Diagnosis and regeneration of the Cummins QSB4.5 engine in the JLG G10-55A loader

Introduction

The WIBAKO service received a JLG G10-55A telehandler with a Cummins QSB4.5 (Tier 4 Interim) engine. The machine had been working on construction sites in the Małopolskie Voivodeship, and in recent weeks the operator reported increasing difficulties with starting, hard work under load, and increased smoking during acceleration. The owner approached us for a full diagnosis and possible repair of the power unit. As a specialized off-highway machine service, we provide a comprehensive approach: initial mobile diagnostics, disassembly and assembly of the engine in the machine, complete workshop rebuild, and load tests on our engine dynamometer.

The machine manufacturer, JLG, is one of the leading suppliers of telehandlers and aerial work platforms, where reliability and equipment availability directly translate into timely work. Meanwhile, the Cummins brand is a global synonym for durable and economical diesel units, and the QSB4.5 series consists of compact engines with high torque, commonly used in construction and agricultural machinery. In the Tier 4 Interim version, the exhaust cleaning system has been expanded according to emission standards, which requires precise diagnostics and professional service.

The initial assessment at the customer's site indicated damage to the injection system: uneven, hard work, increased fuel consumption, and dark smoke during rapid acceleration. These symptoms often result from improper fuel atomization or injector calibration issues, but they can also accompany secondary damage to mechanical components. To confirm the diagnosis and rule out coexisting faults, we planned a full sequence of actions from measurements on the machine, through verification in the workshop, to testing on the dynamometer.

Initial diagnostics in the machine

Our WIBAKO mobile service team arrived at the machine's work site near Krakow. We conducted basic measurements: checking the fuel supply pressure, preliminary compression test with recording of the starting speed, reading operating parameters and controller errors. We then performed smoke analysis and checked operating temperatures. The fuel pressure values were unstable, and the injection dose corrections significantly deviated from nominal values. To confirm, we conducted a cylinder cut-off test and examined the returns from the injectors. The results clearly suggested improper operation of at least two injectors with a risk of fuel contamination.

Due to further risk of damage and the need for thorough verification, we decided to disassemble the engine and transport it to our headquarters in Kojszówka. During this visit, the technicians also inspected the intake and cooling systems to rule out secondary factors such as leaks in pressure lines or airflow restrictions.

Engine disassembly from the machine

The disassembly was carried out in accordance with safety procedures and manufacturer recommendations. The engine disassembly is always performed using a crane provided by the customer. After properly securing the work area, we disconnected the batteries, cooling system, fuel and return lines, electrical installation, and the intake and exhaust systems. We removed the accessories that could hinder the safe removal of the unit, including the alternator, starter, and elements securing the lines. All open ports of the systems were sealed to prevent contamination from entering. After releasing the engine mounts and disconnecting the connection to the gearbox, the unit was lifted and transferred to a prepared transport pallet. In accordance with WIBAKO standards, we prepared photographic documentation and a disassembly protocol to facilitate later assembly and verification of additional work.

The engine was transported to our workshop in Kojszówka, where it entered the clean disassembly zone. During this time, the machine was secured and prepared for later assembly, including closing the systems and arranging the harnesses to minimize the risk of damage during downtime.

Engine verification in the workshop

After preliminary washing and disassembly of the accessories, we proceeded to disassemble the core of the unit. The verification included detailed measurements of the crankshaft, inspection of connecting rods, pistons, cylinder liners, and bearings, as well as checking valve clearances and cylinder head tightness. In the fuel system, we disassembled the high-pressure pump and injectors. Preliminary inspections confirmed damage to the injection system and the presence of metal shavings that may have penetrated the fuel rail. Additionally, we noted increased wear of the piston rings on two cylinders, which explained the slightly reduced compression test result.

