1 September 2020

Alpha Disc Valve Engines

The Hadley Starr 125cc engine

The Alpha Centuri and Hadley Starr engines have been on loan to me following the ill health of the current owner. The Hadley Starr has been rebuilt and has been running, but needs further work to make it 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.

Hadley starr 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 con rod 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.

Lawrie Watt sectional drawing Hadley starr
He had no immediate plans to market it - Let us see how it goes , first he 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. Hadley 2012
The Hadley Starr in the Autumn of 2011
Hadley 2012Hadley 2012Hadley 2012

Hadley engine on bench Well, what of the future?
Good Question!
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.
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.

Below, Spring 2013 ...

Status since 2013 ...
The photo above shows the Hadley-Starr on the rolling road. Testing did not go well. It started well enough but then the motor just stopped firing and coasted to a halt. On inspection, we saw that the disc-valve was no longer turning with the crank. OK ok, engine out and see what went wrong. Reengineer the location and locking mechanism of the disc-valve, reset valve timing, put gearbox back on and put engine back in chassis. Back to rolling road for retest. Runs well enough, but the DelOrto carb is well worn and it kills the plug if it is run for more than five minutes without load. Under load on the rolling road it is fine, and when it has got rid of the rich starting mixture and on load, keep her lit and 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)

2018 Back with owner, I am hoping that a surface discharge sparking plug will solve the onload running problem,
so that it can be started and run on a paddock stand and displayed at events