Perkins L4 Workshop Manual - L-36 Fleet

Page H2 Cylinder Head Maintenance-contlnued
Fig. H2. Checking Yalve Head Clearance and method
of marking valves
lhe spnng becomes weak and is then pro ne to
failure. This, of course, applies to all types of
engines.
A ncw set of springs shouid be fitted whenever
tbe engine undergoes a major overhaul.
Rocker Levers and Bosbes.
Wash the rocker assembly thoroughly in paraffin.
Examine the rocker lever bushes for wear. The
rockers should be an easy fit on the shaft without
excessive side play.
It: as a result of inadequate lubricatioD, aDY
rocker bushes have seized OD the rocker shaft, the
rockers will have worked loose OD the bushes.
Should this have occurred it will be advisable to fit
new rockers andjor bushes.
Should it be necessary to dismantie the rocker
shaft assembly re-assem bie as shown in Fig. H.l.
Valves and Valve Seats.
There will be little wear of the valve sterns or
their guides provided that the lubrication of these
parts has always been adequate.
Examine the valves for cracks. Check wear
of valve sterns and their fit in guides. If the sterns
are wam fit ncw valves.
Number aU new valves to correspond with the
numbering of the old valves.
When fitting new valves take care that the
clearance between the valve head and the cylinder
head bottom face is not less than .057 ins. (1.45 mm)
inlet and .053 ins. (1.35 mm) exhaust. Maximum
clearance should not exceed .140 ins. (3.56 mm)
inlet and exhaust. Check this by putting a straight
edge across the bottom face of the cylinder head
and measuring the distance between the straight
edge and the valve head as illustrated in Fig. H.2.
Tbe efficiency of a diesel engine depends largely
on the maintenance of good compression therefore,
when grinding in valves, make certain thai no
signs of pitting are left on the seatings. Valves
should he ground in until a continuous ., high
mark" is present the full way round the seating,
both on the valve and on the valve seating in tbc
head. At the same time care should be taken to
avoid unnecessary grinding away of the seato .
Valve Guides.
Examine the guides for wear, if necessary replacc
with ncw guides.
To remove oid guides : press out, or uso a suitablc
drift.
To fit ncw guides : clean and remove any hum.
Smear tbc outer surfacc with clean oil, and
using a suitable press, drive home hard
up to the collar. Care should be exercised
as the collar approaches the cylinder head as
the guides arc made of cast iron and therefore
comparatively brittIe.
Cylinder Head.
Remove exhaust manifold and clean off any
carbon deposit formed in the cylinder head.
Wasb out and thoroughly clean tbe water
passages in tbe bead, subsequently drying out and
finally cleaning with compressed air.
If the water jacket of the cylinder head shows
signs of excessive scale, a proprietary brand of
de-scaling solution should be used.
Combustion Chamber Joints.
It is not, as a rele, necessary to remove the
covers of the combustion chambers during a top
overhauI, as carbon rarely fonns in these chambers.
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