Bridgestone 100 GP cafe build

[stickman]

just got my powder coat oven, will have a powder coat gun this week, will be doing the same thing to a 100, will post before and after photo's
stickman

[motzingg]

Last week i was working in little chunks as much as possible, still didn't get much done. Pretty depressing really, i pulled the engine back out of the frame, removed the forks to weld on the fender stud and paint them, and started matching up all the hardware i bought.

The first problem to come up was the fender stud, i tried to weld it on but did a bodgy job, didn't have a 'hot' enough welder i guess and didn't get a nice weld on it. Also, the hole that was ripped in the fork tube turned out to be a bigger problem than i thought. Where it pulled through the insides were all ragged and holding up the piston. I diassembled the entire fork tube, and i'm not quite sure what to do now. It probably should be replaced alltogether. Anyone have an extra 'right' fork leg laying around? The inner tube is in pretty good shape, so a fork with a rusty inner could work for me, otherwise i'll have to machine something? Hone it? i dont know, this is a tough one.

Second I got my top end apart and found that the chrome is chipping around the exhaust and one of the transfers. Pretty bad, there is about a dime-sized area flaked off right now, and knowing how this sort of thing goes, its only going to get worse. Its probably not bad enough to keep this bike from running, but its definitely terminal. What does a new cylinder for one of these cost? NOS or used i guess i don't care.

Then third i noticed a lot of oil in the bottom of the crankcase. So this was either siezed and someone poured oil in the cylinder to loosen it up, or there is a bad crank seal on the transmission side. Crap, looks like the whole motor will have to come apart.

So much for an easy build, i was hoping to ride it yet this fall, but it might be more of a winter project now.

In good news i got the tank burned out with acid, went well and now it is sort-of clean. Definitely nothing a fuel filter cant handle. And no leaks! All the stainless allen-head hardware on the engine looks real pretty too, unfortunately its all show-no-go right now.

Also, has anybody swapped cylinders from other bikes onto these? I'm sure its been done... Maybe a KE125 cylinder would be close, that is rotary-valve at least, i have no idea if any of the other dimensions line up. I think a buddy of mine has one of those he might let me tear down and measure.

[motzingg]

so i was just reminded about this thread by someone asking me a question.

if anybody is still curious i've been making slow but steady progress on the G/P. new kid, school, work, and at least 4 other active moto rebuilds. hard to remember where i left off.

well, i re did the fender mounting stud and got that TIG welded on, stripped the forks down and painted them.

I got the front end completely sorted. I made an 'executive' decision to leave the original fork seals, as they were pretty tight (the fork boots did their job very well) and the springs and tubes are pretty clean.

Everything got resprayed in OEM silver (or rather, honda OEM silver, close enough) including headlight and tins, fork lowers, etc. The wheel was in pretty good shape, one of the prior owners put a lot of work into polishing the chrome rims. The front brake could definintely use new pads and a tune up, but the bearings have a bit of clean grease in them and that can all wait til its on the road. The steering assembly took a while, the fork ear tin pieces were mangled and took a bit of persuasion to line up, also the bearings i found for the steering neck were a bit too big so things were spaced out for mounting the fork ears. Took some persuasion but everything is fitted and looks pretty good considering how rusted and mangled they were to start with. She's not gonna be perfect, just so long as all the cancer is eradicated and everything works ok.

The engine finally got the seals it was missing. The clutch was missing a throw out rod or something... didn't have the manual handy to figure out exactly what was missing so i just machined a brass rod to go in the throwout mechanisim. The 'cam' gear thing was riding flat against the clutch, probably caused by some p.o. inspecting things in there then loosing it.

Cut a new gasket for the gear case and reassembled everything. The 5mm screws holding on the injector pump were stripped so they got tapped and fitted with new socket head cap screws. The injector pump has one of the banjos broken off so that needs to be addressed, probably will have to machine one out of aluminum hex rod or something, but i was able to get it refitted with some small urethane line (4 or 5 mm) and the whole area looks a lot cleaner and should be leak free.

The kickstart shaft seal is shot, but that can wait until later, didn't have one handy when i was putting this together christmas weekend, and bearing shop was closed.

uhhh what else? thats about it. sandblasted some small frame bits. got the new handlebars fitted, they are from a CB100 project that is going the direction of cafe racer/track bike to gun against the cb160s in local racing, stock throttle and controls mounted to clubmans proved to be too much pain in the ass, so i will use the bars and controls on the bridgestone, which should compliment the forward controls and more control for riding doubles and so forth.

i'll take some pictures when i dig it out of the back corner of the shop to drop the engine back in.

