Last update January 2019
|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, riden 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 - my rebuild bike was there! The program show lots of familiar names.
Fred Launchbury, Dave Browning, Don Warfindale (Hadley Starr), Derek Chatterton, Dave Croxford, Denis Trollope, and Chas Mortimer.
Lightweight 250 heat 1:
Dave Browning on an Alpha Centuri. Heat 2: Derek Chatterton, Don Warfindale (Alpha Centuri).
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 dont 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! The data on the prototype Alpha 250 singles has been gleaned and scrounged along the way from any source I can find, including an interview with Fred Hadley.
All errors and omissions are my fault, please correct me if you know different. Contact me through Villiers.info
Until 1998 this single cylinder engine drawing (above) was all that I had ever seen of such an engine. The drawing is for the Mk2 single cylinder but before that came the Mk1. It was created by welding on an inlet stub to the right hand crankcase and the right-hand crank flywheel was sculptured to function as a simple disc-valve. Below is a period shot of the Mk1, accompanied by 2003 photos of how the bits have survived.
|See how the flywheel is sculptured to act as a disc valve|
|The bottom half of the engine No. 2 was recovered. I am told that some week previously that the barrel had been with it, and I guess that someone thought it was a Merlin barrel and bought it. Such barrels are quite distinctive of course, as they are 2-stroke barrels without an inlet port. I know that someone Up There must want to see it run again, as shortly afterwards I was able to locate a square finned barrel casting which had not had its inlet port machined into it. The bottom half of the engine was left to soak in a tub of diesel for six months, and then dismantled. As you would expect, the shafts and the big-end pin were too corroded for use.|
|The dismantled assembly was taken to Alpha Bearings for review and confirmation that it was indeed a long lost object of desire and in need of tender loving care. Alpha Bearings of Dudley have manufactured some new shafts, and fitted a new big end and con rod assembly. The timing side shaft has been made to accommodate an electronic ignition rotor, and the con rod assembly is a Maico scrambles component complete with silver cage. Tender loving care will be given in abundance, until it gets to the track that is!|
|I can see two variants. My casting (on the left) is all alloy, whereas the crankcase casting on the right has a steel insert to face the inlet port. Whether by design or to rectify wear I cannot say.|
|Period picture of Bob Curry on a MK2 engine mounted in a Royal Enfield frame (borrowed from Motorcycle 1964). This bike was normally ridden by Peter Cutler. It was the second MK2 engine as Mike Cutler already has a MK2 engine mounted in a Greeves chassis. My own Mk2 rebuild will be in my Greeves Hawkestone VMCC chassis|
the gas tended to bounce off the flywheel rims and build up back pressure.
The design of the Centuri twin was laid down in 1962, and the prototype was constructed using Velocette Viceroy scooter barrels and BSA Bantam heads, and was mounted in a DMW frame. Frank Cutler, the designer, was constrained to use the Albion HG5 gearbox since they were part of the EHP SMith Group. It was mounted in a DMW Hornet chassis, and the handling was "interesting" according to Mike Cutler who road it for the next few years. The engine was a 180 degree twin using the then almost standard 54mm x 54mm to give a 250cc twin. Carburation was by 29mm DellOrto SS1 through inboard discs so that the single carb fed both cylinders. The porting arrangements were very similar to the Yamaha TD2 racers that appeared almost five years later, smaller additional transfer ports to direct mixture over the piston crown, for scavenging and cooling. The race version , tuned by Fred Hadley, appeared in 1964 without much success. Royal Enfield who were part of the same EH Smith group, complained that Alpha were using a DMW frame when they have a perfectly good GP5 frame available, and the union was not a good one. The engine was too far back in the frame, so a purpose built frame was made. Don Wolfindale had scored three straight wins from three starts on the DMW frame. A second frame, identical to the first, was made, Don Wolfindale and Dave Browning had some good success with the Alpha frames. Dave Browning became the 1968 ACU Clubmans Champion riding several rounds on his Alpha Centuri. The Alpha Centuri feratured in the rebuild is that 1968 championship machine. A Centuri MK2 engine was loaned to Fred Launchbury for the 1967 TT and he was clocked at 122 mph, just 2 mph down on the works Kawasaki. With the demise of the Royal Enfield race shop, and the acquisition of their dynamometer now installed at Graham Starr Engineering, further development was possible. John Kirkby had many successes using the only privately purchased Alpha Centuri engine in a Ducati frame. The earlier Centuri engines had four transfer ports (42 bhp at 10,000 rpm), and the later MK2 engine had five ports (works motors courtesy of Fred Hadley had 48 bhp at 12,500 rpm, power band 7000 to 10000, production motors had 36 bhp) but primary chains were quickly destroyed and needed to be changed after every race.
