Engine Overhaul of Cummins QSB6.7 in LiuGong 930E Excavator

Engine overhaul of Cummins QSB6.7 (168 kW) in LiuGong 930E excavator

Introduction

The LiuGong 930E crawler excavator is a robust 30-ton machine used in harsh working conditions on construction sites, in mines, and for earthworks. This model is valued for its high efficiency, durability of construction, and precision of hydraulic operation. The heart of the excavator is the Cummins QSB6.7 engine with a power output of 168 kW, meeting stringent emissions standards and providing adequate torque reserve in every situation.

The machine was brought to our WIBAKO service after noticing issues with power loss and excessive smoking. Preliminary diagnostics indicated probable wear of the cylinders and pistons. The client decided to proceed with a full engine overhaul in our workshop, with a final test on the engine dynamometer.

Engine removal from the excavator

The removal of the Cummins QSB6.7 engine was performed on-site at the client's location in the Małopolskie Voivodeship, near Kraków. Our WIBAKO mobile service conducted the complete disassembly using a crane provided by the client. Fuel lines, the cooling system, the air intake, and hydraulic components were disconnected, after which the engine was safely transported to our service center in Kojszówka.

Engine verification

In the workshop, the engine was disassembled into components. The verification process confirmed significant wear of the cylinders, pistons, and rings. Compression was below standard, which explained the earlier symptoms. Additionally, scratches on the sleeves and excessive play in the connecting rod bearings were identified.

As part of the full verification, the following was performed:

• measurement of crankshaft runout,
• checking valve clearances and cylinder head tightness,
• analysis of the injection pump and injectors on the test bench,
• verification of the turbocharger for axial play.

Engine regeneration and repair

The regeneration began with grinding the crankshaft and replacing the bearings. The crank-piston assembly received new sleeves, pistons, and rings. The engine head was machined, and guides and valves were replaced, followed by a leak test in a water bath. The fuel system underwent complete regeneration – the injection pump was checked at a certified facility cooperating with us, and the injectors were recalibrated.

The turbocharger, alternator, and starter were also regenerated. All components were assembled according to Cummins standards, using new gaskets and bolts with the appropriate torque specifications.

Test on the engine dynamometer

After assembly, the Cummins QSB6.7 engine was placed on our engine dynamometer. The tests lasted a total of over 16 hours. In the first phase, the unit operated under light load (20–30% of nominal power), allowing for the observation of pressures and temperatures. After the initial phase, full load tests were conducted – the engine achieved full power of 168 kW, maintaining stable oil pressure and coolant temperature.

Thanks to the WIBAKO engine dynamometer, we can precisely confirm the parameters after the overhaul, avoiding surprises during assembly. This is one of our greatest assets – few service centers in Poland have their own dynamometer for industrial engines, allowing for dynamic testing and torque measurement across the full operating range.

Engine installation in the machine

After a successful test, the engine was reinstalled in the LiuGong 930E excavator. The installation was carried out according to the manufacturer's service documentation. WIBAKO mechanics installed the engine in the drive compartment, connecting all systems – fuel, cooling, intake, and electrical. Air lines, piping, and clamps were replaced with new ones.

Before the first start-up, a leak check and a start-up test were conducted. The engine was started in the presence of the machine operator – after a few minutes of operation, no leaks or irregularities were found. After the tests were completed, an assembly protocol was signed.

Engine maintenance after overhaul

Every engine after an overhaul is covered by a warranty and the possibility of further servicing by WIBAKO. We recommend the first filter change after 50 operating hours and checking the connections between the engine and the hydraulic system. Subsequent inspections are carried out every 250 operating hours or every 3 months. Our mobile service comes directly to the client, providing comprehensive operational support.

Application of the Cummins QSB6.7 engine

The Cummins QSB6.7 engine is found not only in LiuGong excavators but also in many machines from brands such as Doosan, JCB, Hitachi, Volvo, Terex as well as in technological dumpers and loaders. Its popularity stems from the excellent relationship between power, torque, and reliability.

Summary

The overhaul of the Cummins QSB6.7 engine in the LiuGong 930E excavator was a complete success. The machine regained its original power and efficiency, and thanks to the tests on the dynamometer, the client gained confidence that the engine operates correctly. Regular inspections and proper maintenance will ensure high durability of the power unit for thousands of operating hours to come.

WIBAKO offers professional construction machinery service and diesel engine repairs throughout Poland and abroad. We invite you to contact us if you have problems with Cummins engines and other industrial units.

What we do as part of the service

What the repair process looks like