[motzingg]

Just wanted to let anyone following this know, I finally got my Bridgestone progress written up on my blog.

I documented the repair of the kickstarter engagement cog on the back of the clutch. Both engines i had were broken. What a PITA!

http://outofcontrolmopeds.blogspot.com/p/bridgestone-100s.html

thanks for lookin' while you're there you can check out my moped projects!

[Richard Clark BS parts]

You did such a nice job, I wish you would post your entire article here for all to see, in the future!

Richard Clark

Questions? or need Bridgestone parts? call:

Richard Clark
812-944-1643  8am-6pm EST Weekdays

[Sno Jet]

You get an A+ for your documentation and writing style.  Easy to follow.  Wish we could all provide that kind of information including clear pictures.    Thank you.

[motzingg]

Glad you guys are enjoying it! I'm trying to do a better job of doccumenting these sorts of things, the blog lets me have total control and go back and edit. Dont worry, it will stay where it is for a long time, but I will continue to update it and revise it.

I'll try to remember to post when i make major updates.

I'm trying to get the TMX running for 'Frozen Snot Ride' a bar crawl that happens on the day of the daytona 200, at some bars around Milwaukee. Usually there is snow, so the vintage moto club here brings out a lot of cool vintage enduros and MX bikes... guys running wide open cr250's, hodakas, some flat track bikes show up. Two years ago there was a full blown RZ400 in race trim with no silencers... motoboner!

Milwaukee cops look the other way for a day and let us ride just about anything with wheels and a motor while drinking from 8 am to 2 pm... or later. The TMX should fit in well and represent bridgestone.


As far as fixing this other cylinder, now that i've gone to the work of fixing the clutch, has anyone pressed-in a cast iron sleeve? Having a machine shop at my disposal it would be pretty easy to machine the sleeve, and i could get radical on the transfer ports after boring it out, but as far as specifics, how thick to make the sleeve, how to retain it, what kind of clearance to the cylinder... i have no idea.

Otherwise, what does a good used cylinder for one of these go for these days? The TMX came with a nice NOS piston, but no rings.  I have talked to US chrome about different projects before, and the $300+ price tag for replating the bore is way out of my reach, if i can't come up with something for less than $200 i'm going to sell the TMX and pick up a dirtbike motor for the GP.

If i were to sell the second bottom end with the CR steel cog in it, what would that be worth? $100? more?

[old smokey]

Hey motzingg,
Are you near Milwaukee?
You could see what Millenium Technologies in Plymouth, WI could do with your cylinder.
Probably no cheaper than chrome, but others say the Nickel Silicon Carbide plating is a good alternative.
See their link below.
They mention a cylinder exchange program, but probably no BS parts though.

http://www.mt-llc.com/

[motzingg]

Awesome, just got off the phone with millenium, $175 for the replating... thats actually not bad at all considering how much time it would probably take me to machine and press in the cast iron pipe.

I'm in milwaukee WI.

just got done talking to some people this weekend who are part of the AHRMA GP200 class racing around the midwest. Most of them are running 175 hondas, but apparently the bridgestone would qualify... i thought it was 4 stroke only, but they said two strokes are allowed up to 175cc!!! Holy crap, I wish i had bought that BS175 when i had the chance. A 175 rotary valve twin wouldn't even be fair competition against the honda lumps...

I'm still pretty well set on getting the CB100 built for this season, but I might start pushing the 100G/P build toward a raceier spec. With good porting and a pipe, 20+ hp should be no problem with this bike, the only question is, will the transmission/clutch stay together?

[ddog71]

Did you install a generic regulator/rectifier on this bike.? I'm still trying to figure out how to do it for my 175's & 200's that I have. Have a great day... Tim

[OldSwartout]

Holy crap, I wish i had bought that BS175 when i had the chance. A 175 rotary valve twin wouldn't even be fair competition against the honda lumps...

You wouldn't believe how fast those Honda "lumps" are.  I still can't...    They are regularly beating all the two strokes that used to run up front.  Just check the results pages at ahrma.org for the 200GP class.

Here's what happened at Willow Springs this year: http://www.ahrma.org/ahrma_pdfs/results/2013/rr/13_rr_willow_day1.html