A preliminary batch of 25 engines were scheduled for the 1968 season, and a portion of the works canteen was cordoned off to create a "production line". Parts were made and seven engines were assembled, three of these went to DMW and four stayed with Alpha. The engines were intended for sale to customers to fit into their own machines, at a cost of 200 sterling. The project was cancelled at the end of 1968. EHP Smith even reclaimed the engine sold to John Kirkby. The next year Yamaha came through with an engine that was not quite as good and cleaned up commercially. Fred Hadley was not prepared to stop quite yet, and used some of the Centuri parts to make a 125cc single in association with the kart specialists Graham Starr Engineering of Wolverhampton. Using the five transfer port barrel, the Hadley Starr produced 28 bhp at 12,000 rpm with a power band less than 2000 rpm wide. You need better than a 5-speed Albion gearbox to get the best out of a small power band. Frank Cutler had planned to solve the power and transmission difficulties, he had designed a water-cooled geared-primary six-speed disc-valve twin. It was on the drawing board, ready to go.
Copyright: John Wood 2003, period photos of Centuri: Mike Cutler
|Well, something like this. Just a mockup of course. Was to be mounted in an early Greeves chassis, but has been sold on to someone with the correct DMW chassis for a rebuild as it was.|
Alpha came to the forefront as two-stroke performance equipment manufacturers, during the late fifties and early sixties, which coincided the beginning of the
Villiers 197 9E becoming popular as a competition engine. As the power outputs of the 9E increased, so did the failure rate of its standard components.
The advent of the high performance alloy cylinders - and 250 cc conversions - put so much pressure on the standard crank, that it cried enough far too regularly.
Villiers were adamant that there was nothing wrong with their design, and refused to believe that anyone was actually racing one of their commuter engines.
Frank Cutler, then managing director of Alpha, decided to make good the basic inadequacies, a job that should have been tackled by the makers. First item to come out of the factory was the Mk 1 full circle crank and streamlined con rod, but replacement rods for the standard Villiers crank had been available for some time. Villiers used a 0.8 inch crank pin with 26 crowded rollers in the standard road engine, but reduced this to 9 caged rollers in the sport engine. Alpha reduced this even further, using 8 rollers in a better cage for their replacement rod. The Mk 1 full circle crank increased the crank pin diameter to 0.925 inch and hence increased the rigidity of the whole crank assembly. The benefits of the new crank were two fold, its increased rigidity improved reliability, and the full circle flywheels increased the primary compression ratio aiding cylinder filling.
