Alpha Disc Valve Engines

Alpha Centuri
	I believe that there were seven complete Alpha Centuri twin cylinder engines built, and maybe two or three single cylinder development engines built (five crankcases were cast). I also believe that three complete twin cylinder bikes were built, one was written off in a crash, two bikes survive, plus additional engine bits, and that bits for three single cylinder units exist. My own single cylinder bits were found in an auto jumble in 1998, and the engine is slowly being rebuilt, and will be rebuilt to be paraded and hopefully will show a fair turn of speed, using one of my own methanol VMCC racing barrels and a Susuki piston. Another 250 single is being rebuilt with a Parkinson period barrel, just as the originals were back in the 1960's. This photo was taken in 2003 outside of the Motorcycle Museum near Birmingham), and they don't come much prettier than this.
	It is with much regret that the fire at the Museum 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.

Thanks to Mike Cutler for his time and assistance, he provided some period photographs, Thanks to Mick Walker for permission to use information on the Alpha Centuri twin from his book British Racing Motorcycles (ISBN 0-9531311-0-6). 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.

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!

What variations were there?

	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

When did it all happen?

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 Dell'Orto 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 perectly 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 Warfindale had scored three straight wins from three starts on the DMW frame. Don Warfindale and Dave Browning had some good success with the Alpha frame. 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 (below) Mike Cutler

What will my rebuild look like?

Well, something like this. Just a mockup of course. To be mounted in an early Greeves chassis

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.

		Frame ... engine ...
		... and gearbox. What more do you need?

Selection of period photos of the Centuri

What of the Hadley Starr

		The Hadley Starr as it is was, and is today .....
		... the owner may restore it and join me to parade these interesting bikes

A Brief History of Alpha

	Alpha came to the forefront as two-stroke performance equipment manufacturers, duing the late fifties and early sixties, which coincided the begining 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 carburettor. 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 carburettors 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 massive 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 choise of the somewhat suspect Albion HG 5 gearbox was purely political, as Alpha was part of th 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 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 competetive 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 purchaced 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 handfull 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 recieving 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 purchaced, 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 Dell'Orto carburettor, 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 riden 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

Alpha Centuri rebuild