c.1957 Norton 500cc Manx Racing Motorcycle
Frame no. 70736
Engine no. 11M76894
The 350 and 500cc Featherbed-framed Manx Norton was available in strictly limited quantities over a 10-year period, arguably becoming the best-remembered over-the-counter racing motorcycle of all time. Norton produced about 100 hand built examples every year, usually just in time for Isle of Man TT practice, where they habitually provided most of the entry, scooping a host of Silver Replicas in both Junior and Senior events. Norton introduced a few improvements each new season and until the factory team withdrew their "works" machines regularly sported the following year's production updates. Despite that the last ever Manx was released c.1962, the Featherbed chassis continued on sale for many years, traditionally acknowledged as the finest handling frame give or take its choice of engine.
The bike offered was treated to an extensive mechanical restoration and sympathetic cosmetic renovation, some years ago, though has been in dry storage since. Built to 1957-58 spec., the bike is not offered in quite race-ready condition but a good running machine. The build began with a stock Manx engine of 1958 vintage, engine number 11M76894. The bead blasted engine cases were the starting point of the rebuild, with a new flywheel assembly, Carrillo rod and Cosworth 11:1 piston. Squish distance is 0.046". New cams were installed; exhaust cam is 5914, and intake is 15822. Intake opens at 67° BT (CL 83°AB) clearance 0.13". Exhaust closes at 38° AT (OP 72° BB), clearance 0.024" all researched through factory sources and correspondence with Ray Petty.
The fully rebuilt engine was fitted to a 1957 frame, number 70736, and then the bike was made up from a number of original parts and NOS sourced items. It has a NOS T5 GP1 Amal carb of 13/8 inch bore with pendant weir-type float bowl, new Reynolds chains front and rear, original wheel hubs, Borrani alloy rims, and Girling shocks. The bike is offered with a 17-25 gear ratio. A couple of departures from standard are a BTH type magneto, and an 8000rpm chronometric tachometer.
A new petrol tank, mudguards, chain guard, fork stanchions, top yoke, engine and transmission mounting bolts, head steady, fairing number cowl, and various other sundry items were sourced from Manx guru Ken McIntosh.
The glaring deviation from Manx racing protocol on the bike offered is the addition of a kickstarter, as the builder/owner of the bike was concerned for, at his years, his ability to bump start the bike. Even with the formidable 11:1 compression ratio, the bike starts well, with the addition of a spark retard lever. However, the original gearbox cover, short lay shaft, and shift mechanism accompany the bike for the buyer intent on originality, or with a greater ability to bump start it.