A performance camshaft known as the Daytona appeared on both engines, while the 99 had an Amal 376 of 1.1/16". A bore and stroke job was also done, the new dimensions being 68 by 82mm to give a capacity of 596cc with a compression ratio of 7.4:1. The year 1956 seemed to be the year of many changes the Model 7 was dropped, but for the 88 a new higher compression cylinder head was brought out giving 7.8:1. The brake horse power became quoted as 29.5 with the limit now taken from 6000 rpm to 7000. The compression ratio was now 6.8:1 and the carburettor an Amal 376, still of 1" bore. The new frame was claimed to be some 30 pounds lighter though there doesn't seem to have been any corresponding improvement in top speed, but acceleration was better.Īn alloy cylinder head was fitted to the Model 88 although it had been first used experimentally in 1950 on the ISDT works twins. The first few years saw the engine in the single down tube frame, but in 1952 it was rehoused in the new Featherbed frame and it thus became known as the Model 88, though this was not marked by any significant changes to the engine. The layout of just about every part of this engine was to remain unaltered right through to the end in 1976, camshaft bushes, drive chain and half time gear, oil pump, main bearings, drive side roller and timing side ball race, three piece crank, handed pistons, rockers and their shafts can all be readily recognised for their origins even if detail changes render the parts not directly interchangeable. The cast in carburettor manifold was soon replaced by an alloy bolt on unit. The top speed of the new bike was 92 mph, which was quite good for the day, along with a fuel consumption figure of over 50 mpg even if driven hard. The machine was first seen at the 1948 Earls Court Show and given the designation Dominator Model 7. Ignition was courtesy of the ubiquitous Joe Lucas magneto. The cylinder head was of cast iron with an integral single carburettor manifold and equipped with a 1" Type 76 Amal carburettor. Both inlet and exhaust valves were of the same size at 1.29", compression ratio was 6.7:1. The original capacity of 497cc was achieved by a bore and stroke of 66 x 72.6mm. Old machine tools and old ideas stopped him from producing a one piece crankshaft so a strong three part one was designed with careful attention to detail so as not to copy the Triumph crank. The former was overcome on the new engine by incorporating splayed exhaust ports so allowing more air flow over the particularly hot areas, while the rattling was supposedly reduced by the use of a single camshaft driven by a chain. I hope in these few notes to cover part of the history of the Norton marque, but this time only dealing with the twin cylinder engine and its production changes.īert Hopwood left Triumph in 1947 in order to join Norton as Chief Designer and the opportunity to design his own vertical twin engine without the drawbacks of the Triumph, i.e. in production forms, A third place in the 1961 Senior TT, first in the 1973 Formula 750 TT and 139 mph as a dragster are just some of the feats this engine has achieved and it has also been the basis of some twenty models of Norton through to the last Commando. The basic span of the humble 500cc to 828cc Norton twin engine design was from 1947 to 1976.
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