Yaroslavl Engine Plant YMZ-536, Operation Manual

Page: 135 / 168

135
VALVE TRAIN CLEARANCE
ADJUSTMENT
Expansion gaps in the valve train are essential to ensure leak-
proof valve contact with the seat during thermal expansion of the
valve train parts when the engine is in operation.
If the clearances are too large, the valve lift is decreased which
results in worse cylinder filling and cleaning, higher shock loads
(valves start knocking) and increased wear of the valve train parts.
If the clearances are too small, the valves do not come in tight
contact with the seats during thermal expansion of the valve train parts
which impairs gas dynamic processes in the engine cylinders and
engine performance. Moreover, decreased clearances of the exhaust
valves can lead to the valves overheating and burning.
Valve train clearances must be adjusted on a cold engine or not
earlier than one hour after the engine was stopped. Valve clearance
adjustment must be performed according to the firing order 1-5-3-6-2-
4. The cylinder numeration begins from the fan.
The clearance between the rocker arm cup and the valve yoke
must be:

for intake valves: 0.30 – 0.40 mm

for exhaust valves: 0.40 – 0.50 mm
The valves located closer to the fan are intake valves; the
valves located closer to the flywheel are exhaust valves.
Valve clearance check and adjustment procedure is as follows:
1. Prepare the driver’s tool kit.
2. Disconnect the gas discharge hose pipe from the cylinder head
cover.
3. Remove the cylinder head cover fixing bolts; then remove the
cylinder head cover.
4. Install the crankshaft turning gear (from the driver’s tool kit) into
the hole (fig. 45) as far as it will go, to engage it with the flywheel
gear. Remove plug 3 located on the flywheel housing end 1 (Fig.
45) on the left engine side under the air break compressor.