big end cage. In the event of damage to the crankpin, by reason of deto-
nation, due to excess ignition advance, pre-ignition (soft plug), or
unsuitable fuel, it is essential to replace the roller cage as well as other
big end parts. The crankpin and liner for con rod have a mirror like finish
(5 micros) and are made to close limits. To ensure uniformity each roller
should be measured by micrometer and selected to a uniform diameter;
1962 big end assembly uses 28 ¼" x ¼" rollers.
Timing side shaft. Normally the thread for the small timing pinion is
left hand. A number of engines were issued with right-hand threads, these
shafts can be identified by the use of a tab, or lock washer, between the
pinion and pinion retaining nut. An improved type shaft was introduced
for the 1960 models, identifiable by a wider gear. Should wear develop on
the oil pump plunger, the new type shaft should be used.
Crankcase hearings. The bearings fitted to the drive side of the crankcase
are usually trouble free. If a Scrambler Model is used extensively for
racing, or when the power output has been increased by tuning with the
fitment of an ultra high compression piston, a heavy duty roller type
bearing can be used in place of the ball type. The new bearing is of the
Hoffman type RMS 10 (2½" x 1" x ¾") and should be fitted next to the
flywheel. When the bearing is pressed into position, the crankcase should
be peened alongside the outer bearing sleeve in three equi-distant
positions, to keep the sleeve in location,
Timing side bush. It must be mentioned that the outer end (timing gear
side) of this bush is swaged out to make it slightly bell mouth, thus pre-
venting the bush from moving inwards towards the flywheel. This means
that the bush must be extracted by pressure on the flywheel end of the
bush to avoid damage to the crankcase during removal.
Cylinder head and barrel joint. Normally there is an annular space
between the spigot on the cylinder barrel and the small face on the
cylinder, when the cylinder head is assembled. This space can be
eliminated by individual machining, assuming the necessary machining
facilities are available. To do this, machine back the wide face on the
cylinder head, leaving a gap of .001" between the small recess in the
cylinder head and the narrow spigot on the cylinder barrel. Use grinding
paste on the wide face of the cylinder head, also in the small recess. Grind
the head on to the cylinder barrel until both faces on the cylinder head
are mated to the cylinder barrel to give a gas-tight joint. Should an oil
leak develop from the cylinder head face, regrind the spigot situ only.
Dismantling the Scrambler engine. Follow the details given for the
Heavyweight Single Cylinder Models, as the sequence is identical with
the exception of the cylinder head bolts. Check the cylinder head steady
stay for ovality in the bolt holes caused by movement due to looseness,
and get the holes built up by weld and re-drill or replace the stay. Engine
movement due to torque can cause vibration.
Removing the engine from frame. With the cylinder head and barrel, also
piston removed, start by:
Removing magneto case outer cover (see note).
Removing magneto chain with both sprockets.
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