Andover Norton Bikes

The „Commando Tripple“ alias „Jake“ was rebuilt around an engine I found in the spares stores of Norton Motors (1978) Ltd in the early 1980s, when visiting there as, at the time, Germany’s biggest Norton spares distributor. It was just a couple of cardboard boxes with dirty engine parts which I initially mistook to be a dismantled standard production Commando engine. Little was known about it at Norton Motors (1978) Ltd but that it had been a complete motorcycle originally, sold by the factory at one time, and bought back for some reason. It was then dismantled and the engine put into a corner.
Richard Negus, then the Spares Manager, sold it to me on behalf of Norton Motors (1978) Ltd.

25 years later that very Richard Negus, as a farewell present to me on retiring from our jointly owned company Norton Motors Ltd, rebuilt the engine and mounted it rigidly in a Commando chassis I had bought and restored for it.

On the right is the drawing how Doug Hele, who had the idea to put a balancing device on a parallel twin, designed the prinziple originally. I found the drawings in “British Motorcycles” by Steve Wilson. Wilson writes:
"Hele’s balancer linkage design for smoothing out 360° parallel twin vibes, with two extra conrods going out horizontally to two smaller links which pivot about their “small ends."

Hardly a quarter of a century later Ducati re-„invented“ exactly that principle, and put it into their „Supermono“ racer, and today it can be found in the BMW F800 engines.

The NVT works R&D department tested the principle, first using a 750 Triumph Twin engine. Under Norman Hyde’s supervision, with Jack Shemans doing the wrenching, they used Hele’s experimental solution, providing an extra piston, rod and a cylinder, at 90° to the working cylinders.

Later that very crankshaft from the Triumph engine was put into a Commando engine. Until I found the technical drawings in our (Andover Norton’s) files it was a complete mystery to me why they did it. The stroke was too short, the Triumph having only 82mm against the Norton stroke of 89mm, so Shemans put high compression pistons in the engine to get some compression. He also- I suspect because he did not fully understand the Commando engine- blanked off the very efficient breather behind the “ear” of the crankcase and let the engine breathe via the left hand main bearing into the primary chaincase, Triumph style. He also steel-sleeved the inlet ports down from 32mm to 30mm, probably because nobody told him 850 heads with 30mm inlets existed off the shelf, and did his usual spiel on the valve guides, slimming them down and cutting them back, racer style.

Compression is still on the low side, and, probably because the moving masses are so heavy- steel conrod and piston in the balancer- the bike does not really want to rev much over 5000 rpm.

I wondered for many years: Why did they take the trouble to build that crank into a Commando engine?
They changed fundamental criteria in that the stroke and cylinder head were totally non-standard and, normally, when one tests one particular modification one leaves all other components standard.
From their test rides with the Triumph they must have known the system works- so why take the trouble to put it into a Commando?

Now that I have seen the engineering drawings I know why they did it, and that we made a fundamental error when we rebuilt that motorcycle. We mounted the engine rigidly in the frame, which works, because vibration is nearly gone, assuming this was how it was tested.

It also makes the bike probably the best-handling Commando I ever rode, with hairline steering that I rate better even than that of my featherbed Manx.

However, in the drawings I saw they mounted that engine IN ISOLASTICS, probably to get rid of the vibrations one still feels in low revs, even though they are not significant. This would explain why they built a Commando with that crankshaft, which otherwise was pretty pointless.

Naturally, I found the drawings three years after the bike was finished and after I found it rather pleasant to ride. I am not sure yet if I want to take the trouble to rebuild it to the factory experimental specification!

One other special feature of the engine is the timing cover, which appears to be a pre-production prototype of the Mk3 timing cover with the oil non-return valve. This puts it into the 1973/74 era. The balancer conrod drawing is dated Sept.73 (On Triumph/BSA paper), all the Norton drawings are undated, which is unusual, but on Norton/Wolverhampton drawing paper.