|Next to appear was the Mk 2 full circle crank which had gone metric. The crank pin was now stepped, 22 mm flywheel fitments and a 25 mm bearing inner track. The outer bearing track became 32 mm at 16 mm wide instead of the earlier 0.5 inch wide type. This type of crankshaft was adopted by all the works teams of the day, as it meant that even more power could be extracted from their motors, without the reliability fears of the earlier days.|
|Power outputs continued to creep higher, and this then began to put the pressure on the flimsy Villiers crankcases, the principle problem areas becoming the main bearing housings. To combat this new problem, Alpha then turned their attention to the crankcase castings, coming up with a heavily finned pair that were beefed up in the appropriate places. Instead of the standard two ball and one roller main bearings, Alpha opted for the use of one ball and two roller bearings. The rollers (a single row on the driving side next to the ball and a double row on the timing side) ran in hardened sleeves in the cases, but directly onto the crank drive shafts. As the crank was factory balanced the heavy brass magneto was not required, nor was there any room for it, as the contact breaker ran straight onto a cam ground on the shaft end. The cases were intended solely for racing use, and the use of a total loss battery coil ignition system was deemed to be the most reliable method of generating sparks.|
|Not content with making replacement parts, Frank Cutler turned his attention to a complete motor. The first engine was based on the Alpha bottom end, and in an attempt to provide a better induction cycle, used a rotary valve. The inlet port was positioned on the right hand crankcase at the front, with a machined cutaway on the ultra close fitting crankshaft, acting as the valve. This engine was soon replaced by a Mk 2 version, which placed the induction tract at the rear of the cases. The crankshaft again acted as the valve, but this time the cutaways were machined on the circumference of both flywheels, being fed by a bifurcated inlet tract. A third transfer port was added to the rear of the cylinder, which connected to the underside of the piston, in the redundant area vacated due to the repositioning of the inlet port. The single failed to come up to expectations, in that it would not rev to the expected rpm, even though both Royal Enfield and Scorpion showed an interest in it for their production racer projects. Was it due to the failure to produce the required power, or the demise of the two racer projects that persuaded Frank Cutler to drop the single in favour of a twin.|
|The twin (called the Centuri) used a bore and stroke of 54 X 54 mm, with a pressed up crank that used a pair of inboard discs to collect the mixture from a centrally mounted single carburetor. As the disc controlled inlet periods of less than 180 degrees, this system was deemed as perfectly satisfactory for the state of tune prevailing some thirty years ago. With modern high performance engines having an inlet period of truly wild proportions, this system would not be adequate, and a change to twin carburetors would have been required. Conventional ball races supported the centre of the full circle crank, with caged rollers being used on the outer ends, again running in steel sleeves but directly on the crank drive shafts. A new set of cylinders were sand cast (the development cylinders coming from a Velocette Viceroy scooter) and fitted with spun cast iron liners. The new liners featured not only the main transfer ports but an extra pair of auxiliary ports, placed between the main transfers and the exhaust port. This method of gaining an increase in gas transfer was a full five years ahead of Japanese two-stroke wizards Yamaha, who adopted the same idea for the TD2 racers of 1969.|
|The rest of the engine was quite conventional, except for the star burst cylinder head finning, which replaced the Bantam cylinder heads used for the initial development. Using battery coil ignition and an Albion HG 5 speed gearbox, the motor revved well over 10,000 rpm and produced an excellent power curve. The choice of the somewhat suspect Albion HG 5 gearbox was purely political, as Alpha was part of the E & HP Smith empire who owned Albion. The gearbox was soon changed when Albion came up with their new barrel-cam 5 speed box.|
To test and develop the new motor it was installed into a DMW roadster chassis (the old Mk 1 Hornet that originally housed the disc valve single engine) and given 1000 miles of everyday running to see if it would break, but nothing went wrong, and the engine test ended satisfactorily. Road testing was in the hands of Mike Cutler (Franks son) who described the test as the most fun he ever had. This transpired to mean that although the engine power delivery characteristics were as predicted, the handling and road holding of the DMW chassis was not, which produced a fast but evil handling monster.
The first engine was reinstalled in a Royal Enfield GP5 frame (grudgingly supplied by RE on the orders of E & HP Smith) and called the Centuri, and further development carried out. The frame was supplied on the understanding that it was to remain standard, which prevented Alpha from placing the power unit in the optimum position. The result of this ruling was that the engine was placed too far back, to enable the twin expansion chambers to clear the duplex front down tubes. Handling suffered, with Mike Cutler going as far as to say that the handling was not even up to the DMW frame standards. The Centuri power output was gradually increased to some 48 bhp, but in this form it became fragile, and the output was lowered to 44 bhp in order to make it more reliable. The increases came from the use of a new set of seven port cylinders, a bridged exhaust, four transfers and an extra transfer through the piston. The production engines that would have been on sale to the general public, had the project carried on, only gave 36 bhp, which was enough to be competitive against its nearest rival, the 32 bhp Greeves Silverstone. When asked what the difference was between the production and the works engines, Mike Cutler answered "Fred Hadley and his files".
