I. Valve leakage
It is possibly caused by:
(1) Wearing, scorching or leakage caused by rough surface (due to corrosion) at the interface between valve and valve
seat. If the working face seal belt of valve seat is worn to be wider than 1.4mm and has spots and pits, it is necessary to
ream and smoothly grind it. If the working face of valve is worn or scotched, you need to grind the working face. If the edge
thickness is less than 0.5mm, you need to replace valve. Whether valve is sealed tight or not can be examined by ways of
light or gas leakage, etc
(2) The valve clearance is too small and disappears after heating. Adjustment of clearance is required.
(3) Carbon deposits too much at the valve seat so that the valve seat is not tightly closed. Cleaning of the valve seat is
required.
(4) In case of bending and deformed valve stem or warped valve head, replace the valve. If the bending of valve stem is
within its allowance, correct it with a manual presser.
(5) If the valve becomes stagnant when moving up and down in the guide or sways inside the valve guide, replace with a
new valve guide. During the replacement, heat the cylinder head uniformly to 80°C to 100°C. Apply engine oil on the exter-
nal wall of the new guide before pressing it into the cylinder head. Meanwhile, it is required to check whether the inner
diameter of valve guide is proper or not. If not, ream it.
(6) If the valve can’t be closed tight due to deformation, replace valve seat ring.
(7) If valve spring breaks or losses elasticity, it shall be replaced.
III. Valve Seat Damage
Common troubles of valve seat are scorching, wearing and deformation. Once any scorching, spots, pits or obvious wear-
ing signs are found in the valve seat, it is necessary to ream or grind it. if it can’t be repaired, replace the cylinder head.
IV. Invalid Valve Spring
A shortened or inelastic valve spring may harm tightness. If the valve spring is not much shortened, it is possible to add
washers on the spring to recover its original length. If it is shortened excessively, replace it. If the spring nearly losses its
elasticity or deviates from upright position for over ?1.2, replace it.
II. Valve Sticking or Scorching
It is mainly caused by extended overload operation of the engine, and insufficient cooling, which wears the valve and
deforms the cylinder head, valve seat and valve guide, thus hampering heat dissipation. Moreover, the high temperature
of the engine leads to the oxidation polymerization and decomposition of lubricant and fuel, which forms gelatinous precipi-
tate at the valve head and valve stem, thus eroding the sealing face of valve. Therefore, leakage and scorching occurs. In
order to avoid this, it is necessary to prevent the engine from extended overload operation. It is also required to clean the
carbon deposit on the valve in the course of servicing.
Section 5 Common Troubleshooting of Valve train
93
Summary of Contents for JL481Q
Page 1: ......
Page 9: ...5 Fig 3 Components Assembly Drawing of MR479Q MR479QA Engine ...
Page 10: ...6 Fig 4 MR479Q MR479QA Engine and Its Power System ...
Page 11: ...7 Fig 5 Assembly Drawing of Engine and Its Auxiliaries MR479Q MR479QA ...
Page 12: ...8 Fig 6 Electronic Control Fuel Injection System in Engine MR479Q MR479QA ...
Page 13: ...9 Fig 7 Front view of Engine JL481Q MR481QA ...
Page 14: ...10 Fig 8 Sectional elevation of Engine JL481Q MR481QA ...
Page 15: ...11 Fig 9 Electronic Control Fuel Injection System in Engine JL481Q MR481QA ...