prep it and paint it again. Once paint had cured I installed the disc with a 12 mm spacer I also got cut with abrasive water jet cutter and rolled the bike outside to snap few pictures of it 😊

Design for front brake disc

Dimensions

Blank

Grooves for socket cap screws machined with square end mill
in a vertical milling machine

Sand blasting before...

...masking and coat of matte black spray paint

Dimensions for spacer

I painted the outer surface also with matte black

'73 Suzuki GT250 - Part 6 - '79 Suzuki RM 125 rear wheel refurbishment

Since I’m using a ’79-80 RM/PE 250 swingarm in my GT250 I figured that it would be easiest for me to fit same type of rear wheel to go along with it. I made a want-to-buy add to our local vintage MX forum requesting a ’79-80 RM250 rear wheel.

I had almost forgot my add when I received a phone call from a guy nearby. He had a pile of parts from a ’79 RM125 for sale including a rugged rear wheel, which would acquire quite a lot fixing up. Rim on it had cracked from several places and spokes were warped. After being outside for couple of decades lots of rust had formed in the brake drum and bearings were seized in place. 

'79 RM125 rear wheel (right).

Disassembling was the first thing to do and getting the beat up tire out with help of couple of tire irons and some lubricant. I needed to save few of the spokes and nipples so I applied some rust remover to them, screw them out with a spoke wrench and marked them masking tape. I removed the ones that were badly jammed or had cracked nipples with an angle grinder. Bearings were easy to get out after heating the housings with a hot air gun.

Couple of tire irons, spoke wrench, 1 mm cutting disc
for angle grinder and rust remover.

Rear wheel hub, bearings, spacer, spokes and nipples.

Rear wheel didn't come with a brake shield so I bought one from eBay and disassembled it.

'80 Suzuki RM125 rear brake shield

Due to heavy use and load bearing housings on the sprocket side tend to wear out and become loose. One way to fix this is to turn the housing bigger and fit a new steel bushing to it, which then holds the bearing. I send my hub to a machine shop located in Kokkola, Finland, called Konepaja Ågren to get it fixed up.

Pair of 6202-2RSH/C3 rear wheel bearings (15 x 35 x 11 mm).

I marked the worn bearing housing with a red marker pen.

Fixed housing with a new steel bushing inside.

Once I had both rear wheel hub and brake shield I masked them for sandblasting. I used old parts (rear sprocket and bolts, caps etc.) and masking tape to protect surfaces I didn't want blast. I also cleaned the brake drum before blasting with rust remover and a sanding pad. I took blasted parts to one of my local paint shops and got them painted black.

I used old parts for masking to protect surfaces I didn't want
to get sandblasted.

Painted rear wheel hub and brake shield.

I cleaned the brake drum with rust remover and a sanding pad.

I was looking for a new rear wheel rim and I got an offer of a new old stock (NOS) 18" x 1.85" Takasago rim with 36 holes. Since it had a reasonable price I decided to purchase it. Surface of the rim had stained during storage so I cleaned it with some Autosol Metal Polish and Autoglym polishing cloth.

NOS 18 x 1.85 Takasago rear wheel rim.

Storage stains on the surface of the rim.

Autosol Metal Polish and Autoglym polishing cloth.

Surface after polishing.

I picked one inner and one outer spoke from sprocket and drum brake side of the hub (4 total), marked and send them to Wheel Factory Finland, a company which makes custom spokes and nipples. I decided to try stainless steel spokes in this project. I've used their spokes before on couple of my bikes and been very pleased with them.

Model spokes marked and ready for shipping.

New set of stainless steel spokes and nipples.

Dimensions for '79 Suzuki RM125 rear wheel spokes.

I assembled the hub (bearings and spacer) before putting on the spokes. I used an axle seal (20 x 35 x 5 mm) to cover and protect the sprocket side bearing. I will turn a new bushing for it when I start lining up front and rear wheel sprockets.

New axle seal (20 x 35 x 5 mm).

I began lacing by placing all of the spokes to the hub, lubricated every spoke thread with boat tar and screwed them to the rim with nipples. Once I had the whole wheel together I took it to my local village shop. They do lacing for bicycle wheels and were able to line up my wheel and tighten the spokes for a fair price.

Bottle of boat tar.

I lubricated all of the spoke
threads with boat tar. 

Assembled rear wheel.

I've wanted to try white vinegar for rust removal for a while and brake shield parts seemed suitable for this experiment. I set rusted parts to a plastic container and filled it up with white vinegar. Placing the container to a warm location sped up the chemical reaction. Vinegar quickly turned to brown color and after a while to black. Unfortunately after keeping the parts a bit too long in the solution it had build up a black gooey layer on the surface of every part. I cleaned it off with warm water but it left black stains, which I had to soda blast off.

Rust removing with white vinegar.

Parts after white vinegar treatment...

...and after soda blasting.

Now that I had rust free parts I decided to try bluing them. I bought a bottle of Birchwood Casey's Perma Blue, a liquid gun blue. Bluing is simple process, which starts by applying the solution to surface of cleaned and rust free parts. I used a small paint brush. At first the surface turns black for a while. After the solution dried out off the surface I washed it with warm water. Last step was to oil the surface to bring back the black color.

90 ml bottle of Birchwood Casey's Perma Blu

First three stages of bluing: rust free (bottom),
applied (center) and dried and washed (top).

Dried parts after applying bluing solution.

Oiling the surface brings back the black color.

Lastly I replaced some of the worn parts with new ones. I ordered a new OEM bushing (09319-10008), washer (08211-15341) and pivot dust seal (61262-22A00) through my local Suzuki parts dealer. I bought a new TA2225Z roller bearing (22 x 29 x 25 mm) from eBay for a more reasonable price than the OEM one. Unfortunately the new bushing didn't match with the original spherical plain bearing so I have to find another one or use the old one instead. I also bought a pair of EBC S 617 brake shoes.

Bushing (09319-10008) didn't match with
the original spherical plain bearing (left).

Pair of EBC S 617 brake shoes.