Yamaha
TZ350
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 1973
saw the introduction of the bike which was about
to transform the 350cc GP class worldwide, the
incredible TZ350A. The inclusion of water-cooling
in addition to other slight improvements over
the bike's air cooled predecessors, the TR2,
TR2B and TR3, saw Yamaha's 350cc production
offering fast becoming an almost unbeatable
weapon in the hands of the right rider. Internally
the motor hadn't changed much from the previous
model apart from the widths and angles of the
transfers being altered to improve scavenging,
though actual port timing remained as it was
with the older model. Also the silicon content
of the cylinder was lower compared to that of
the TR3's separate hypereutectic units. The
new bike produced a very respectable 60bhp @9,500rpm.
Interestingly, there was no variable advance
built into the Hitachi TIA02-01 CDI controller
used on the 350. Whatever ignition advance the
tuner set was the advance right through the
rev range. ( This was not the case with the
TZ 250 ).
In 1974, the "B" model was released,
with very few changes to the previous "A".
As if this wasn't frustrating enough, TZ racers
had to sit out 1975, waiting until the next
year for a new version. The wait was worth it....
The "C" model, of 1976 was another
matter entirely. Here was a radical departure
chassis and running gear wise from the earlier
TZ's. Adjustable "mono-shock" (spring
preload and rebound damping only) rear suspension,
combined with twin piston front and rear disk
brakes set the world on fire, with the new bikes
selling like hot-cakes from Yamaha dealers worldwide.
The retail price of around £ 1,550 including
a comprehensive spares kit was incredible value
for money and did no harm at all to sales. The
clutch basket "boss" was improved
by changing it's method of attachment to a male
/ female spline system from the previous model's
"dog" type. The exhaust header picked
up an additional o-ring and a new mounting system.
Power jumped up slightly to 62bhp @ 10,000rpm.
What is essentially a TZ350E on display in the
Macau Museum. This bike has an F model top end,
Lockheed calipers and magnesium wheels. It also
has the gear shift foot lever fitted to the
right hand side of the bike indicating that
possibly a British rider may have raced it at
Macau. (Photo provided by the Macau Museum.)
The "D" and "E" models
of the next two years were a little disappointing
from the "punter's" point of view
due to the fact that very little was altered
at the factory from the "C".
Minor porting, piston and exhaust upgrades
saw the peak horsepower output up by 2 to reach
a claimed 64bhp @10,500rpm. The factory also
chose to fit an offset, angled plug head with
the "D", in an effort to combat cylinder
and piston distortion as well as slightly raising
the compression ratio. New expansion chambers
were now fitted from the factory with removable
silencers. Small changes were also made to items
like the base gasket, crank webs, small end
bearings, the gasket for the side oil draining
bolt on the gearbox, carby floats and choke
systems etc. Tyre widths were also increased
from the factory though rim sizes remained as
per the previous model.
Not to say that the TZ350 became uncompetitive
with the introduction of the "D",
quite the contrary, with customer bikes winning
350cc races and domestic championships across
the non-USA world from 1977 through 1978. (America
didn't run a 350cc class but allowed 350cc bikes
to run in other larger capacity classes.)
The "E" had a new frame which some
say re-positioned the engine slightly more forward
featuring detachable alloy engine plates and
around 20 other additional bolts, nuts, washers
etc. as well. The swing-arm length remained
as for the "D" as did just about everything
else apart from the rear lower engine mounting
bolt which was lengthened by 5mm.
The introduction of the "F" model
in 1979 saw, finally, effective and much anticipated
improvements to the now 3 year old TZ 350 C/D/E.
Much to the relief of Yamaha devotees, the factory
made several changes to the bike, some advantageous,
in time owners learnt others were not. They
included:
- The provision of a new "6 port"
cylinder, with subsequent improvement in rideability,
with an improvement in peak power output to
boot. Also new "cross-over" style
chambers to keep the muffler tips within FIM
requirements length wise and a new piston.
The "F" pistons were the first of
the short pin "slipper" type but
the side windows didn’t have the support
web running down the middle, and the ring
sometimes pulled the edge of the piston down
into the window.
- A new conrod, which was lighter, but turned
out to be prone to failure ( due mainly legend
has it, to the wrong silicon content in the
pistons causing them to wear and deposit aluminium
on the small end bearings causing them to
fail and take the conrod with them ), plus
a new "3G3" piston to suit the new
cylinder.
- The inclusion of 38mm "Powerjet"
Mikuni carburettors to further enhance the
new engine's usability through the ability
to fine-tune the midrange mixture more effectively
and also reduce the risk of seizure at high
rpm, while actually contributing to the increase
in peak output at the same time.
- A new, revised, lighter weight frame, which
had a bad tendency to fail around the headstock,
which is why so many of them were re-inforced
in this area, or had aftermarket frames replacing
the Yamaha items. (Click here to read about
aftermarket TZ frames.)
- A new box-section aluminium swingarm, aluminium
body rear shock (still with adjustable preload
and rebound damping only).
- New forks featuring 3-way adjustable spring
preload via. an external adjuster on top of
each fork tube, as well as revised fork internals
designed to reduce the front end "patter"
being experienced by a number of 350 riders.
- A new fairing which dispensed with the
separate belly pan and was a sharper shape
at the bottom-front (behind the front wheel).
The fuel tank was now a tapered shape to match
the sloping upper frame rails and the seat
unit was changed to a more "current"
shape.
- Minor changes included: the cylinder drain
pipe, inner main bearing circlip/washer, gudgeon
pins, introduction of an oil level "dipstick"
and new ignition pulser coils, exhaust mounts,
clutch cover and an additional o-ring was
included in the exhaust header to assist sealing.
Frame failures around the headstock area were
a common problem with the "F" model
350's, for this reason a large number of owners
chose to ditch the stock frames and replace
them with units made by such manufacturers as
Nikko Bakker, Bimota, Spondon, Maxton, etc.
Others chose to reinforce the stocker with additional
bracing such as that shown in the photo.
 1980's
TZ350 G was virtually the same as the previous
"F" apart from another attempt at
improving the conrod, reverting back to the
older "E" inner main bearing circlip/washers,
a revised piston silicon content as well as
strengthening in the sides of the piston, and
a different "dipstick". Another change
was the way the ignition rotor was bolted on
to the crankshaft. The timing side crank wheel
had an external thread and nut, where the earlier
models had the standard 7mm internal thread.
The 350 "G" was never really improved
on, despite Yamaha releasing another model,
the "H", which was really just a case
of the factory using up a lot of it's stock
of parts, giving up further production of the
mighty TZ350 once the FIM dropped the 350cc
World Championship class in 1982.
Information kindly provided by www.tz350.com
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