Difference between revisions of "Yamaha TZ350"

1973 saw the introduction of the bike which was about to transform the 350cc GP class worldwide, the incredible [[Yamaha]] '''TZ350A'''. The inclusion of [[water-cooling]] in addition to other slight improvements over the bike's [[air cooled]] predecessors, the [[Yamaha TR2|TR2]], TR2B and [[Yamaha TR3|TR3]], saw Yamaha's 350cc production offering fast becoming an almost unbeatable weapon in the hands of the right rider.  This boosted horsepower from ~55 to 65 [[horsepower]], but most importantly it could sustain that power throughout the whole race.  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.   

[[Image:Yamaha-TZ350E-Macau-Museum.jpg|left|thumb|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.]]

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.)  

#    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.

#    A new box-section aluminium swingarm, aluminium body rear shock (still with adjustable preload and compression damping only)

#    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.