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(Above) A balancer shaft fits between the RZ500's tandem crankshafts; the six-speed transmission plugs into a
cavity below the cranks. (Below) The right side of the engine shows the crank gears, both of which drive the clutch.
By Fraser Stronach
Six years ago a 440-pound roadster developing 84 bhp at the
crankshaft, with 67 bhp at the
rear wheel, would have been un-
IriSIDE 'liE RZ500
2oWho
two-strokEs
arE
simPlE?
thought of. But in the RZSOO this is
now a reality.
Yamaha, in copying its own 500cc
GP contender, has produced what is
for many people the ultimate toy.
Mind you, in the evolution from
racer to roadster the tandem crank
V-4 two-stroke has gained some 40%
extra weight and lost more than a
third of its power - but that doesn't
detract from its unique qualities.
While the basic engine design of
the RZSoo follows the pattern of the
works machine ridden by Kenny
Roberts in the 198!! World 500 RoadRacing Championship and that of
'84 title chaser Eddie Lawson, it is
certainly not a new design.
Yarrtaha campaigned a 250cc tandem crank V-4 as early as 1965, while
Suzuki used a tandem crank square
four 250 some two years earlier.
Many other manufacturers experimented with the same basic design,
among them the low budget Jawa
factory, which campaigned a !l50cc
example as early as 1967.
The term "tandem crank" refers to
the fact tha t the RZSoo has two separate crankshafts. These lie close to one
on top of the other with the lower
crank slightly forward of the upper
crank, so in many respects the RZ500
can be considered as a pair of 250cc
parallel twins geared to a common
dutch/gearbox. Its more common
designation as a V-4 refers to the fact
that the two pairs of cylinders are
displaced some 50° from one another
with the bottom pair of cylinders
