6 THINGS YOU NEED TO KNOW…

Motorcycle News (UK) - - GARAGE -

Less is more

En­gines don’t get more pow­er­ful by magic. It comes from re­duc­ing in­ef­fi­cien­cies: mak­ing valves lighter, cut­ting ro­tat­ing mass, re­duc­ing fric­tion, and so on. We worked on mak­ing mov­ing parts lighter – for ex­am­ple, using spe­cial steel for the ex­haust valve rocker, and chang­ing roller bear­ings in the con­rod for plain ones.

Fewer vibes

The lower bal­anc­ing shaft works against the os­cil­lat­ing masses of the crank­shaft and big end. But that also cre­ates mo­men­tum, and so a force. The up­per bal­ancer works against this force. There was a lot of brain work on this be­cause of the lever­age: if the bal­ancer is a big­ger dis­tance from the crank­shaft, its weight is less; shorter dis­tance, more weight. And it must ro­tate at the same speed as the crank­shaft. We mounted ac­cel­er­a­tion sen­sors in the en­gine and found vi­bra­tion was re­duced by half.

Trick breather

Breath­ing is im­por­tant to cut the pump­ing losses. But you must also re­move the oil mist from the air in­side the en­gine. We used the up­per bal­ancer weight to solve this prob­lem. The en­gine breathes through a hole in the bal­ancer, but be­cause the bal­ancer ro­tates at crank­shaft speed the oil droplets in the air are flung away by cen­trifu­gal force.

Higher revs

The pis­ton is 105mm, 3mm wider than be­fore, and the stroke is 80mm, 4.5mm less for higher rpm and a greater pis­ton area. The pis­ton is milled to re­duce weight. The DLC pis­ton pin coat­ing saves the weight and vol­ume of a roller small end. It’s hard con­trol emis­sons with a very flat com­bus­tion cham­ber, so we use twin plugs.

Charge res­onator

This is a closed cham­ber con­nected to one in­let port. The res­o­nance it cre­ates helps on part-throt­tle by mod­i­fy­ing the in­let pulses. It also al­lows us to run dif­fer­ent ig­ni­tion tim­ing on the two plugs, be­cause the sec­ond plug’s spark is in the ‘shadow’ of the first. It was not nec­es­sary to reg­u­late the vol­ume of the cham­ber, but to place it at the right an­gle to the in­let tract.

Cam ten­sioner

When you start the en­gine there is a lit­tle rat­tle at first. That’s be­cause we use a hy­draulic sys­tem for the cam drive, and for the first two sec­onds there is no oil pres­sure. On a me­chan­i­cal ten­sioner, there is no ‘give’, so there is a lot of force on the tim­ing chain but this way, there is less stress. Ac­cu­racy at high rpm is not a prob­lem be­cause with the plain bear­ings we are work­ing with very high oil pres­sure.

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