The cylinder head underwent a leak test in a water bath with compressed air, which allowed us to rule out micro-cracks. The crankshaft underwent visual inspection and journal measurements, and the oil channels were thoroughly cleaned. The turbocharger was checked for axial and radial play, and no irregularities requiring its replacement were found. The conclusion from the verification was the necessity for comprehensive regeneration of the fuel system, refreshing the connecting rod-piston system, and full service of the cylinder head.

Regeneration and repair

Connecting rod-piston system

As part of the work, we replaced the cylinder liners, pistons with rings, and main and connecting rod bearings. The connecting rods were checked for twisting and longitudinal bending and weighed to maintain the balance of rotating masses. We cleaned the oil channels with the utmost care to eliminate the risk of leaving contaminants after the fuel system failure. The crankshaft, after measurements, was within the norms, so we limited ourselves to polishing the journals and thoroughly flushing the oil channels.

Engine head

The cylinder head was planed, we replaced the guides and valves, created valve seats, and set the appropriate clearances. The leak test after machining confirmed the correct parameters. The water and oil channels were cleaned in chemical washers, and the components were reassembled using new high-quality seals.

Fuel system

The injectors were placed on the test bench and underwent full calibration. We replaced components that did not meet the parameters with regenerated ones with confirmed characteristics. The high-pressure pump was regenerated at an external specialized facility and delivered with a testing protocol. The high-pressure lines and common rail were flushed and inspected, and the fuel filter along with the housing was replaced. We ensured the fuel supply source: the tank was cleaned, and the system was bled and checked for tightness to eliminate the risk of returning metal shavings.

Accessories and preparation for assembly

We performed an inspection of the turbocharger (play within the norm), starter, and alternator, replaced belts and pulleys of the accessory drive, and assessed the water pump and thermostat as functional. All static and dynamic seals were replaced with new ones. After closing the unit, we proceeded to adjustments and preliminary settings according to the technical documentation.

Test on the engine dynamometer

Every engine after repair at WIBAKO undergoes a full load test on the engine dynamometer. This is a key element of the process, allowing us to verify not only performance but also stability of operation, tightness of systems, and proper fuel calibration. Our dynamometer allows control of parameters over a wide range of loads and rotational speeds, as well as recording temperature, pressure, and flow profiles. We start the test by running under light conditions, usually at 20-30% of nominal load. For a minimum of 16 hours, the unit operates at various points of the characteristic, allowing new components to bed in without excessive loading. During this time, we monitor the temperature of the coolant, oil, pressure drops on the filters, boost pressure, injection corrections, and uniformity of cylinder operation.

After the initial phase, we move on to a series of full and transitional loads. We check whether the engine achieves the assumed power and torque parameters, as well as how it reacts to rapid changes in load. It is essential to maintain proper dynamics of pressures in the fuel system and stable operation of the turbocharger. We pay attention to the working culture and vibration levels, which may indicate previously unseen irregularities. Since the QSB4.5 in the Tier 4 Interim specification works with an exhaust emission reduction system, we monitor temperatures in the exhaust system and mixture parameters to ensure proper working conditions for the exhaust cleaning components. Equipment versions may vary, so we adjust the tests to the specific configuration of the machine's accessories.

Closing the dynamometer stage, we perform a tightness check of the oil, fuel, cooling, and intake systems. If all parameters are normal and the profiles are stable, we issue a test protocol, which is attached to the documentation. Such a test gives the owner assurance that the engine will return to the machine in full working order, reducing the risk of downtime and additional costs after assembly.

Assembly in the machine

After positive dynamometer tests, the WIBAKO mobile service team carried out the assembly of the engine in the JLG G10-55A loader on the customer's site near Krakow. The assembly process was preceded by preparing the workstation, verifying the availability of the crane provided by the customer, and checking the condition of the mounts and pads. We introduced the unit into the chamber, ensuring proper routing of harnesses and lines and maintaining tightening moments in accordance with the documentation. We made new fuel connections, paying special attention to the cleanliness of the joints after the previous injection system failure. The cooling system was filled with fresh fluid and bled, and rubber hoses were inspected and replaced where signs of aging were found.

