OEC, POST LSR

After a successful career housing a supercharged 994cc JAP engine for several attempts at the Motorcycle Land Speed Record with Joe Wright aboard, the unusual OEC chassis built for the specific purpose of breaking records was host to another blown engine, this time from a car.

The Aug. 30, 1934 edition of 'The Motor Cycle' has a short article on a 'A New Racing "Four"', detailing the attempts by J. Granville Grenfell (what a name!) to create a 500cc machine, with the specific intention of being the first motorcycle to achieve 100mph for an hour, and win a 'Motor Cycle' sponsored trophy for a multi-cylinder/100mph/1hour British motorcycle.  While the OEC was being built, a New Imperial 500cc v-twin took the prize with 'Ginger' Wood the brave rider - it was said he was the only person willing to risk his life aboard the evil-handling New Imp, which spat him off with a tank-slapper at 100mph on the Brooklands banking, while practicing for the record. By comparison, the OEC was a far safer bet at over 100mph; the 'Duplex' steering system being almost too stable at speed, taking some effort to deflect from a straight-line course.  Of the two possibilities, I'd take stable over wobble.

As the raison d'etre of the revised OEC had passed, the Grenfell's (under the sponsorship of Minnie Grenfell, a trials rider) entered the machine in the 'Hutchison 100' race at Brooklands that August of '34.  F.W.S. Clarke was the pilot, although the machine 'failed to distinguish itself' in the races, as the engine was yet 'too tight'...although building a record-breaking engine to 'tight' clearances is dubious. The motor in question is an Austin 7 four-cylinder sidevalver, sleeved down from the original 742cc to 490cc, making a very long stroke indeed at 46mm bore x 76mm stroke.  The crankshaft, notoriously prone to breakage on 'sporting' Austin 7s, was an especially strong one-piece item, yet retained only one main bearing at either end (in '36, Austin introduced a '3-Bearing' crank).  The crank end held a sprocket, presumably between the main bearing and flywheel clutch, which drove a Centric supercharger, mounted above the Morgan 90degree bevel-drive box, which 'turned the corner' and made a rear drive chain possible.  There was no gearbox per se, making the OEC a supercharged four-cylinder single-speed racer!

More technical points on the modified engine: the Centric blower began puffing at 25rpm, giving maximum pressure of 20lbs/sq" at 6000rpm, producing an estimated 46hp 7000rpm...about twice the safe revs of the standard Austin engine, and nearly 3 times the original 17hp.  A sporting Watmough cylinder head gave a better combustion chamber shape, although the compression ratio remained a lowly 4.5:1...not an issue with a supercharger, which needs neither high compression nor radical valve timing to produce maximum power.  In fact, a very tame camshaft with little 'overlap' of valve openings produces the best results with a blower, as it's the job of the compressor is fill the cylinder completely with fuel/air mix, no fancy engine tuning is required, other than the ability to hold the engine bits together, after a dramatic increase in horsepower.

To keep the engine cool, a Scott radiator fits snugly at the front of the engine; hopefully a waterpump was used rather than the 'thermosiphon' system of the Scott, notoriously prone to boiling, although the OEC used glycol rather than water for cooling - a novelty at the time.  The OEC frame was modified to fit all this machinery, and it was estimated the bike would be good for 118mph, and although 'nothing like this speed' was achieved during the 'Hutchison 100', the 60" wheelbase chassis was reported to handle 'extraordinarily well'.

Of course, the OEC wasn't the only motorcycle using an 'Austin 7' engine, as Brough Superior used the engine as well - see the Road Test here.

O.E.C. WORKS RACERS

Any time I see an 'ex-TT Works Racer' coming up for auction, my ears perk up and I start pulling books off the shelf and making phone calls to Australia. It's really rare that any machine claimed to have been built specially by a factory for the TT (1.) comes up for auction and (2.) is genuine, for the simple reason that so few have been built, and even fewer survive the rigors and modifications of racing in the subsequent years. And to be generous, sometimes owners are confused or optimistic that their racing machine was a unique bike created by the factory for a special race.

The ca. 1934 O.E.C. (Osborne Engineering Co.) ex-Works Racer coming up for sale at the MidAmerica Las Vegas auction is a real rarity, from a company which only sporadically competed in the TT at all. OEC is better known for it's 'odd engineering contraptions' than for any racing dominance, yet they periodically threw their hat in the ring at the TT, and in chasing the World Land Speed Record. Their most famous design is a form of hub-center steering (which they called the 'Duplex' system), which was introduced in 1929 to a skeptical public...just like the one today which won't buy Yamahas or Bimotas with hub-center steering!

Little is documented about the mid-30's foray into racing by this tiny company (they only produced around 300 motorcycles/year), but we do know that between 1933 and 1935 they produced perhaps half a dozen machines for the Isle of Man TT, using genuine racing J.A.P. ohv engines of 250cc, 350cc, and 500cc. The '33/'34 engines had aluminum crankcases, whereas the '35 effort used magnesium. Students of motorcycle history will recall that these were dismal years for the JAP racing engine, with lots of failures at the TT, which led to their prestigious client base seeking other engine makers to fill their chassis, notably Brough Superior (who found AMC engines more reliable) and HRD-Vincent (who made their own).

OEC chose to use two types of chassis for the TT; a single machine used the 'Duplex' frame (almost inconceivable given their well-documented tendency to hold and keep a straight line unless muscled over), while the other machines used Webb girders (as seen in the photo above - Freddie Clarke at the '35 Lightweight TT). These Works bikes were the only OEC's to use Webbs, and the particular fork is unique to these bikes, as the steering head on an OEC is considered to be the longest on any motorcycle; something like 9 inches, requiring a new jig at Webb's and a host of one-off links and tubes. An 'OEC' Webb girder won't fit any other motorcycle, so you'll know if you stumble across one.

The back end of the OEC frame is their own version of a swingarm frame, introduced in 1929 (see drawing), which uses a full 'loop' at the back end for stability, and the swinging fork situated between compression and rebound springs housed within the frame tubes. The Works machines also used Harwal wheels (same as the Excelsior Manxman and OK Supreme racers), and special petrol/oil tanks. The auction machine appears to have all the right stuff, although I haven't seen the crucial engine/frame numbers yet. The crankcases look to be correct, but the cylinder barrel is alloy, and the cylinder head looks to be a scantily-finned Speedway item - but in the racing game, everything is up for change in the name of speed.

I've only seen one other OEC Works racer, which turned up at a swap meet in Australia, housing a Suzuki dohc 4 cylinder engine! Yes, the owner is restoring it!

Many thanks to Mitchell Barnes for his information.