CLASSICRACERINDETAIL
46 ClassicRacer
M
oto Guzzi builtatotal of
sixcomplete500cc V8
motorcycles, and while these
differed slightly in design, they
all had the sameincredibly compactdry-sump
water-cooled engine architecture, measuring
44 x41mmforacapacityof498.73cc
(interestingly, Honda adopted thesame
dimensions forits 250 four the following
decade).
Thetwo banks of cylinders were set
at a90º includedangleon aone-piece
cast magnesiumcrankcase, whichalso
incorporatedthe unit-constructiongearbox
withgear primarydrive. Andinafar-sighted
move copied by Ducati30 years laterin
producing its first 851ccV-twin Superbike
engine, the crankcase casting also featured
aribbed 40mmdiameter bronze-bushed
pivot to housethe rearswingarm to increase
stiffnessand save weight.
Theresultant engine weighed just 56kg,
including the eightcarburettorsand floatchambers,andinmeasuring amere460mm
across, allowedthe complete bike,fitted with
fullstreamlining,tobeonly30mmwiderthan
Guzzi’sworld champion350 single. Carcano
had calculatedthat the FIM’sstipulationof a
minimumof 40º of steeringlocknecessitated
adustbin fairingbeingatleast 460mm wide,
hence theviabilityofseeking to packeight
cylindersinto thisspace rather than just one,
twoorfour.And in doing so, he created a
bikeweighinganamazing137kgdry with full
streamlining(134kgwith partialstreamlining),
just 5kgheavier than asimilarly faired Manx
Norton single.
Theoriginal 1955 V8 engine’sforged
one-piecefive-bearing 180º flat-plane
crankshaft with full-circle flywheels
necessitated bolted-upsteel conrods with
split roller bearing cages. It waschosenby
Carcano to deliveralower, morecompact
crankcaseformat,and wasproducedby
Hoeckle in Germany to Guzzi’sdesign.To
buildthe engine,thiscrankassembly wasAskany race fantonominatethe mostexotic and mostdesirableGrandPrix racereverbuilt, and the MotoGuzzi 500
V8 will be almostcertainly beTheOne. It only racedfortwo years in 1956-57and neverwon aWorld Championship
GP.Despitethat, there’s an aura aboutthis motorcycle that’sentirelyin keepingwith its improbablespecification.insertedthroughthe opensidesofthe
thin wall crankcase–both this casting and
the outercovers were just 4mmthick, an
amazing technical achievementforthe day
–then bolted to internal webs housing the
threecentral rollermain bearings,again with
split cages.The outermainbearingswere
mounted in the crankcase covers,with a
ball bearingonthe driveside and atiming
side roller.Once in place, the cast three-ring
Mondial pistons withdeepvalveinsertsand
asurprisingly high degree of squish forthe
period, were fitted to the plain-bearing
small-ends, originallydelivering 10:1
compression, later raisedto 11.4:1 for1957.In
this form,the first V8 enginedelivered 62bhp
at 11,500rpm–afigurethat eventually roseto
79bhpat12,500rpm midway through1957in
the engine’s finalform,with maximumtorque
of 47.6Nmdelivered at 9300rpm,and the
engine tested to 16,000rpm without bursting.
But owing to concerns aboutcrankshaft
stiffness,and the high-frequency secondary
vibration endemicin aflat-plane crankthat
had ledtosuccessive retirements in the V8’s
debutseason, for1956this wasreplaced
by a90º crossplane crank,originally also a
one-piece Hoeckle component, whichinturn
dictated ataller,more spaciouscrankcase
casting.This didn’t cure the vibration, so for
1957 another 90º crossplane crank wasalso
sourcedfromGermany, this timeanine-piece
built-up onefromMunich-basedAlbertHirth,
whichwas already workingwith Guzzi’s
neighbouring rival Gilerain producingthe
crankshaftfor its world title-winningin-line
four.Hirth had furthermore alsobuilt the
cranksusedonthe dominantNSU Rennmax
250twins that hadcompletely outpaced46 ClassicRacer
g g044 MotoGuzzi500 V8_SEP.indd 46 26/07/201715:23:10