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  The works motors for 1973 used an all new crankcase design made from sand cast magnesium and featured a new style clutch actuating arm that went through the top of the cases.  This gave a much more positive clutch feel.  Prior to this they used the DT style actuator that had a worm gear attached to a small case.  This system resulted in too much flex and the clutch action suffered.  All the gears are hand machined and drilled out as is the clutch basket.  Even the primary gear attached to the crankshaft is machined and drilled for less weight.  Titanium is used inside the motor where ever possible.  The cylinder is a special works model with a porting arrangement designed more for torque.  The cylinder was then modified by Hakan's long time mechanic Eije for even more torque.  Eije modified the shape of the rear transfer port to distribute the fuel mix more evenly.  This was done by cutting the cylinder fins and accessing the port from outside the cylinder.  Once the modification was finished, a plug was then welded in place.  The result was a much broader power band. This modification was done very late in the year, possibly after the GP season ended.  Magnesium cylinders were tested but discarded because they didn't dissipate the heat well.  There was also at least a half a dozen different reed cage and intake manifold set ups available that altered the torque curve.  A 36mm mikuni was used exclusively.  Magnesium carburetors were tested but there was a problem with the aluminum slide sticking when the motor got hot.  Notice the shift lever, it is cut and re-welded near the end for the perfect length for Hakan.   Every single fastener is either titanium or aluminum.  The motor is very light.



  There were several different ignitions available, each offered a different torque curve.  Hakan settled on the one for more bottom end power.  With the new shock location a new pipe design was used that starts on the left, crosses over the top of the motor and exits on the right.  This was done to maintain the proper tuning length.  It was made in two parts so it could be easily removed.  Different pipes were used depending on the track.  The pipes themselves are a work of art.  They are hydro-formed out of very thin gauge steel. No silencer was used and the bike is very loud.  Yamaha went all out to save weight on this bike, even the fitting on the end of the spring where the pipe attaches to the cylinder is titanium! 




   The monoshock location restricted space for the air box, so a duel filter system was incorporated to maintain the proper air volume.  The air box itself is made of very thin layered fiber glass, as are the air filter covers.  The entire assembly weighs just ounces.  Also because of the monoshock location, the black box and ignition coil that were previously mounted under the tank, were relocated as you can see in the photo below.  The black box was placed in such an unconventional location for the time, that an American magazine actually published a photo of it claiming that it was a lead weight ballast!  1973 was the first year that the works Yamahas used the Timken style bearings at the steering head.  This provided a much more positive front end.  The top triple clamp is sand cast magnesium while the bottom is billet aluminum, and all the related  fasteners are titanium.  This was also the first year for Yamaha to knurl their fork legs where they make contact with the triple clamps.  As you can see, the chassis was a large part of Yamaha's focus for 1973.



   Hakan's bike displays a certain mystique that was unique to the early Japanese works bikes.  They were very cobby and very functional looking.  It was this combination that had the fans going to the races to see the bikes as well as the race itself.  They were constantly changing from week to week as motocross bikes were now entering a hyper-evolution phase in design.  More often than not, it was the bikes themselves that stole the show.

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