The air intake was assembled with new clamps and seals. We used new air and fuel filters, and positioned the fuel filter housing according to the flow direction and manufacturer recommendations. The exhaust system was assembled without stress and checked for leaks. We conducted thorough inspections of the electrical harnesses, improved the routing of wires in areas prone to abrasion, and protected them with thermal shields near hot components. After filling the engine with oil that meets Cummins specifications and after preliminary leak tests, we proceeded to the control start-up.

The first start-up took place in the presence of the customer's operator. We recorded operating parameters, checked oil pressure, temperatures, and injection correction values. We then conducted a series of functional tests: lifting and extending the arm, driving with varying loads, and hydraulic work cycles. Together with the operator, we assessed the machine's response to the throttle, working culture, and absence of smoke. Each of the systems connected to the engine was checked for tightness. After several hours of testing and no leaks, we signed the assembly protocol, and the machine was approved for operation.

Service and recommendations after repair

WIBAKO delivers engines after repair with a warranty and offers ongoing service. We recommend the first filter change and inspection after 50 operating hours from start-up. During this inspection, our mechanics not only replace fluids but also review the connections between the engine and other components, verify the tightness of systems, and check the operating parameters of the unit. Subsequent inspections are planned every 250 operating hours, but no less than every 3 months. This allows us to maintain stable operating conditions and prevent minor failures that could lead to costly downtimes.

After repairing the injection system, we pay special attention to fuel quality and regular filter changes. We also recommend periodic inspection of the fuel tank and venting, especially in machines operating in dusty conditions. We remind operators of the necessity to warm up the unit before intensive work and to cool it down after heavy loads, which extends the durability of the turbocharger and exhaust system components.

In which machines does the Cummins QSB4.5 engine occur

The Cummins QSB4.5 (Tier 4 Interim) is a unit widely used in the off-highway segment. It is found in selected models of telehandlers, wheel loaders, agricultural and industrial machines. Depending on the version of the accessories, it can work with various exhaust cleaning systems. Example applications include JLG telehandlers in the 10-12 ton lifting class, as well as selected machines from manufacturers such as Genie, SkyTrak, Case, or New Holland in appropriate equipment versions. In case of doubts about the compatibility of a given model with a specific version of QSB4.5, our WIBAKO technical department verifies serial numbers and execution specifications before proceeding with work.

Summary of benefits for the customer

The comprehensive WIBAKO service, including diagnostics, disassembly, repair, and dynamometer testing, restored the JLG G10-55A loader to full functionality. The owner gained a unit with parameters confirmed by the dynamometer protocol, a regenerated injection system, and a refreshed connecting rod-piston system and cylinder head. Through preventive replacement of filters, fluids, and seals, we reduced the risk of secondary leaks. Professional assembly and joint tests with the operator allowed for a quick return to work on the construction site without unnecessary downtime.

If the machine operates in an intensive cycle, and symptoms such as difficult starting, smoking, or loss of power begin to intensify, do not wait for more serious consequences. Contact WIBAKO and schedule diagnostics. We operate mobile in the Małopolskie, Silesian, Świętokrzyskie, Opole, and Łódź Voivodeships, and transport engines to our headquarters in Kojszówka. In selected cases, we also carry out orders in the border region of Slovakia and the Czech Republic.

Supported machine brands

WIBAKO specializes in servicing machines from manufacturers such as: JLG, Genie, Manitou, JCB, Caterpillar, Volvo, Komatsu, Liebherr, Doosan, Case, New Holland, Sennebogen, and others. We offer construction machinery service and Cummins diesel engine service and many other brands, providing comprehensive rebuilding based on our quality procedures, engine dynamometer, and mobile service teams.

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See also

Cummins engine repairs | Injection system diagnostics | WIBAKO engine dynamometer | Mobile service | Parts for QSB engines