(Jacob Rumans) #1

Allen MMillyardd
Award-winning mootorcycleengineer!

Using G-clamps to partially engage web on to main journal.

Trial fitofpart-built crankshaft into upper crankcase.

Pressing on web after setting position
on milling machine.

Set up on milling machine to align crank-pin five with crank-
pin two.

Onceall partswere strippedIcleaned
off th etarnish and hardened oil stains
with afine wire brushand brak ecleaner,
theninspected all the parts for wear or
damage. TheZ1crankshaft has
substantial,purpo se-made roller bearings,
and overyears of use they have proved to
be extremely reliableandrarelyneed
attention. My two donor crankshafts had
no signsofc ondensation damage or wear
and theroller bearing tracks stillhad the
original cross hatched lapping marks on
the bearing surfaces, indicatingagentle
lifewithgoodoil. Looking at all theparts,
Icould seethatthe central four setsof
websand outer leftpair could be made
with unmodified original parts,but the
websfor the right-handside wouldneed
somemodificationto maintain alignment
with main bearing journalsand balance
as asix-cylinderengine, whichIwill
explainlater on.
Ihad decidedto configuremynew
crankshaftsot hatthe pistons will rise and
fallinp airs at 120-degree intervals, giving
a1-4-2-6-3-5 firing orderfor smooth
running. The first thingIdid was to

mountthecentral part of thecrankshaft
with the centralconnectingrods three and
four on to my lathe ina3-jawchuck. Then
Iset connecting rod fourontoapin held
in the tool post to prevent thecrankshaft
from rotatingwiththe bi gend at the six
o’clock position .Ithen setupt he degree
disk andset apointertozero. Ithen
carefully traversed thesaddle backto
disengaging the location pin from
connecting rod four and engaging it with
connecting rod five, which wouldlocate
the web in the correctrotational
orientation on the mainjournal with slight
pressurefrom thelathe tailstock
temporarily holdingitinplace.
The central portion of crankshaft was
then rotated 120 degrees, while the new
web was held stillby connecti ng rod five
that was attached to the pinlocated inthe
tool post. Alighttap with ahammer
engaged theweb sufficiently on to the
main shaft so thatIcould transfer the
part-built crankshaft to my press to press
the new web fully home.Ireturned the
my lathe and

re-checked thatrotational alignment
between crank-pin four and five was still at
120 degr ees and nothing had slipped.
The next job was to align crank-pin five
with crank-pin two, which had to be
aligned togethersot hatpistons twoand
five wouldrise and fall togetherat120
degrees to pistons three and four.
To do thisIused aset of slip gauges
and my flatcastiron milling machine table
to se tupthe crankshaft with two of its
main bearings resting on identical size slip
gaugessot hatthe webs were freeto
rotate, then clamped crank-pin five on to a
two-inchslip gauge and lightly clamped it
in place.Ithenappliedlight pressureto
the crankshaft to hold it inplace while I
set upcrank-pin two by resting it on an
identical two-inchslipgauge and lightly
clamping it inplace. With crank-pin two
held in thecorrect alignment with
crank-pin five,Iused acouple of G-clamps
to carefully engagethe webon to th emain
shaft sufficiently tohold it inplace while I
transferred the crankshafttomypress.
Once pressed together,Ireturned the
crankshaft to the milling machine and
re-checked withthe slip gauges as
detailed above to ensurecrank-pins two
and fivewere aligned perfectly before
movingon to the next stage.cmm

54 /classicmotorcyclemechanics
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