Unit Construction
WHAT IT MEANS TO YOU
The basic principle of Unit-Construction is the casting of the Engine Crankcase and the Gear Box body in one piece, and with it is associated the practice of using helical gear wheels to take the primary drive (i.e.. engine to gear box), instead of the conventional chain- cum-sprockets.
Unless Unit-Construction had some very real and definite advantages, "NEW IMPERIAL MOTORS" would not have advocated, developed and marketed such designs for so many years, but, like a wise man. you want to know just what these advantages are before you purchase.
HERE THEY ARE
In the case of a separate engine and gear box rigidity between the two units is essential if a smooth drive is to be obtained and if the chain is to run in line, at the proper tension. To produce these conditions the use of heavy brackets, etc., is essential and is complicated by the fact that provision for taking up chain stretch or wear has to be made, and at the same time an oil bath case or cover has to be fitted, allowing for the movement referred to above between tho two units.
In the case of UNIT-CONSTRUCTION, however, these difficulties do not arise because :—
(a) The two units are built in one strong casting.
(b) There is no primary chain to stretch or sprocket to wear—only two long-life, robust helical gear wheels.
(c) There is no stretch or wear to take up, and, therefore, no provision for relative movement (between engine and gear box) is necessary.
In the case of separate units chain wear must and does occur, and to take up this " slack " it is sometimes necessary to remove the chain cover to " feel " for corrected slack, to slack off gear box retaining bolts, operate gear box adjusting screw, tighten up gear box retaining bolts, adjust rear wheel position to take up slack in the rear chain created by moving the gear box.
UNIT-CONSTRUCTION renders these adjustments absolutely unnecessary. Save your money on chain replacements — your TIME matters, too !
The helical gear wheels run in an oil bath gear case, the oil supply, quite unconnected with the engine oil circuit, is maintained through a large filler hole. A level plug is provided.
The great rigidity of UNIT-CONSTRUCTION and the use of helical gear wheels in place of chain and sprockets allows the power of the engine to be transmitted to the gear box with A MINIMUM OF FRICTIONAL OR WHIP LOSSES — more M.P.G., and M.P.H, for you to use.
A. R. FOSTER RIDING A "NEW IMPERIAL" 250 c.c. UNIT CONSTRUCTION MODEL WON THE LIGHTWEIGHT T.T. RACE, 1936, AT RECORD SPEED OF 74-28 M.P.H.
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