1971 Bridgestone TMX100

This is a 1971 Bridgestone TMX100 trail bike. I got this of Marketplace in April 2024 for $250. The price was low because the engine is seized and there was no title. It is almost complete though, the only thing missing is one tiny reflector. I am going to do a frame-up resto-mod on this one.

Bridgestone made motorcycles very briefly in the 60-70’s. Supposedly the big 4 in Japan (Kawasaki, Yamaha, Honda and Suzuki) told Bridgestone to stop making such awesome motorcycles or they would stop buying Bridgestone tires. So Bridgestone stopped making motorcycles.

This one has a 100cc, 4 speed, rotary shift engine. It has two rear sprockets so you can change the gearing “easily” for street or off-road use. I love everything about this bike, the look, the feel and the story.

As of 6/25/2024, this is a current project of mine that I can’t wait to get into! Here are some photos from the day I picked it up. It had some Air Force Base stickers on it from a base that no longer exists.

I started the disassembly by taking off the carb to clean it. This comes stock with a Mikuni VM18 carb which is what I had on my black Motobecane. The carb is hidden behind a cover with the oil pump in there too. The oil pump was locked up so that’s probably why the engine is seized.

I also took the original battery out that looked a little rough. I’m sure I will be replacing the entire wiring harness.

I also took off the seat and gas tank. The tank had some nasty, super old gas in it. I cleaned that out by soaking it in degreaser. Next I am going to soak it in some evaporust. The original orange paint looks amazing in the sun but I think I’m going to strip everything and repaint/powder coat.

I need a few specialty tools to get this engine apart. So far I’ll need an exhaust wrench, flywheel puller and a puller to break the seized piston loose. Last night I made the flywheel and cylinder pullers. I made the exhaust wrench puller in Fusion360 and I think I'm going to have it made by SendCutSend.

The pullers I made from scrap metal and weld-nuts. The weld nuts are 10mm. I just drilled the holes in the steel plate and welded the nuts on. For the flywheel puller the three 6mm bolts will thread into the flywheel and the center bolt will tighten against the crankshaft. For the cylinder puller I will have to thread the stud holes and use 10mm bolts to attached the plate to the cylinder. The center bolt will push against the piston and hopefully push it apart.

Both the cylinder and flywheel came off perfect with the puller. First I snugged up the bolts on the flywheel puller so they were tight but not over tightened. Then I tapped all around the puller with a hammer until the flywheel popped off. I had to use an impact screw driver to get the last screw off the stator plate. I’m going to replace all the philips screws with allen head screws when I rebuild everything.

The cylinder also came off easy with the puller. The only problem was the bolt on the puller wasn’t long enough. I had to drop a socket and a fork nut in the cylinder to get some more reach when pulling the cylinder. I tapped the cylinder holes with 10mm tap to bolt the puller on. I also cut a plastic disc to drop onto the piston so I wouldn’t damage it (even though I doubt it will be re-used). There are videos of both on the @theroadhaus Instagram!

Next I started to take apart the transmission side of the engine. I needed an impact screw driver for every bolt. The case opened easily and there didn’t appear to be any damage or metal shavings in there. Of course my socket set ended at 22mm and I needed a 23mm socket to take off the clutch nut. Unfortunately the plastic oil drive gear is cracked in two places. Who is 3D printing them???

Since I had to break until I went back to my shop to get a 23mm socket, I decided to make some more tools…

The exhaust nut was ridiculously stuck. I couldn’t get it off with a punch and hammer so I decided to make a special wrench out of 1/4” steel. I made it in CAD and cut it out on a water-jet.

Since I was already making the exhaust wrench I also decided to make a new flywheel puller. One of the holes one the one I made by hand was off by a little bit so I had to dremel it out.

I also decided to make the Dealer Tool that holds the drive sprocket in place while taking the clutch nut off. I made that on the water-jet and welded in two pins that slide in between the sprocket teeth.

All the tools look good and fit perfect but I haven’t had time to work on it yet. Maybe this weekend! (8/24/24).

I took the clutch apart first. The tool I made was useful but the nut was almost finger tight, it loosened up will almost zero force. The clutch plates all look really good, I don’t think they need to be replaced.

Before I started on the engine a friend told me they have a problem with the starter teeth breaking off. So when I took this apart I found that all 4 teeth were broken off. I am going to try to make a press fit replacement instead of replacing the entire gear.

The rotory intake was intact, it looks rusty but I was surprised to see that it isn’t made of metal. The material feels like an abrasive cutoff wheel for a grinder. Everything else in the case looked pretty good!

I took off the drive sprocket and I tapped the crank a few times with a rubber mallet and the cases didn’t budge. I had to use a Tusk Case Splitter to split the cases. I’ve never used one before and it went super smooth. I threaded the supplied rods into the flywheel cover screw holes and put the puller on.

I used my impact gun on the puller. The case split right away but it only opened the front half. I didn’t want to split it unevenly so I tapped the back of the case with a rubber mallet as it opened. That got it to open evenly.

I had the case sitting horizontally so I could film it for Instagram, that was probably a mistake since a bunch of the gears fell out when I split it open. I should be able to get it back together with the help of the manual though, Lol.

Once everything was disassembled I threw it in the parts cleaner. I have a 15L Ultrasonic so I can put one case section in at a time. At first I was trying some degreaser but wasn’t impressed by it. Then I tried some Dawn Dish soap and it worked amazing. You only need a little bit and it cleans great. I set the temp to 80C and the timer to 30 minutes. Here are some photos of the clean cases/parts.

Once everything was clean I was able to see some repairs to the case. It looks like the previous owner filled a broken section around the stator in with some JB Weld. It also looks like there was a hole in the case they filled with an aluminum weld.

The oil pump was locked up so I took that apart too. One tiny, little 1/8” steel ball was missing. The copper colored piece was locked tight so the pump wasn’t working at all. The oil tank was also still filled with motor oil instead of 2-stroke oil. I have to get a replacement ball for the pump and I can reassemble that. I’ll probably make my own case gasket for it.