Royal Enfield SPRING FRAME O.H.V. 250cc CLIPPER 1954 Workshop Maintenance Manual page 15

ROYAL ENFIELD WORKSHOP MANUAL
3. Tappet Adjustment
The tappets are adjusted by the ball and
socket joints which are located in a compartment
at the side of the cylinder and access to which is
obtained by removing the inspection cover.
Before checking the clearance or making
any adjustment, rotate the engine until the
piston is at the top of the firing stroke. This will
ensure that both valves are closed and that the
tappets are well clear of the silencing ramps on
the cams. If the cylinder head has been
dismantled, make sure that the end caps have
been put back on the valve stems.
Owing to the ball and socket joints at the
bottom of the push rods, the tappet clearance
cannot be measured there, but between the
valve stems and rockers, with the rocker box
cover removed.
The correct clearance is .002 in. for the inlet
and .004 in. for the exhaust with the engine
COLD.
As a rough guide, the clearance is .002 in.
when the push rod is just free to spin and .004
in. when the up and down play is just
perceptible.
To make the adjustment, hold the push rod
bottom end (top hexagon) and turn the locknut
(middle hexagon) to the left. Screw the push rod
cup (bottom hexagon) to the left to take up
clearance or to the right to increase the
clearance, at the same time holding the push rod
bottom end (top hexagon). Lock the adjustment
by tightening the locknut against the push rod
end and then re-check the clearance.
Owing to the initial bedding down of the
wearing surfaces, the tappets on new engines
may require adjustment after the first few
hundred miles.
4. Ignition Timing
An automatic
mechanism is provided at the back of the contact
breaker, having a range of approximately 121
degrees which corresponds to 25 degrees of the
crankshaft because the contact breaker runs at
half engine speed.
The optimum ignition timing is 30 degrees
advance so that in the fully retarded position the
contact points must open when the piston is five
degrees or 1/64 in. before top dead centre.
Miller Equipment. If the timing drive has
been dismantled, the ignition must be set as
nearly as possible by positioning the cam on the
contact breaker shaft and the fine adjustment
made by rotating the plate on which the contact
breaker is mounted. This plate is held by two
screws in slots in the plate and provides a range
of adjustment of approximately 12 degrees. If
the timing drive has not been dismantled, this
movement will be ample for any small
adjustment required.
Section C3 Page 2
centrifugal advance
To set the ignition timing, remove the
contact breaker cam by taking out the centre
fixing screw using a 5/16 in. bolt as an extractor,
having first checked that the maximum opening
of the points is .015 - .018 in.
Move the contact breaker baseplate until the
screws are in the middle of the slots and tighten
up; then turn the engine until the piston is 1/64
in. before top dead centre on the compression
stroke, i.e., with both valves closed.
Rotate the cam on the contact breaker shaft
in a clockwise direction (looking on the left side
of the engine) until the contact points are just
opening. (See below.)
Give the cam a sharp tap endways to secure
it on the shaft and then lock it tightly with the
centre fixing screw.
Check the timing again and make the final
adjustment by easing the two screws securing
the contact breaker baseplate and rotating it
slightly.
Lucas Equipment. The contact breaker
housing is clamped on to the contact breaker
bracket which is bolted to the top of the
crankcase. The timing is adjusted by slackening
the clamping bolt and rotating the housing
relative to the bracket.
If the timing drive has been dismantled,
clamp the contact breaker housing so that the
name on the cover is roughly horizontal.
Check the maximum opening of the contact
points, which should be .015-.018 in., and adjust
if necessary.
Turn the engine until the piston is 1 in. before
top dead centre on the compression stroke, i.e.,
with both valves closed. (It may be found
convenient to apply the brake to hold the engine
in this position.)
Turn the contact breaker shaft and cam until
the contact points are just opening. (See below.)
Replace the contact breaker pinion and
tighten the fixing bolt.
Having set the timing approximately and
bolted the contact breaker pinion on to the shaft,
check the maximum opening of the contact
points again.
Check the timing again and make the final
adjustment by loosening the clamping bolt
securing the contact breaker housing and rotate
the housing slightly until the correct setting is
obtained.
Contact Opening Point. There are several
methods of determining the point at which the
contacts open:
(l). Switch on the ignition. Looking on the left
side of the engine, rotate the cam in a clockwise
direction (or the housing in a counterclockwise
direction) until the warning light in the ammeter
lights up or until the ammeter needle indicates a
discharge. Continue to rotate the cam (or
housing) slowly until the warning light goes out
or until the