Testing was carried out on the dyno that RE used to develop their single cylinder GP5, Frank Cutler having purchased it, on the demise of RE. The dyno was installed locally at Graham Star Engineering, (a kart specialist) because of the noise restrictions that prevailed at the Alpha factory, and it was from here that most of the development work was carried on. Later Alpha produced their own frame and used Ceriani forks, for the production run. The run was very small with only a handful of machines being produced. Figures indicate that only eight Centuri engines were built, with enough spares to complete a further 25 units. The only paying customers for the Centuri were DMW, and John Kirkby a leading Cadwell Park specialist, who installed his engine in an ex Tom Phillips/Vic Camp Ducati Mach 1 frame. The Alpha Ducati gaining a couple of wins in its first race despite being over geared and not fitted with a rev counter. Promise was shown by the Kirkby machine, as was with the factory DMW framed machine of works riders Don Wolfindale and Dave Browning, but alas nothing was to come of this forward thinking project.
Alpha finally abandoned the Centuri altogether and went back to making crankshafts and connecting rods for the run of the mill motorcycle market, after receiving an edict from E & HP Smith in 1968, which put a stop to, what Smiths called, costly race development. All the work put into the Centuri (much of it being after hours at a reduced cost and well below budget) was lost, for the ruling stated that "No further engines or spares were to be sold". Even the engine sold to privateer John Kirkby was re purchased, thus Great Britain was deprived of yet another project that could have blossomed, or at least kept abreast with the rapidly improving Japanese hardware. The sad fact is that when the Centuri project was wound up, Frank Cutler had already completed the drawings for a water cooled, gear driven primary, six speed, disc valve twin that would have beaten the TZ Yamahas into production by several years. Frank Cutler even had ideas of a four cylinder 500, but that is another story.
Another project that did blossom from the ashes of the Centuri when it was terminated on the orders of the Smith group, was the Hadley Starr 125. Built by Fred Hadley (an unpaid helper on the Alpha Centuri) the 125 was half a Centuri engine with a side mounted 28 mm DellOrto carburetor, which had began to show some promise. Frank Hadley decided to build the Starr from the vast stock of redundant Centuri parts which then lay unloved and unwanted at the Alpha factory. Using a seven port cylinder with even wilder porting, the single gave an amazing 28 bhp at 12,000 rpm, but at the expense of an 1800 rpm power band, which was not helped by the use of the Albion gearbox. The engine was installed in a frame made by Graham Starr Engineering and ridden by Don Wolfindale, but it proved to be fast but fragile and let down by the gearbox which was full of false neutrals. The Smiths "no racing" ruling effectively put an end to the Centuri and its innovative junior offspring, and any hopes of a racing success.
Copyright: words Rob Carrick 1996, colour photos John Wood 2003
Apart from the pristine example in the Motorcycle Museum, what else has survived? Enough to build another, that is for sure.
run sweet, and is nowhere near ready for the track.
If you missed the Alan Cathcart essay and track test on a pair of Alpha derived disc-valve racers in 1982, regrettable but understandable, then I am about to set the record straight. This section is about the Hadley Starr 125cc racer, inspired by the earlier Alpha Centuri twin, created by Fred Hadley and Graham Starr in 1968, and raced by Alpha works rider Don Wolfindale.
|An original period shot of the Hadley Starr with its elder cousin, the Alpha Centuri.
At the time of the 1982 article in Classic Bike (September 1982) the bike had been out of site for a
decade and more. Alan Cathcart did a back-to-back test at Donington Park between the Hadley Starr and the Alpha Centuri.
