17
Robertinactiononhiswayto
worldchampionshipsuccess
atthe 1964 BritishGP.Youneed
Themachineusedtowinaworldchampionship
alwaysexcitesinterest...mustbesomething
specialafterall,mustn’t it?Words:Tim BrittonPics:Mortons Archive,Nick NichollscollectionT
he Sixties hadn’tquite gotto
the Summerof Love or even
started swingingwhen20-year-old
BelgianJoel Robertmade hisfirs t
of manyindeliblemarks in the history of
motocross.In August 1964 MotorCyclinggot
hold of afeatureabouthis championship-
winning machine, determinedto unearth
afew secretsthesefactoryteamskeep
to themselves.
The presswere to be disappointed, as
theyfoundout the machinewasexpertly
maintainedand if not built regardlessof
cost –this wasthe Easternbloc after all.
The teambikes were in tip-topcondition
and prettystandardfare as well as being
basicallywhat aracer could buy but with the
aforementionedrace-shop attention to detail,
though that could alsobeachieved in a
privateenvironment.
It seems CZ had reliedon simplicity rather
than revolutionary conceptstoproducetheir
winningmachines. The bikeinthis featureis
Robert’smachineand shows the robustness
of the enginewhichhad beenaCZthing
for sometime and wouldaid restorers
in the then future as these engines are
virtually indestructible.
Relyingon yearsofgoodengineering
practice,coupledwith the experiences gained
in competition, CZ produced amotorcycle
whichwaspowerful,flexibleand strong
enoughto outlastthe rigoursofaGPseason.
MotorCyclinglearned the enginewas a
simpletwo-strokeinunit constructionwith a
four-speedgearboxand the resultant unit has
apeak power outputof26bhpat 5900rpm.
Surelytheremustbesometrickeryinside
the enginemasqueradingas standard? No,
sorry, and Iquote:“...theengine employs
aclassicloop-scavenge system...”which
basicallymeansthe freshcombustion charge
is drawn into the crankcaseas the piston
risesand ispushedthrough transferports
openedand closedby the pistonas it travels
up and downthe bore creatingpressureat either end of the scale.Thesetransfer
portsare formedinboth the barreland
the crankcases.
In amovetoprovide enginerigidityand
pistonsupport, the barrel has an extended
skirtorspigotextending deepinto the
crankcasemouth.Aha, the barrel and cases
must be magnesiumorother unobtainium
mustn’tthey? No, it is cast iron for the barrel
and aluminium alloyfor the casesand head,
so hardlyfancy. The headdoes have atwin
plug arrangement and asquish bandto
promoteathoroughmix of the combustion
chargeso the plugscan igniteit and produce
theright amountof power from the mixture
squeezedat 10.5:1compression ratio.
The backbone of an engineis the
crankshaft and CZ had madean extremely
rigid unit with smalldiameterflywheelsfor
snap accelerationas well as makingthe
crankcase pumping muchmoreefficient.To
keep the crank turning easily,CZused a
doublerow bearingonthe ignitionside with
twoball bearingsonthe drive side.
They also moved the clutchto the
crankshaft whichmeansit operates under
muchless torquethan if it wasonthe
gearboxmainshaft. Adownsideis this
arrangementgives thegearboxitselfa
hardertime becausethere’sless chance
of the clutch slipping.CZrealisedthis, so
did alot of redesignworkinthe cluster.
Becausethere had beenissueswith earlier
modelsthis redesignof the clusterincluded
such thingsas using needleroller bearings
rather than bronzebushes.Why? Because
needlerollersdon’t needalubrication hole
inthe shaft, so instantly aweak pointis
eliminated. This robust250 unitdidn’thave
achain as primarydrive, usinginsteadspur
gearsdeemedtoo noisyfor aroad bikebut
acceptableon arace machine.
SomethingMotorCyclingfoundinteresting
wasthe gear selectionmethod,or rather
it and it’saccess.Acceptinginthe heat of
the momentascrambleris more concernedJoel Robert’s CZ
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