1 September 2020

Alpha Disc Valve Engines

The Alpha Centuri 250cc twin

The Alpha Centuri 250cc twin

Alpha Centuri before Alpha Centuri after I believe that there were at least five complete Alpha Centuri twin cylinder engines built, two in original Alpha made frames (my bike is #2, ridden to ACU Championship winner by Dave Browning 1968) and three in DMW frames, and maybe two or three single cylinder development engines built (five crankcases were cast). This photo of Alpha Centuri #1 was taken in 2003 outside of the Motorcycle Museum near Birmingham, and they don't come much prettier than this. In addition, a derivative 125cc single cylinder machine was created privately by Fred Hadley in conjunction with Graham Starr named the Hadley Starr. The Hadley Starr story is detailed below, for now we concentrate on the Alpha Centuri 250cc twin. It is with much regret that the fire at the Museum in 2003 destroyed this bike and many others. Mike Cutler gave me his time and arranged that I could take the picture above just a few weeks before the fire.
Castle Coombe 1968 Castle Coombe 1968 - my rebuild bike was there! The program show lots of familiar names.
Lightweight 125: Fred Launchbury, Dave Browning, Don Wolfindale(Alpha), Derek Chatterton, Dave Croxford, Denis Trollope, Chas Mortimer.
Lightweight 250 heat 1: Dave Browning on an Alpha Centuri. Heat 2: Derek Chatterton, Don Wolfindale (Alpha Centuri).
Lightweight 250 Heat 3: Stan Woods, Dave Croxford, Chas Mortimer.
Junior heat 1 : Stan Woods, Dave Croxford, Denis Trollope. Heat 2: Tony Rutter, Derek Chatterton, Malcome Uphill.
Senior heat 1 : Mick Grant, Gordon Pantall. Heat 2: Ditchburn, Croxford, Trollope, Percy Tait
and probably more too whose names I don't recognise

Thanks to Mike Cutler for his time and assistance, he provided some period photographs. Thanks to Fred Hadley for making the time to talk to me, and thanks to the owners of the machinery pictured here for letting me through the door. I even got cups of tea. Cheers lads!

Will we ever parade an Alpha Centuri

Apart from the pristine example in the Motorcycle Museum, what else has survived? Enough to build another, that is for sure.

Alpha3a Alpha3b Alpha3c Alpha3d
Frame ... engine ... and gearbox. What more do you need?

Period photos of the Alpha Centuri

period Alpha Centuri period Alpha Centuri period Alpha Centuri
period Alpha Centuri period Alpha Centuri period Alpha Centuri

Alpha Centuri - status 2013

The Alpha Centuri has two engines, one is mostly original parts excepting only new pistons, the second is tired to say the least, and needs a lot of work. The first will be a parade engine only, and the second needs a total rebuild. The clutch I had been given was just too awful to contemplate, so here is a belt drive version of the CNC copy of the Griffon clutch by Nametab Engineering, fitted to the engine to be paraded. Pistons are Suzuki RG125, disc valves are newly laser cut, all else original.

The Alpha Centuri drawing by Laurie Watts shows the central block, this houses the two inboard disc valves and a central main bearing flanked by oil seals. The inlet apertures which are controlled by the disc valves have become distressed by wear, stones and fatigue. I have inserted an alloy-bronze piece to restore the cutting edge.

The crank was refurbished (rather than remanufactured)

Crank [dis]assembly requires jigs and some patience.

Alpha Centuri - status 2016

The engine is assembled and in frame, with a view to showing this Dave Browning machine at the VMCC/BHR Cadwell Park festival in June 2016.

Photos show complete machine about to be taken to the show, it has been started but not yet subjected to the dyno. The festival picture shows a DMW Centuri in the foreground with further Centuris behind. I doubt that five Alpha Centuri were ever together in one place at anytime in the past.

Alpha Centuri - status 2018

The bike went to the rolling road. The first test was ok but it was obvious that work on the fuel system supply and float bowl action was required.

Testing with a dummy tank is not the best, so I have made an alloy fuel tank. I am not the best alloy welder in the West Midlands. Now with a proper fuel tank, a revised clutch push rod arrangement, weaker clutch springs, and a reworked fuel system, and still with its enormous jets (1400 on petrol is the standard fitment) it did perform much better. The second test is a disaster. Something seized inside the clutch operating mechanism, shortly the adjuster and outer gearbox cover exploded showering bits all over the dyno-house floor. Test ends!

Delay whilst I do repairs shown above. After 10 or 15 mins of gentle running, looking for problems and letting the engine fully warm through, it was given more demands. It runs clean to about 9000 rpm, which was my self imposed limit, until the crank and pistons have had more running time. The carb is dripping all the time. The downdraft of the manifold and the downdraft of the engine conspire to angle the carb at 25 degrees, this is too much.

Alpha Centuri - status 2019

Delay whilst I make an angled induction extension so that the fuel system does not drip, carb is now at 15 degrees downdraft not 25 degrees. A rolling road test is fine with the engine running much cleaner and starts easily, pulling to 9000 rpm (my limit again), but it is over-geared and pulls 105 mph in 3rd but will not pull 4th or 5th well.
Started for a final time in 2019 in a Worcestershire garden to appreciative audience.

The Alpha Centuri is now robbed of its PVL ignition and its belt-drive dry-clutch, the RD-Alpha project needs them, and rebuilt with original oil-bath primary and original fuel tank, and wheeled into its 2019 winter storage.