TZ Cylinders

In 1973 Yamaha introduced the TZ series. From 1973 to 80 the TZ250 & 350 used a piston 
port parallel twin monoblock design based on DS7/R5 cases. The TZ250G being the fastest of 
the monoblock 250s with an intake so big they had to extend the intake port roof down 4mm in 
the middle for piston/ring support. Piston life was short but it sure made power. Fastest of the 
TZ350s were the F&G with their 6 transfer port cylinders.

Early TZ250

TZ250G

Early TZ350

TZ350 6 transfer

In 1981Yamaha totaly redesigned the TZ250 engine. Having reached the limit of intake port size 
in the G, the H models crankshaft rotation was run backwards to put piston thrust on the cylinder 
wall opposite the intake allowing further increases in intake port size. Also new was Yamaha's 
exhaust power valve system which in it's infancy was having teething problems. Two stroke tuner 
Hans Hummel provided a solution by producing his own non power valve cylinders.

Hans Hummel TZ250

In 1985 Yamaha again Redesigned the TZ250 engine. 1985-1987. Switching for the first time to 
case reed induction allowing for much needed transfer area (2 new boost ports were the intake 
once was) creating needed bottom end & thereby also a wider powerband.

1987 Tz250

In 1988 through 90 Yamaha reversed the cylinders & tilted them forward to 60deg putting the 
carbs in front & the pipes coming straight out the back under the seat.

In 1991 Yamaha went to the V-twin design allowing room for good transfer design while letting 
the crankshaft & engine to become narrower.

91 TZ250          V-Twin             92TZ250

                                                                        TZ750                                                              OW31