The bike could be seen occasionally at classic CMRC events under a special interest dispensation as the bike was
actually finished in 1969, past the club's two-stroke cut-off date. The bike then faded from view once again, this time
for thirty years.
The rebuilding of the bike from 2012, the rebuild photos, and this essay will do something to redress that.
The period photo below shows Don Wolfindale, Fred Hadley, and Graham Starr, and is almost certainly 1969. The trigger for the project was the cessation of racing by Alpha as ordered by E & HP Smith Industries in 1968 (and the story of that is within the essay on the Alpha Centuri). All the work in developing the Alpha Centuri was wasted, but Fred Hadley was able to organise the transfer of dynamometer, castings and patterns to Graham Starr Engineering in Wolverhampton. Motor Cycle reported on the venture and the article was illustrated by a typical Lawrie Watt sectional drawing.
The parentage of the unit is readily recognisable, for it is basically one half of a 247cc Alpha Centuri twin. Indeed, piston conrod cylinder-barrel and head castings are those of the Centuri, though the porting is much modified to obtain maximum power at 10,800 rpm. However, though Fred is making use of Alpha development experience and facilities provided by the Alpha factory, the engine is his own independent venture.
He had no immediate plans to market it -
Let us see how it goes , firsthe says. However, at least two companies have expressed interest in the project and , eventually, a 124cc Hadley production racer is a possibility. For the present, however, the prototype will provide Alpha development rider Don Wolfindale with a ride in an additional class. The machine is an all British project, right down to the contact-breaker assembly. Initially the drive will be taken through a five-speed Albion gearbox though a six-speed Villiers gearbox may be substituted later when this becomes available. The frame design by Hadley himself is generally similar to that employed for the factory Alpha Centuri.
Port design is interesting, for there are no fewer than five transfer ports, of these, the two smaller side ports and the front ports serve to direct cool incoming mixture across the piston. the exhaust port has a bridge, and the exhaust pipe is taken from the rear of the cylinder barrel.Crankcase castings are taken from suitably modified versions of those used for the DMW Hornet engine, and Hadley acknowledges the help he has had from DMW in this connection. the crankshaft design, he says, has been influenced by his association with Frank Cutler of Alpha. The inlet valve disc is 0.020" shim-steel driven as with the Alpha Centuri by a hexagon keyed to the right-hand engine shaft. Ignition is by the George Elliot transistor system, and the carburetor is an Amal Concentric mounted outboard of the disc-valve cover on the right.
How much power? Fred isn't saying.
I know what I am hoping for, he comments,
and since I now have private dynamometer facilities you can be pretty sure that when it does reach the track, it will be competitive.
|The Classic Bike article of 1982 we told that the engine produced 28 bhp at 12,000 rpm using a 28mm DellOrto carburetor. More details were available about the porting: the seven port configuration was developed by Fred Hadley for the Dave Browning "works" Alpha Centuri machine which gave it an additional 6 bhp over the standard Alpha Centuri. It had a very typical and short 1960's expansion chamber, a very narrow power band, and a five speed gearbox with more neutrals than you could shake a stick at. The later cam-barrel five speed Albion box which is now fitted should be a big improvement. The bridged exhaust port, and the porting generally is very reminiscent of the classic Upton 60mm barrels that are used by the Villiers 210 Challenge goKarts today. In total, seven of these Hadley Starr racers were built before competition regulations were altered to favour the multicylinder Honda. Now the focus became the 100cc goKart specification, and the prototype was tested in 1970, the debut Starr SS100 gokart driven by one Nigel Mansell who set the fastest time of the day.|
The Hadley Starr in the Autumn of 2011
|Well, what of the future?|
The photo here is Spring 2012 and the motor has been stripped and checked, the verdict is "not too bad" and I have rebuilt it amending problems so that it is safe to run and parade, but it still have its 1960's exhaust and points ignition. It would be splendid to have Alan Cathcart ride it again, but not a chance until it is running on electronic ignition. In the fullness of time it will have a 1980's exhaust and a decent ignition. but only after the Alpha Centuri engines are finished. That is correct, I have spares for two engines. The story and pictures of those are unfolding in another essay. One will be for parading and be a period engine, the other will have the seven port barrels and modern internals, and be encouraged to race.
|OK, so lets start with the problems.|
|OH Really? you thought that there would be no problems?
