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ROYAL ENFIELD 350cc and 500cc O.H.V. WORKSHOP MANUAL
the rate of loss past the rings will increase, so that the
oil consumption in a well worn engine may increase
to 800-1,000 m.p.g. If the oil consumption is heavier
than this (or is heavier than 1,500-2,000 m.p.g. in an
engine having a cylinder and piston in good
condition) the cause of the excessive loss of oil
should be examined. The following are the most
likely causes :
1. External oil leaks which may occur at any of
the joint faces and are cured by remaking the
joint.*
2. A partial obstruction in either suction or
delivery passages leading to and from the
return pump.
3. An air leak on the suction side of the return
pump. Such a leak can occur at the washer
beneath the front gauze filter, at the timing
cover joint face where the suction passage
crosses it, at the seating of the return pump
disc in its housing or between the return pump
plunger and its cylinder.
The effect of any defect in the return pump
system is to allow oil to accumulate in the flywheel
chamber and to escape past the driving side main
bearing and through the crankcase breather which is
situated behind the primary chain case. Any excessive
amount of oil leaking at this point should therefore
immediately suggest a defect in the return system.
(Note that a certain amount of oily vapour will
normally be blown out of the crankcase breather.)
To test the fit of the return pump plunger in its
cylinder, remove the pump cover plate and lift out the
pump disc and plunger. The fit of the plunger can be
tested by placing a finger over the middle hole in the
lower face of the disc and pulling the plunger out
quickly. The plunger should be a good enough fit in
the cylinder to spring back when released.
25. Replacing Pump Discs.
If the underside of the pump disc or the face
against which it works shows signs of dirt or scoring,
the disc should be relapped on to its seating, using fine
pumice powder and oil or metal polish. Fig. 27 shows
TOOL FOR LAPPING PUMP DISCS
*NOTE.-Excessive oil leaks from the push rod enclosure tube
joints, tappet chest, exhaust valve lifter adjusting bush or the back
of the timing cover, may be due to too much oil being pumped to
the rocker gear. This can be checked by replacing the external pipe
leading to the rocker gear by a pipe connected to a sensitive
pressure gauge, which should record a pressure of about 2 lbs. per
sq. in. when the engine is running. To reduce the head of oil, fit a
washer beneath the head of brass plug securing the ball valve
spring (see Fig. 26). To increase the head of oil, remove any
washers already fitted or remove the plug and spring, stretch the
latter and replace.
Page 18
Fig. 27
suitable tool for lapping the disc. This can be held in
the chuck of a brace. If a new disc is fitted it will be
found that the top surface is completely circular. After
lapping the disc, the flat face up the side must be
continued right to the top, otherwise the driving pin
on the end of the cross shaft will foul the disc.
Examine the lower face of the return pump disc for
signs of it having been lifted off its seating by
endways movement of the driving shaft and, if
necessary, file a little extra clearance at the corner of
the disc where the shaft may foul it.
When fitting a new feed pump disc, make sure
that it never simultaneously covers both the ports N
and Z (see Fig. 23). If necessary, file a little more off
the flat up the side of the disc to ensure this.
When replacing either pump disc make quite sure
that there is no dirt between the lower face and the
housing and see that the small coil spring is in
position between the top of the disc and the pump
cover plate. The joint beneath the cover plate must be
air and oiltight.
26. Draining the System.
To drain all oil out of the engine remove the filter
plugs C and F (Fig. 25) and the feed plug D (Fig. 25)
leaning the machine to the right to empty the timing
case. Remove also the felt element from the oil filter
L (see Fig. 28 for details).
DETAIL OF FELT OIL CLEANER
The oil should be changed after the first 500
miles and subsequently every 2,000 miles. All filters
must be cleaned whenever the oil is changed and the
felt filter element replaced every 5,000 miles.
Note.-After replacing the felt filter element allow
the engine to tick over gently for five minutes to
replace the oil in the filter housing. The big-end does
not receive any oil until this has been done.
After draining the timing case the oil level in the
tank will sink rapidly until the oil level in the timing
case has been made up to normal.
Fig. 28
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