Geely JL481Q, Руководство пользователя

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The greatest wear of the piston is the wear of the piston ring slot. Due to the pressure of the cylinder, the piston ring applies
a high pressure on the slot. Under the action of a high temperature and pressure, the first ring slot is worn most severely,
and the wear of the following ones decreases gradually. The clearance between the piston ring and the wall of the ring slot
can be measured with a thickness gauge. Ring slot clearance: permissible for the first slot: 0.020-0.055mm, for the second
slot: 0.020-0.055mm. In the case of the clearance being greater than the max., replace the piston. Furthermore, as wear is
likely between the piston pin and the pin hole, causing a loose engagement between the two. In the case of abnormal
noise, if the piston can move back and forth on the piston pin, then, replace the whole set of piston and piston pin
In the case of small metallic chips existing between the piston and the cylinder wall, high temperature caused by friction
makes such chips contact each other, and the relative movement cuts off the thermo-welded locations so that the friction
surface becomes rough and galling scratches appear. Among the causes for the galling are: a. Ineffective sealing of the
piston ring leading to increased leakage, overheated piston and damaged oil film. b. A narrow galling surface in the middle
of the main thrust surface indicates an excessive ellipticity. If there are wide galling surface in the middles of both thrust
planes, that indicates that the cylinder play is too small. c. If the galling takes place at the four 450 diagonal locations of the
center line of the piston pin, that indicates that there is a too tight match between the piston pin and the pin hole.
Serious galling or extremely poor piston lubrication is likely to lead to ablation. In such cases, replace the entire set of piston
assembly.
II. Damage of the Piston Pin
III. Broken or Ablated Piston Ring
Table 6
Among common faults with the piston pin are tubercular corrosion, fleck and bending deformation due to wearing as well
as deformation of out-of-round. If the cylindricity of the piston pin is over 0.002mm and roundness is over 0.0015mm, then
replace the piston pin.
Common faults with the piston ring are break, wear, ablation and burr. When its end play or side play is too small, or the
frequency of its radial bouncing is not consistent with the natural frequency of the ring, the piston pin is likely to break.
Measure the end play and side play of the piston pin with a thickness gauge. For check of the end play, push the piston ring
into the cylinder at a position 97mm from the top of the cylinder block. Detailed data are given in the table below. In the case
of a too small end play, use a fine file. For check of the side play, install the piston ring to the piston. In the case of a too
small side play, adjust it by fine polishing. If the combustion chamber has an excessive temperature, engine oil glues, or
the cylinder has a poor lubrication, then, the piston ring is prone to ablation. See Table 6 for the maintenance data for the
piston ring.
First one
Second one
First one
Second one
Oil ring
First one
Second one
Oil ring
Standard
Standard
Max
Gap of the piston ring slot
Opening gap of the piston ring
MR 479Q,MR479QA
(within 78.70)
MR481QA,JL481Q
(within 81)
Name
Maintenance data
Maintenance data for the piston ring
1.05mm
1.20mm
1.10mm
0.2-0.5mm
In the case of piston deformation, just measure the ellipticity of the skirt of the piston 18mm (MR479Q)/16mm
(MR479QA) /20mm (MR481QA,JL481Q) from the piston bottom, in a direction vertical to the pin hole). If the deviation-
from the standard value exceeds 0.04mm, replace the piston.
0.020-0.055mm
0.2-0.4mm
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