After working for a longer period of time, diesel generator sets usually have poor intake and exhaust valve seals, resulting in poor compression. In addition, there is wear on the valve tappet, causing the valve to open for a length of time that is not in accordance with specifications. Valve springs may also break or show signs of softening. Some important parts in the cylinder gasket and valve train such as intake/exhaust valves, cylinders, camshafts, valve springs, rocker arms, tappets, pushrods, etc. may be worn or damaged. When you find that the diesel generator set so with load capacity significantly reduced, you can consider the diesel generator set for overhaul, this top Bo power will tell you the routine procedures of the gas distribution mechanism in the overhaul, the user can repair according to the following methods in an orderly manner.
A, disassemble the cylinder head
(1) After removing the cylinder head from the engine, thoroughly clean the tappet and push rod.
(2) Remove the valve rocker arm mechanism and thoroughly clean each part.
(3) Check for wear at the end of the rocker arm that contacts the valve and pushrod. If there are obvious signs of wear at the valve – end, some rocker arms can be ground to eliminate wear.
(4) Check the straightness of each pushrod. Rolling the pushrod on a flat surface will complete this check.
(5) Carefully inspect the valve guides. Note: Is the clearance between the valve stem and the guide in accordance with the manufacturer’s specifications. If so, some engines have valve guides that can be reamed to the next larger size and then matched with a larger size valve will do the trick.
(6) Remove the valve with a spring-loaded press.
(7) Place the cylinder head in a suitable place so that the reed spring press can be fitted to each valve.
(8) Make sure that the reed spring press is the right size for the valve. Slowly compress the valve springs by levelling the valve spring presser.
(9) When the valve spring is fully compressed, carefully remove the valve retainer and valve spring seat.
(10) Slowly loosen the valve spring press.
(11) Check the end of the valve stem for burrs, which are caused by the rocker arm striking the valve. Carefully remove these burrs with a file before removing the valve. If the burrs are not removed, they may scratch the inner wall of the valve guides and cause the engine to leak oil after reassembly.
(12) Carefully remove each valve and push the valve out of the valve guide.
(13) Thoroughly remove carbon from the cylinder head and combustion chamber. For aluminum cylinder heads, be careful not to damage or scratch the relatively soft aluminum cylinder head.
(14) Use a small punch to remove the more day-old carbon.
(15) Use electric drill and rough wire brush to clean off the carbon on the combustion chamber. Be sure to wear a face shield and goggles during the operation.
(16) Thoroughly remove all carbon from the valves, using a punch to reject larger carbon deposits, being careful not to burr the valve surfaces, especially the rounded areas. Attach a wire brush to the electric grinder and remove the remaining valve carbon, do not use the wire brush to clean the valve stem. Soak the valve in the cleaning agent to soften the remaining carbon and gum, and use polishing grade sandpaper (roughness should not exceed 300) to remove the remaining gum.
Second, check and grind the valve and valve seat
(1) When removing the valve, check the valve cone and valve seat for signs of surface burns
(2) Using a valve grinder, grind each valve according to the manufacturer’s specifications. Most valves are ground to a 44°, 45° or 46° angle, and some engines are ground to a 30° angle, – in general, the processing steps are as follows.
First install the correct grinding stone on the valve grinder, fit the valve in the chuck, and tighten the chuck. Turn on the grinder and move the valve toward the grinding wheel. Make sure the coolant valve is open and coolant can flow onto the valve stem. Slowly feed and grind the valve, making sure the valve does not turn blue. If the valves turn blue, the valves are too hot and too large for one cut. Continue to grind the valve until all erosion points and wear marks have been removed.
(3) After grinding the valve, check the valve thickness and compare it with the manufacturer’s recommended specification. Check the thickness with vernier calipers, the minimum valve thickness is 1/32in, if the thickness is less than 1/32in, this valve can no longer be used and must be replaced with a new valve.
(4) Use the valve seat grinder to grind the valve seat. Follow the tool manufacturer’s step-by-step instructions to properly grind the valve seats. Generally, first install a 45° grinding stone in the sleeve of the valve seat grinder, then insert a guide rod into the valve guide, then place the valve seat grinder and grinding stone on the valve guide and carefully lower it down until it touches the valve seat.
If the manufacturer requires an interference angle, the upper and lower part of the valve seat must be ground with a grinding stone of different angles. When the valve seat must reach the specified width adjustment width, a 30° or 60° grinding stone is used.
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!
