FAW Jiefang Automotive 485, Руководство по эксплуатации и техническому обслуживанию

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because valve guide wear-off can lead to partial grinding of the sealing surface, causing poor
sealing. After grinding is done, pour some kerosene or diesel oil into the air-way, to see if the
valve leaks and check for its tightness.
Normal width of the sealing surface between valve and valve seat is 1.2
～
1.7mm. After it has
been used for long time and ground for more times, the sealing surface can become wider, causing
poor sealing. Therefore it is necessary to use 15
°
and 75
°
reamer separately, to scrape and trim
it as per the positioning of inner-hole of valve guide, as shown in Fig.3. After the scraping,
pair-grinding with valve is again necessary.
The deflected distance between intake/exhaust valve plane and cylinder cover plane is 0.55
～
0.85mm for a new engine, as shown in Fig.4. After scraping and trimming for several times, the
distance will increased and thus will influence the compression ratio. Therefore, the valve seat
may necessarily be replaced, if the deflected distance is increased to be 2mm or more.
Fig. 3 Trimming of valve seat Fig.4 Deflection of valve
The valve guide, when assembled, should be 12.5
～
13mm higher than the plane of cylinder
cover.
It is necessary to often inspect the valve lash or clearance. For its adjusting method please see
Section I, Chapter X. Incorrect clearance will influence the accuracy of valve timing and
tightness of valve. Additionally, too big clearance will lead to more noise of valve driving device,
and too small clearance will lead to an un-tight closing and burn-out of the valve.
2. Cylinder cover gasket
The gasket should be flat and smooth. Gaskets with defects such as warp and burn should be
replaced.
When the piston is at top dead center, there should be a clearance between the top of piston
and bottom plane of cylinder cover, to prevent the compression ratio from being influenced or the
valve from being collided by the top of piston.
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