« on: March 12, 2013, 10:54:14 am »
As most of you know I've got a big love of American flat track bikes and own a couple of two stroke Yamaha examples and have been slowly assembling the parts to build a Trackmaster XS650 and a replica of Gene Hartline's 650 Benelli flat tracker of the late 60's. The latter two projects are now on hold and will probably be sold because I've fallen upon something very special.
I've managed to buy a genuine Shell Thuet OW72 750 Yamaha flat tracker, a bike that's so rare they very hardly ever come up for sale, this is the Dirt Track equivalent of finding an OW motocrosser. The bike was being sold by the widow of a good friend in Las Vegas and although I had no plans for any more bikes until I finished my current projects, this bike shone like a beacon and I just had to have it. A Shell racer with a production based motor recently sold for $9000 at auction and a genuine works OW powered bike sold a couple of years ago for $22000. I paid $3700us for mine in dismantled but fully restored condition. My friend Bob was in the process of assembling the bike when he suddenly died three years ago. The engine has been fully refurbished by a known specialist, the frame re-nickeled, the wheels rebuilt and the bodywork freshly painted in factory Yamaha colours. I've been assured by the seller that all of the major parts are there, the only things not found so far being the seat pad and Grimeca rear brake, hanger and Barnes wheel knock off hardware. There's a possibility that Bob had sent them out for refurbishment and unfortunately died before picking them up.
From what I can find out, the OW72 750 engine shares no parts with it's XS650 production brother. The transmission is close ratio handmade by Webster, the clutch is titanium or magnesium, the crank cases are cast with better material and feature additional internal webbing to handle the big HP, the crank is lighter, Carillo rods and Shells own pistons and camshaft are used and the head is a special casting with different angled inlet tract and different valve angle+bigger ports, the ignition is YZ/OW motocrosser based and a lot more stuff I'm yet to learn.
I'm about to enter into a big a learning curve on these things so once the bike is safely out of the US I'll be contacting those in the know. Unfortunately, the creator of these bikes and the head of the Yamaha flat track team at the time Shell Thuet died a couple of years ago aged 98. Thankfully there are a number of folks who know a bit about OW72 engines so they'll be getting a hammering from me 
The bike has Ceriani forks, Barnes wheels, Shell frame and bodywork, S&W shocks (Shell Thuet was th S in S&W along with Tim Witham. Every Shell has S&W shocks fork springs and valve springs of course) The pipes are 1.75" reverse megaphone tuned length thin wall items and there are no silencers so we'll have to cross the noise bridge when we get to it. As rare as this bike is, it will most definitely be raced in the twins race series and anything else it qualifies for. It's ironic that fellow Klub Kevlar Komrade Fast Eddie Phipps owns the ex Eddie Lawson OW72 Shell, an almost identical bike to mine, the only two OW's outside of the USA that we know of. http://vft.org/Memorial/Shell/ShellThuet.html 
Below: Tom Hortons identical '74 works Shell OW750 
« Last Edit: March 15, 2013, 04:19:33 pm by firko »
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'68 Yamaha DT1 enduro, '69 Yamaha 'DT1 from Hell' '69 DT1'Dunger from Hell, '69 Cheney Yamaha 360, 70 Maico 350 (2 off), '68 Hindall Ducati 250, Hindall RT2MX, Hindall YZ250a , Cycle Factory RT2MX flat tracker, Yamaha 1T250J, Maico 250 trials, '71, Boyd and Stellings TM400, Shell OW72,750 Yamaha
