Classic Dirt Bike — Autumn 2017

F

or an enginedesignedin the 1930sto

still be the choiceof aracer determined

to win in the then ‘modern’era of 1968,

the basicconceptof that enginemusthave been

prettygood.At that time,TheMotorCycle’s

man VicWilloughbyvisitedmulti-timeBritish

grasstrackchampionand talentedengineerDon

Goddentofind out whatthe lad did to make

thoseengineswork waybeyond the maker’s

wildestexpectations.

Immediatelyhe foundtherewereremarkably

fewchangesfromits inceptionto the latest

1960smodel.The crankcaseswerecast in the

magnesiumalloyknown by its tradenameof

Elektron,the con rod waseitherinDuralumin–

anothertradename–orsteel.Willoughby went

as farastosay the drawingusedin the feature

wasanupdatedone fromthe 1930sand all the

artisthad to do wastoerase thetrack carburettor

and replaceit with aConcentriccarburettor,

shortenthe cylinderand con rod alittle and

eraseapushrodreturnspring.The featurewent

on to say the speedway JAPhad the rightsort of

power to propelaspeedway bikeand rideroff

the line in the best time possible.Thatthis power

wasflaggingat alittle morethan 5000rpm,and

all butgone at 6000rpm,wasoflittle matterto

arace on atrack of 440 yards.The JAPmotor

was, whilenot the only one in use, dominating

the speedway scene.

Whenthe race trackwas1000 metreslong,

however, it wasadifferent kettle offish and

with the standardJAPmotor Goddenbarely

had enoughpower to qualifywhenhe made

his earlyforaysinto the scenein Germany.

Clearlysomethinghad to be doneand he set

aboutit with agood measureof commonsense,

engineeringtalentand adeal of determination.

He did it to suchgoodeffect that threeyears

later he waschallengingfor the top spot in

the longerformat.This,thoughtWilloughby,

wasastory worth hearingand detailingin the

paper.With agrass trackcareergoingbackas

faras1953 Goddenhad earnedhimselfnine

Britishchampionshipsusingequipmenthe’d

built himself,and latterlyby co-operating

with Alf Hagonto provide acommercialJAP

tuningservice.This wasthe basisof the motor

Willoughbywentalongto hear about.In 1968

the basicJAPspeedway motorwasavailablefor

would provide a‘GoldTop’ engine,likely a

referenceto the gold top milkwhichwasextra

creamyand had foil in gold ratherthan silver;

the ‘GoldTop’ JAPwas reckonedto be the

creamof the crop.To distinguishtheirhigh-

performanceenginefromthe rest, Goddenand

Hagonhad the rocker covers anodisedyellow–

it’sjust ashamethe effect can’tbeseen in black

and whitephotos.

Starting with thestandardJAPmotor,Godden

first addressedthe cam timingwhichwentfrom

the inlet openingat 45 degreesbeforeTDC,and

closingat 62 degreesafterBDC–the exhaust

openingat 65 degreesbeforeBDC,and closing t

Do

Godden

Topgrass andlong track racer

Don Goddenwas interviewedfor

The MotorCyclein 1968to see just

how he managed to makea35-year-

old enginedesignworkso well...

thebasicJAPspeedwaymotorwasavailablefor

£140,howeverfor another£30 Godden/Hagon

BELOW:Whenfettledtohisexactingstandards,Don’sJAPswerea

matchfortheforeigncompetitiononthelongtracksofEurope.

TOPMIDDLE:Evenvalveguidescanbeusefully

modifiedtoincreasereliabilityandpower.

TOPRIGHT:Camfollowersgetthepolishingand

relievingtreatment,too.It’sall aboutstressrelease.

DDoo

odden

oon

dd

o

To

D

Th

Top’engine.

D

ABOVE:Asmalltestof

observationhere–spot

theworncrankpin...

TOPLEFT:Magneto

timingandoperationis

modifiedinaGodden‘Gold

T ’ i

This four-pagespecialfeatureisalsoinour new publicationBroadslide.

042-049mbzBroadslide_044.indd 40 02/08/201712:39:06