Eliminate resonance noise of excavator accessories

2025-03-19

Two CAT950B loaders experienced severe engine oscillation when starting from scratch after repairing the connecting rod bearings of the engine. One of them presented a severe situation where the air filter and muffler were shaken off, and the vibration damping block was cracked.

This model is equipped with CAT3304 engine. As it only has 4 cylinders, a dual balancing device is installed to balance the inertia force generated by the crank connecting rod mechanism due to the large work interval. When installing, it is necessary to strictly ensure that all marks on the timing gear and the balance crankshaft gear are aligned one by one. Only in this way can the inertia force of the engine be balanced. Ensure smooth operation of the engine. According to the structure and repair process of the machine, the problem is caused by the imbalance of inertia force in the engine crank connecting rod mechanism. During maintenance, the oil pump was removed, but during installation, the timing gear chamber cover was not opened to match the markings one by one (the markings could not be seen) before being reinstalled. As a result, the double balance shaft failed to balance and caused engine oscillation.

The oil pump gear is the central gear between the crankshaft gear and the balance shaft gear. After opening the cover of the timing gear chamber and aligning it with the markings on the timing gear and balance shaft gear, the problem was resolved during the test run. But if the timing gear chamber cover needs to be removed and marked just to inspect the crankshaft or oil pump, the workload is really too much. We have explored a simple method and now introduce it as follows:

(1) Find the tightening top dead center of cylinder I: Insert the timing bolt into the hole on the flywheel housing and press it towards the flywheel. Roll the crankshaft counterclockwise until the timing bolt penetrates the hole on the flywheel and presses against it. Roll the crankshaft counterclockwise until the timing bolt penetrates the hole on the flywheel, then stop rolling. Remove the valve cover and check the two valves of cylinder I. If the piston of cylinder I is at the top dead center of the tightening stroke, both valves should be closed. At this moment, the rocker arm can be pulled up and down by hand. If the rocker arm cannot be moved, remove the timing bolt from the flywheel and roll the crankshaft 3600 counterclockwise. And install the timing bolt, which is now the top dead center of the tightening stroke of cylinder I. If the timing bolt penetrates the flywheel and the timing cover of the high-pressure oil pump is removed, the timing pin can be inserted into the cam groove of the fuel injection pump, and it can also be determined that cylinder I is at the top dead center of the tightening stroke at this moment.

(2) At the bottom of the engine crankcase, there are bolt holes on both ends of a large tile in the center. Roll the balance shaft by hand, and when the concave part of the shaft aligns with the bolt hole, screw in the bolt to press against the concave surface of the balance shaft, preventing it from rolling.

(3) After positioning the crankshaft and balance shaft, install the oil pump without aligning the markings. Finally, remove the bolts that position the balance shaft.

After installation in this way, both engines worked smoothly and oscillations were eliminated.