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smaller works four cylinder 2 stroke racer,
the YZR500, or OW19, first saw competition in
the 1973 French Grand Prix, won by the late,
great, Jarno Saarinen. The bike had originally
been little more than basically a "double"
TZ250, including a rather large dose of the
250's peakiness, and had been fitted with reed
valve induction to tame it's power delivery
by the factory after the "Flying Finn",
Saarinen, had made comment on the difficulty
he had controlling this type of power surge
from such a potent machine.
From it's initial successful debut the bike
underwent regular changes with each new version,
some changes were advantageous, and others not
so, until the introduction of Yamaha's first
production 500cc racer, the TZ500 G.
The "G" was a piston port four cylinder
racer featuring mechanically operated powervalves
to make it a little more "rider friendly".
These operated by cable from the primary gears.
Unlike the 750, this bike shared little in
common motor-wise with the smaller twins, with
it's entirely new crankcases featuring alternate
( individual ) cylinder barrel bolt pattern
ensuring that no-one could "try out"
a pair of 250 top ends as an experiment!! Internal
gear ratios were able to be changed easily,
with access to the "cassette" style
gear arrangement being available behind the
primary drive cover. The original spares kit
had various different gears to choose from.
Suspension wise, the forks came with air caps
and the rear shock was adjustable for both compression
and rebound damping as well as spring pre-load.
The bike came with the same fork sliders as
the 750 but had different internals. The old
cast iron calipers were mounted to the forks
in the usual way except that the mounting lugs
had the backs cut away to allow quick removal
during wheel changes. The TZ500G was not a brilliant
bike compared to the opposition and was renowned
for gearbox seizures, a no doubt terrifying
Just two more models of TZ500's rolled off
the assembly line following the "G",
they were the "H" and "J".
The J model featured new Nissin front brakes
with new square shaped pads. Brake disc diameter
went up to 320mm from the G and H's 300mm.
the H or J was particularly competitive at World
Championship level, so the factory ceased production
of customer TZ500's in 1982, but has continued
it's long line of works YZR500's right up to
2001 when development for the M1 MotoGP racer
took over in preparation for it's debut season
Ex- Kenny Roberts 1980 OW48 works TZ500
bike featured a 56mm bore, 50.6mm stroke, piston
port induction with electronically controlled
guillotine style exhaust valves, running either
34, 36 or 38mm round or flat slide Mikuni carbs.
It also had provision for variable gear ratios
on the first four speeds.
The frame began initially as a tubular steel
item, later changed to a box section aluminium
unit painted black to "fool" the opposition.
It didn't. It also featured externally adjustable
Front wheel was an 18" diameter by 2½"
wide, rear was 17" with a choice of either
3½ or 4" width.