32 ClassicRacer
CLASSICRACERMACHINES
To p:HaroldWillisandClaraattheTTweigh-inRight:TheRestorationTe am!Lefttoright,SamRhodes,Grahame
Rhodes,GeoffBerry,JohnKidson,IvanRhodesonbike, HaroldBeal,
RobWiggins,JohnGoodall(thelate)BrianJames,BobHiggsand
DavidTo ng.Pete Welchhelpedwithspecialistmachiningbutcould
notmakethephoto-shoot.RODNEYWILDSMITH.Messrs Irvingand Willis foundavane-type Foxwell unit, which
wasneverintended foruse withinternal combustionengines(see
page34). Factory records showthat engineKTT 240 wasbooked
out to Willis.Theexperimental set-up employedasimple biscuittin
as aplenumchamber,but whenthe enginewastried on the test-
bedthe output measured 30hp, comparedtothe 22 of anormally
aspiratedengine. It wasaremarkableresult, although it should
be notedthat the enginewasgettingthe full benefitofthe more
intense inlet charge, as the supercharger wasbeing driven by an
external powersource.
With suchapositiveresult, andasthe bottom end assembly
appearedtobeadequate,the decision wasmade to continuethe
experimentwith acomplete motorcycle. Using the sameengine
as thebasis, the drawingoffice cameup with variousnecessary
modifications. Feedingthe carburettor with pressurised air means
the entirefuel system,fromthe carburettor anduptoand including
the fuel tank, also has to be pressurisedtofunction. Aspecial
framewas created, althoughitused various lugs fromthe factory
parts bins.Heavy fuel consumptionwas anticipated, so aspecial
fuel tank offered increasedcapacity.Whenitwas fitteditlooked
the ‘Pistol Grip’style adopted by NewImperial.Aswellas
forengineering, Willis wasalsoanexcellentrider,posting
lace finishes in boththe 1927 and 1928 JuniorTT races.
hismostmemorablelegacyishis largelexiconofwords
motorcyclesand theirconstituent parts.Thus Willis referred
eunusually-shapedfueltank as a‘cow’sudder’. Following
e, whenthe pressurisedfuel systemhad to vent,itdid so
whiffling’sound, hencethe ‘Whiffling Clara’ sobriquet.
sengineused the standard cast iron cylinder headwithcoil
ings. Behind the engine,onthe rightsideofthe gearbox,
Official Receiver’, Willis’s appellation forthe largetank that
plenumchamberfor the pressurisedfuel/air mix.
xwell blowerwas mountedlowdowninfront of the
and wasdrivenbychain fromthe crankshaft. With the
al Receiver’behind,the wholesystemrequired alot of
ing.Initially,the bikewas fittedwith Willis’s four-speed
ox unit with rack andpinion selector,but this waschanged
four-speed constant-mesh version. Apparently,hard
ng could result in the iron cylinder headglowingwith the
at. Anew designwith hairpin valvesprings cast from
uminiumbronze(‘doorknobmetal’accordingtoWillis)
ided heat dissipation andthe sameheadwas eventually
usedonproductionKTT Mk.IVmodels.Thesupercharger
arrangementwas soon changed,with the carburettor
workingat atmospheric pressure and the, now
down-stream, blowercompressing thefuel/air mixture.
Unevenfuelling remainedaproblem. Underriding
conditionsthe plenumchamberfilled with afuel-rich
mixture on the over-run, chokingthe engine when the
throttle wasopened again.This wasaddressed witha
special pressure relief valve, apparently an itemdeveloped
by Amal forthe Air Ministry. This wasconnectedtoavalve
ifter-type leverthathad to be operatedmanuallybythe
ider,clearingthe surplusgas and allowing the engine to
un cleanly.
AftersomeencourAftersomeencouraaging test results hopeswerehighgingtestresults,hopeswerehighfueltank
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