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Maintenance guide: overhaul method of diesel generator set gas distribution mechanism (II)

June 22, 2022
In this article, we will continue to introduce you from three major aspects: inspecting and grinding the valve stem, inspecting the valve guide and inspecting the valve spring.
Three, check and grind the valve stem
(1) Check whether the top of the valve stem is worn by the rocker arm.
a. If the valve stem is not straight, or has a cracked grave, or is out of round, it must be trimmed.
b. Using a valve grinder, first install the grinding stone correctly.
c. Install the valve into the chuck and tighten it.
d. Turn on the grinder and move the valve toward the grinding wheel, making sure the coolant valve is open and coolant can flow to the valve.
e. Slowly feed and grind the valve, making sure the valve does not turn blue; if the valve turns blue, the valve is too hot and the amount of one cut is too large.
f. Continue grinding the valves until all erosion and wear marks have been removed.
g. If the grooves on the valve stem are ground away, the grooves must be re-cut, and the width of the grooves must not exceed 1/32in.
(2) If the valve taper and valve stem are ground, the valve height will be different from the original after installation into the cylinder head. This difference may cause a slight change in valve clearance, especially in overhead camshaft engines. If needed, follow the manufacturer's procedure to check the valve spring mounting height.
IV. Checking the valve guides
Check the valve guides for wear according to the manufacturer's specifications, which are generally listed in the unit's maintenance manual.
(1) Measure the maximum diameter of the valve guide at the end or top of the valve guide's airway.
(2) Insert a telescoping or small-hole gauge into the valve guide.
(3) Remove the gauge and measure its length with a micrometer.
(4) Measure the minimum diameter of the valve stem on the valve, usually the smallest diameter is at the point where the valve stem touches the top of the valve guide.
(5) The value obtained by subtracting these two readings is the valve clearance.
(6) The average specification is 0.001 to 0.003in for intake valves and 0.0015 to O.0035in for exhaust valves. note: these readings may vary with the manufacturer and engine model.
(7) You can also use a micrometer to check the valve guide clearance by placing the micrometer against the valve and moving the valve back and forth to read the clearance value.
(8) If the clearance does not meet the specification, the valve guide should be reamed again.
V. Check the valve spring
(1) When disassembling the cylinder head, check each valve spring for possible fracture and replace if necessary.
(2) Check the positioning and verticality of the valve spring reed by placing the valve spring on a horizontal surface. Place the bottom of the spring against a straight edge as shown in Figure 1. Use a plug ruler or vernier caliper to measure the distance the top of the spring deviates from the right angle ruler, i.e., the clearance. Compare the measured distance with the manufacturer's specifications; the maximum distance allowed may not be exactly the same, but is generally between 1/16 and 5/64in.
(3) To check whether the tension of the valve spring is correct, you can generally use a spring tension tester as shown in Figure 2. After putting the springs into the tester, compress each spring by the same amount. The spring tension tester usually has a limiter on the handle. The tension value is read on a scale and compared to the manufacturer's specifications.
The above is all about the overhaul method of diesel generator set gas distribution mechanism, hope it will be helpful to you!