RD-500 (Devils in throttle )

TheYamaha RD500LCis a high-performance,two-strokesportsmotorcycle, also known as theRZ500in Canada and Australia. A lightened but detuned version known as the RZV500R was developed for the Japanese home market. Styrict United States Environmental Protection Agencyregulations meant that the RZ500 was notavailable for sale in that country. Produced for a short period between 1984and 1986 it has become a sought after collector’s machine.DevelopmentWith the success in the early 1980s ofKenny Robertsand theYamaha YZR500inGrand Prix motorcycle racingYamaha realised that a road going replica of their 500 cc racing machine would sell well. Using the similar technology of the smaller RD series of two-stroke motorcycles the RD500LC was launched ​

in1984.DesignEngineYamaha YZR500.The RD500LC (Race Developed 500CC Liquid Cooled motorcycle)uses a 50-degree, twin-crankshaftV4 enginelayout. Linked YamahaYPVSexhaust power valves are controlled by a single electronic unit andservo motorand are designed to give a broaderpower band. The engine also features intakereed valvesunlike the YZR500 racer which used rotary disc valve induction. The reed valves use two different intake arrangements, the lowercylindersare fed throughcrankcasemounted reeds; the upper pair use cylinder barrel mounted reeds. The fourMikunicarburettorsare side mounted in pairs and feed each cylinder through 90 degree intakemanifold. The lowerexpansion chambersexit normally but the upper pipes cross over each other just behind the exhaust ports to maintain the correct tuned length.The dual crankshafts are geared directly to theclutch, while the front crankshaft also drives acounter balancer shaftmounted between the two crankshafts. The counterbalance shaft, unusual on a two-stroke, assists with dampening engine vibrations. The engine is cooled bythermostaticallycontrolledliquid cooling, an auxiliary electricfanmounted behind theradiatorcuts in at quite high but acceptable working temperatures (e.g. when stationary in traffic).Lubricationis by direct injection in to the inlet manifoldsusing Yamaha’s ‘Autolube’ pump system. Normally controlled in other two-stroke engines bythrottleposition, the engine oilpump is controlled by the YPVS servo motor ensuring that the oil supply is not shut off at high enginerevolutions.TransmissionRD500LC rear viewThe RD500LC uses a six-speed sequentialclose ratio gearboxwith the usual road-going ‘one down and five up’ sequence, the gear shafts are removable from the right side of the engine without the need to split the crankcases. The clutch is of the wet, multiple-disc coil spring type and is cable operated. Unusually for a two-stroke engine the gears and outer crankshaft bearings are lubricated by a separate crankshaft driventroichoidoil pump. Final drive is by conventional for the timeO-ring chainandsprockets.ChassisTheframeof the RD500LC is manufactured frommild steelbox-sectionand uses a perimeter layout. The rearshock absorberis unusually placed horizontally under the engine and uses the lower crankcase as a mounting point. The under-seat area is occupied by the upper cylinder exhaust chambers, the oil pump and one-way valves, the battery andthe YPVS (Yamaha Power Valve System) servo motor. The battery is of the ‘wet’ lead acid type and a cut-out is provided in the right side panel to view the acid levels without having to dismantle half the bike! The rear of the shock absorber connects to anextrudedaluminium alloys winging armvia several forged aluminium rocker arms. An unusually smalldiameter16-inchwheel is held between 37 mm (1.5 in) spring and oil dampedforkswhich featured adjustable anti-dive units.The RD500LC uses twin ventilateddisc brakesfor the front wheel with a single ventilated disc at the rear. A solo seat cowl was originally provided to cover thepillionseat when not in use.

The Japanese market RZV500R differs from the RD500 bynothaving a rear-mounted pillion grab handle fitted (which gives a cleaner, more race-oriented look to the motorcycle).Electrical systemRD500LC Speedometer and TachometerThe RD500LC features a standard 12-voltelectrical system. Yamaha’s self-cancelling indicator unit is used and avariable resistancegauging systemis used to monitortwo-stroke oiltank contents with associated warning lights.Nippondensocapacitor discharge ignition(CDI) is used in conjunction with twocoils.RZV500RThe RZV500R was designed exclusively for the Japanese home market although many have been exported privately. The RZV500R features upgraded parts not found on the standard RD500LC and RZ500. A major difference is the hand-welded aluminium frame, which is significantly lighter than the steel version used on standard models. The water temperature gauge also doubles as a fuel tank contents gauge at the push of a RHS lever (very useful feature given their fuel consumption) and the front-fork preload can be altered from the top of the forks. There is also a red light mounted within the tachometer housing that comes on at the equivalent of 55 mph (Japanese maximum national speed limit). The speedo is of course calibrated in KPH.The front forks are air assisted with rebound damping adjustment. The rear brake and gear levers are cast from aluminium, as are the clip-on type handle bars. These chassis modifications added up to a weight saving of 20 lb (9.1 kg). Theengine was detuned to 64 hp (48 kW) to comply with Japanese legislation. This was achieved by restricting the internal diameter of the exhaust pipes and changes to the carburettor jetting.These restrictions are easily changed to the RD500 specification by opening up therestrictor plates in the exhaust to create the same diameter hole as the exhaust pipes had as standard and the re-jetting of the carburetors to suit.


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