Q: FIRST AND FOREMOST, IS THE 2016 YZ450F
BETTER THAN THE 2015 YZ450F?
A: Yes, but the changes are small qualitative steps as
opposed to a major overhaul of the existing 2015 YZ450F.
Q: WHAT CHANGES DID YAMAHA MAKE TO
THE YZ450F ENGINE?
A: Don’t forget that the YZ450F was brand new for
the 2014 model year. Under the current pattern of four-year
development cycles, any changes to the bike this year are
icing on the cake, because a new bike isn’t in the cards
until after 2017. That said, Yamaha did try to address some
engine issues that MXA was critical of. All of these parts
can be retrofit on a 2014–’ 15 YZ450F. Here is the list:
(1) Cams. The exhaust cam has 0.3mm more lift. Valve
lift is the distance that the valve is lifted off of its seat.
Increasing valve lift, without increasing duration, can yield
more power without much change to the nature of the
power curve. On the 2016 Yamaha YZ450F, the exhaust
cam opens the valves later, closes them sooner and has a
duration of 8 degrees less. Most important, the overlap was
decreased from 80 degrees to 68 degrees (at high engine
speeds, overlap allows the rush of exhaust gases out the
exhaust valve to help pull the fresh air/fuel mixture into
the cylinder through the intake valve). The intake cam has
0.1mm less lift, which for all intents and purposes is negligible. What does all that mumbo-jumbo mean? There is more
low-end power and a better transition into the middle.
( 2) Valve springs. The 2016 valve springs are slightly
stiffer than the 2015 springs. More important, the spring
design has been changed to eliminate coil bind at high rpm.
( 3) Gear stop lever. In 2014, there were some failures
of the ball bearing-equipped roller on the gear stop lever, so
in 2015, the ball bearings were replaced with a plain roller,
which would not explode like the ball bearings had. For
2016, the gear stop lever not only gets a 20-percent-stiffer
spring, but the plain roller is now supported on both sides
of the stopper arm.
( 4) Dog shape. Yamaha has changed the dog shape on
the gears to allow for more precise shifting, especially on
the previous weak link while up-shifting. Additionally, the
gap for neutral has been reduced to lessen the chance of
accidentally popping the bike out of gear while racing.
( 5) Clutch pressure plate. A new machining process on
the clutch surface of the YZ450F pressure plate ensures a
smoother and flatter gripping point for the clutch. The 2015
pressure plate was rougher at the micron level.
( 6) Impeller. Yamaha has installed a new impeller in
the water pump; however, the impeller’s shape, vanes and
dimensions remain unchanged. Instead, Yamaha drilled holes
in the backing plate of the impeller to relieve pressure on
the seal side. This equalizes pressure on both sides of the
pump and improves water pump seal life.