Practical Sportsbikes (UK) - - Reader Restoration -

In the mael­strom of me­chan­i­cal mar­vels the man­u­fac­tur­ers came out with in the 1980s, it would be easy to for­get the sig­nif­i­cance ofyamaha’s 1985 FZ750. It wasn’t just the tech in the en­gine.the mo­tor’s de­sign also set a new bench­mark for pack­ag­ing.

Yamaha cre­ated the first four-valve com­bus­tion cham­ber in a mass-pro­duced bike with the al­most-for­got­tentx500 twin.the FZ750 went one bet­ter with five; three in­let and two ex­haust. It would be­come ayamaha hall­mark un­til a four-valve lay­out was adopted for the 2007YZF-R1 to meet emis­sions regs.the key claim for the five-valve de­sign was that through hav­ing 10 per cent more in­let area than a four-valve com­bus­tion cham­ber, torque and power were in­creased through bet­ter cylin­der fill­ing. Be­ing smaller and lighter the valves al­lowed the en­gine to rev higher too.an­other ben­e­fit was that valve springs could be lighter for fewer me­chan­i­cal losses and the seats got an eas­ier time too. Dished pis­tons al­lowed for an el­lip­ti­cal com­bus­tion cham­ber that gave more space around the spark plug than a four-valve pent roof com­bus­tion cham­ber.

The cylin­der head was a clever two-part de­sign.the top cam case is re­moved for valve shim changes while a lower case con­tains the com­bus­tion cham­bers and valves.

How­ever it was the down­draught in­take sys­tem, learned fromyamaha’s F1 en­gine ex­pe­ri­ences that was key.the carbs are mounted hor­i­zon­tally and the fuel/air mix­ture goes straight down to the com­bus­tion cham­bers – a real revo­lu­tion.to ac­com­mo­date this the block had to be an­gled for­ward. In do­ing soyamaha pushed the pack­ag­ing bound­aries.true mass cen­tral­i­sa­tion was born.

“Yamaha pushed the pack­ag­ing bound­aries. True mass cen­tral­i­sa­tion was born”

One hell of an en­gine, rest of it not bad ei­ther

Five valves per cylin­der, and Yamaha ex­per­i­mented with seven – and even nine

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