The left two photos show how close the engine and gearbox are. They are so close that the outer disc-valve cover is cut away and the inner gearbox cover on the cam-barrel Albion box is almost filed paper thin, so the engine and gearbox will *not* go any closer. But the frame mounting dictate that they cannot go any farther apart. So much for primary chain adjustment!
The next photo shows the crankcases, and after aqua-blasting the araldite on the transfer cutouts is falling out. This has been repaired with DevCon.
The final and rightmost photo shows the primary drive. the clutch is so close to the stud that I cannot fit the outer chaincase without modification. The engine sprocket is non-standard, not the Greeves 21 tooth sprocket as expected, and as explained above I cannot move the clutch position. See the very nice unbreakable duplex chain from Nametab Engineering.
On the left, the crank pretty much as it was when engine was stripped. Then the timing side case with devcon filler in place but not yet smoothed to shape, and finally the view of the barrel and crankcase mated to allow the devcon to be correctly shaped using Swiss files.
On the left, the Hadley barrel, note that the exhaust stub is bolted on, whereas the Lawrie Watt drawing is of the later goKart barrel having a cast-in stub. Next, setting up and making the spacers to support the disc-valve on its keyed hexagon drive, then the engine inverted so that I can check the operation.
|These photos really underline the difference in British and Japanese two-strokes regarding transfer porting. On the left is the
Hadley Starr barrel, in the centre is the Alpha Centuri 5 port barrel, and on the right is a Yamaha TD3.
And below, is a picture of the production Starr SS100 kart engine.
keep her litand she just sings. Before returning the Hadley-Starr to its owner, it was taken to Wolverhampton and started for a few interested folk, including the daughters of the part creator Graham Starr. They took a video. (75 secs of MP4: Right-click and save-as, play locally)
|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
The crank was refurbished (rather than remanufactured)
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.
|Here are the new crankcases, lightly machined just to get some datum surfaces, in the background are the alloy discs which will become the induction and the disc-valve covers. The original Alpha crankshaft I found quite fiddly so after due measurement I decided to build an Alpha with a Yamaha RD250 crankshaft.|
|Now the crankcases are somewhat machined inside, enough to accept the centre discs, and the through bolt holes. The three centre discs are outline machined so that the crankcases can be bolted up and machined as a unit. This work requires the barrel surface to be created and the barrel liner holes inserted. Then the crankcases are turned over to machine the inlet manifold flange, and bore down to create the induction tract. Finally, the gearbox mounting surface machined and through bolt holes created. This work is in progress.|
|The inboard disc valves are held captive in carriers which are keyed to the crankshaft. Between the two inner crank webs are two carriers with their discs and oil seals plus a centre bearing. So the carriers and the bearing sit inside the main centre induction machining, and two covers encapsulate the disc-valves. These covers have crowded roller bearings and support the carriers to create a five bearing crank. These components are the final test pieces to verify assembly and fit.|
|See here the disc-valve and a carrier sitting against the cover plate with the oil seal in place, against this go the centre bearing and the other carrier. The carriers are marked out with pilot holes by the CNC so that I can control the valve cutouts and vernier location holes with the keyway slot.|
|The disc valves themselves could be easily laser cut but I decided to make them to test my CNC which I am still learning to use. I make four valves from a single A4 sheet of material, which is held and supported by a sandwich of nylon (kitchen cutting block) and some MDF. This makes the basic inner shape and accurately puts the vernier location holes. The circular part of the valve is cut in the lathe using a homemade jig, material is nylon to test jigs and CNC computer program. I subsequently made further discs of carbon fibre and steel.|