Classic Cycles Technical Resources
37
C. Gear Shift Operation:
The rotary valve engines are equipped with rotary-type shift mechanisms. Each time the shift pedal is
depressed with the toe, the transmission shifts one gear higher. Starting in neutral, if the pedal were
depressed and released 3 times, the transmission would shift from 1st to 2nd to 3rd to 4th and back to
neutral. Fig. 71. Depressing the rear portion of the pedal with the heel shifts the transmission down one
gear lower each time it is depressed.
The transmission in the 175 Dual Twin can easily be
switched from the rotary change type four speed (described
above) to the return change type five speed with overdrive
(left) by simply moving a sportshift lever. (NOTE: This
sportshift can be moved while in any gear except neutral.)
The gear change system components are installed in the left
crankcase cover so that maintenance, disassembling and
inspection are easy.
Bridgestone 175's manufactured before November, 1965, (Serial No. 16W02913)
were equipped with the old style shift drum on which there were two neutral positions. As illustrated above
right, one neutral was positioned between 1st and 2nd gear, the other between 4th and 5th gears.
Fifth gear B is put into play by putting the "Sportshift" lever in the 5-speed position and depressing the
shift pedal. Turning the lever positions the guide pin in the 5
th
speed shift drum groove, thus connecting
the 5
th
gear shift fork to the shift drum. When the shift pedal is depressed, the drive dogs on 5
th
gear B (a
free spinning gear) engage the drive dogs on the drive shaft, thus transferring power from 5
th
gear A, which
is keyed to the clutch shaft, to the drive shaft.
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