Bridgestone Racer

going off the tank alone I'd say it is a Bridgestone Mach II 200RS chassis. I can't remember the years they made them but it was somewhere in the middle 1960's up until the early 70's. Since it doesn't have the chrome tank I am going to say it's probably a 70's model. AD used to have one when I worked at Vespa. The Amal GP carbs are a big deal - those things are expensive.
http://www.motorcycleclassics.com/c...les/1971-bridgestone-mach-ii-ss-zmwz15jazhurg

The heads are Tabloc and if they are unmodified they have the same compression as stock but have a different squish chamber that gives a little more power. Chances are they are modified. Tabloc was eventually bought out by DG and the radial head design is what you see on radial head RD's from them. As Cyorg mentioned someone poured buckets of cash into this engine.

here is a good site with some specs:
Bridgestone RS200 Roadracer

There have been quite a few 175-200cc b-stone racers throughout the years, they are solid bikes and pretty quick for what they are. Certainly would shame a cb175 just about everywhere. I am a little surprised at the rest of the stock chassis considering the amount of work in that engine. It's too bad he doesn't have the custom chambers that would have been made to support that race engine, I have to imagine they were specific to this engine's output and would be hard to duplicate without trial and error through racing.

The long bracket from the headstock is for a full or 3/4 fairing that the bike must have run at some point. It has rearsets so that's good. The absence of safety wire on the front end and the different tread pattern tire leads me to believe that it wasn't the racing setup - it probably ran something period like 32mm ceriani forks. rear shocks look aftermarket too...if they are as period as the rest of it they could be girlings, konis, SWs, or mulhollands. My guess is koni based on the gold decal on the shock base.

BigAl8295 said:

Does anyone know what we're looking at here? A friend picked it up.

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The frame I think is definitely Bridgestone, the tank too. The engine looks like Bridgestone bottom end, that big alloy lump behind the cylinder for the generator gives it away. BUT the heads are not the Bridgestone 175 or 200. Front hub looks too big for 175 or 200 Bridgestone but might be just the angle of the photo, the front end looks like 350 GTR and not 175/200. Interestingly there's a proper modern Dunlop race tyre on the rear and a lousy TT100 up front.

Currently building a 1968 Bridgestone 175cc for a client to original spec, they are pretty little bikes and can be very quick.

I had a 175 sleeved down to 125 with Mahle race pistons, race prepped crank in a Lyster frame, alloy tank, Ceriani forks and Suzuki Titan front brake with race linings and much lightened everywhere. It was a nice thing. Final version of the bike was 207cc using Suzuki pistons and X7 rods and chucked out 33HP at the rear wheel all thanks to disc valves and delorto carbs, tight squish and proper pipes but always thought the was another 4 or 5 HP in there somewhere. It weighed nothing. Interestingly we created air boxes on the inside of the fairing on each side. I found long bell mouths were a waist of time and so used very short stacks - disc valve engines have a longer intake cycle than piston ported engines.

The main thing to remember with these bikes is keep them light, putting big forks and brakes on will just add weight and if hustle them you'll wrap yourself around a tree. Its all about corner and exit speed; a bit like driving an old diesel van. And if sorted there's very little out there from the late 60's with similar CC that will stay with one of these little gems.

Photos below of 175cc engine c1968, note standard head photo'd to those in the feature photo, cases with the big casting behind the cylinders and another of correct cylinder.