Valve Clearances; Compression Pressure; Oil System - Mitsubishi 4DQ50 Service Manual

2-3 Valve clearances
Both lack and excess of valve clearances affect engine performance. Especially-
excessive valve clearances will induce much strain. on valve mechanism, making the
engine subject to serious trouble.
Apart from regular checking required every 2S0Hr of run, check and adjust them
whenever low-speed running of the engine makes any unusual sounds. For new Engine,
adjust them when it has run for 60Hr. Proper clearances are, exhaust and inlet valves
alike, O.2Smm as measured in cold (or uniformly warm) engine.
Firing order is: 1-3-4-2.
2-4 Compression pressure
1) To see whether or not intake air into cylinders undergoes there sufficient
compression with no blow-by to help the firing, measure compression pressure.
2) The results will tell if:
a) Valve seats are in tight enough contact.
b) Cylinder liners and piston rings are not worn or sticking hard.
c) There is any leak of gas ascribable to other cuases.
Regular measurement at intervals of about SOOHr of run will provide reliable data
to decide when to overhaul the engine.
3) Prior to measuring it, check
and adjust valve clearances so
that rockers do not press down
valves in compression stroke,
and make sure that Venturi
butterfly valve is full open.
4) Standard compression pressure
is above 20kg/cm
2
at an engine
speed of 1S0-200 r.p.m., and
with oil and water tempera-
tures in a range of 20°-30°C.
Fig.3-10 Adjusting valve clearance
Please have it measured by your dealer or at a service shop.
3 OIL SYSTEM
As can be seen in circulation diagram (F ig. 3-11), lubrication system is forced
lubrication by a trochoid oil pump. At option, a water-cooled oil cooler is equipped between
oil pump and oil filter to keep oil in an optimum temperature range.
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