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VALVES AND EFFICIENCY
Correct Setting and Timing
Essential
Many faults in engine running often
eau Ibo traced to wong tappet adjust
ment.' Correct setting, using a
feeler gauge, is a simple task, and,
done at. regular 'intervals, will ''guaran
tee bettor .and more economical run
ning.
TC 'both sets of valve stems nra tight
on the tappets, compression iv ill (be
poor, starting difficult and pulling bail;,
in addiliion, the eugine 'will tend to
overheat.
Insufficient, inlet-valve clearance wi'll
cause 'blowing «nek in tili rs carburetter,
and consequent petrol waste, but if
the 'exhaust valves cannot seat properly
their heads will bo burned, and possibly
the seatings will warp.
However, there is one point, wilipili
should 'ho 'borne in mind iby owners
of the less expensive types of car. 'Small,
but often appreciable, variations in tho
theoirelica'lly correct opening aird 'dos
ing points of the valve may occur
owing lo sliglit inai'i'iiracies in Hie eoni
din pcs or in the rockers. It will bo
iippi'dcia'tod Clint an absolutely 'perfect
(?aini-shad't is extremely expensive to
produce, and is a practicable proposi
tion only on .tho very highest class en
'gines. Tihe valve-operating mechanism
on normal engines is accurate enough
for all practical purposes, but iii' the
exact opening and closing points .at the
valves be checked .against itlho crank
angles it will 'be found .sometimes that
they do not agree with the makers'
Urning diagram.
The test. must, ibo made, 'of course,
wit* tho 'tappets adjusted to the cor
rect clearance, .'ind il. is 'hore than an
alteration in Hie liming can ibo anade
it' necessary.
Il jot Us suppose lihat tho inlet valves
should begin to open exactly on the to|:
dead centre, ililli, Hist; a test Shows itlieih'
'to Ibo opening, say, three degrees he
fore t.'d.e. Ey increasing Hie tappo!
clearanco an extra thousandth of. ai
inch or so tho discrepancy cati ge vor
reeled, and the additional cleao-anci
need cause no concern, ¡because.it i:
far botter to lose 'a '' thou." on thc Hf
of Wie valves an-d liavo the timing coi
reel, -Ulmn vico versa.
The exhaust valve timing Will als
pay for tren I nient in this way, and it ii
i Import ail t to remember IMi'at. the mos
crilical point in the cycle of operation
.in a. petrol engine is that af, which th
oxhaust valve closes .ind the inlet open
round about top dead centre. Tho opei
img of the exhaust before b.d.c. an
the closing nf the inlet after ib.d.e. an
within 'limits, not. nearly so iinpor
ant.
The valves «I" each cylinder slioul
ho checked 'in turn at. the t.d.c. pos
tioiis, .1)111. it' the timing 'is out. on iii
wrong side-Ural, is, iii' a. smaller |..i|
pot clearanco than that recominendc
is noodi-d to make it correct-then it :
better to lut well alone and thus avoi
tho risk of ¡burned valves. 'Turning ci
tlmsiaats should remember that thc
cannot limprovo 'Uho liming .hy r
meshing tho timing wheels.
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