1. The timing gear assembly mark was incorrectly marked, and the rocker arm broke continuously
After the valve timing gear of a Dongfanghong-60 bulldozer was replaced, the intake valve rocker arm broke. Break failure. After replacing new parts and adjusting the valve clearance, the same failure occurred soon. After careful inspection, it was found that the newly replaced valve timing gear had the wrong assembly mark, causing the piston to collide with the intake valve at top dead center. We used the following method to reassemble the timing gear and the fault was completely eliminated. When installing, do not install the intermediate gear first, rotate the crankshaft to the top dead center position of the I and IV cylinders, so that the two cams of the IV cylinder of the valve camshaft are in an inverted figure, and then install them into the body. Turn the fuel injection pump timing gear to find the fuel supply position of the first cylinder, and then rotate the fuel injection pump timing gear through the corresponding angle in the normal direction according to the fuel supply advance angle (the machine rotates one tooth, which is equivalent to 15? crankshaft angle). Finally, install the intermediate gear, review the valve timing and fuel supply time, and mark it again if correct.
2. The valve clearance changed and the rocker arm broke continuously
A 4115TA diesel engine had its connecting rod, piston, piston ring, and valve parts replaced, and the valve seat was ground. During the test, it ran normally at first, but after running for 30 minutes, the noise suddenly became louder, followed by a ping-pong sound, the diesel engine automatically stalled, and the crankshaft could not rotate. After the failure occurred, the repairman conducted the following inspections and treatments:
(1) Removed the cylinder head cover for inspection and found that the valve rocker arm of the third cylinder was broken, the intake valve was stuck in the valve seat, and the piston was depressed. In the next small pit, half of the valve locking flap is stuck in the pit. Therefore, the repairman replaced the damaged parts.
(2) Start the diesel engine again and run it for about 30 minutes, and the sound changes again. As a result, the pilot immediately shut down the engine.
(3) After disassembling the cylinder head cover for inspection, it was found that the valve rocker arm of the first cylinder was broken again (due to the timely shutdown, other parts were not damaged). At this time, the repairman initially thought that there was a problem with the valve timing.
(4) Check that the timing gear installation marks are aligned, but the inner shaft key of the camshaft gear has become loose and displaced. After the repairman updated the inner shaft key, he started the diesel engine for the third time. As a result, after 30 minutes of operation, the valve rocker arm of the first cylinder broke again.
(5) After careful analysis and repeated searches, the repairman determined that the problem lies in the valve clearance. The inspection found that 4 of the 8 valves have different valve clearances. After re-adjustment is accurate and the machine is tested, check the valve clearance. Unexpectedly, some of the originally adjusted valve clearances have become larger, some have become smaller, and some have even become zero. Therefore, the repairman replaced all the valve adjustment screws, the follower columns and tappets of each cylinder, and the diesel engine was working normally during the test run.
After careful observation of the replaced tappets and follower columns, it was found that the eight tappets were uneven in length due to bending. The ball sockets on the top of the follower columns were not much worn and had different shapes. irregular.
Why do the above problems occur? It turned out that the operator disassembled the tappet and follower column and placed them randomly without marking them. During reassembly, they were not installed according to their original positions. In this way, when the lifter is assembled with an unmatched follower column, the ball head of the lifter and the follower column will sometimes fall deep into the ball socket and sometimes fall shallowly in the ball socket due to the different shapes of the lifter ball head and the follower post, causing the adjustment to be incorrect. The valve clearance often changes, causing the valve to hit the piston and causing the valve rocker arm to break.
3. The camshaft and follower column were severely worn and the rocker arm was broken
A small four-wheel tractor equipped with a JAC 1105 diesel engine
, The valve rocker arm was broken several times, and the last time it caused an engine cylinder crash. After opening the gear chamber cover for inspection, it was found that the gear position of the machine was normal and the oil supply time was normal. The reason for the rocker arm breaking multiple times was that the camshaft and follower column were severely worn, causing the overlapping angle of the valve opening and closing to be too large, and the valve and the follower column were severely worn. The piston struck, breaking the rocker arm. After replacing the camshaft and follower column, the car never had a similar failure again.