# Repair of the Cummins QSB 4.5 Engine in the JLG 1055 Telehandler

> The overhaul of the Cummins QSB 4.5 engine in the JLG 1055 telehandler is a comprehensive process that includes diagnostics, disassembly, component verification, and testing on a dynamometer. Discover how we restore the engine's power and efficiency, ensuring its long-lasting performance.

## Cummins QSB 4.5 Engine Overhaul in a JLG 1055 Telehandler

A JLG 1055 telehandler cannot afford long downtime[cite: 1]. When the engine starts losing power, running unevenly, and clearly straying from its factory specs, continued operation can quickly turn into a major failure[cite: 1]. In the case of this machine, the issue involved the **Cummins QSB 4.5 engine**, requiring a thorough diagnostic process followed by a comprehensive overhaul of the power unit[cite: 1].

The JLG 1055 is a telehandler built for demanding tasks where both adequate power and smooth engine response to load changes are essential[cite: 1]. The Cummins QSB 4.5 is a diesel engine used in many construction and industrial machines[cite: 1]. The design of this engine allows it to operate under harsh conditions; however, natural component wear or improper operating conditions can still lead to a loss of performance[cite: 1].

In this case, we decided to perform a complete overhaul of the Cummins QSB 4.5 engine[cite: 1]. The work included diagnostics while the unit was still in the machine, engine removal, thorough inspection of all key components, repair of the crank-piston assembly, head and accessory checks, professional assembly, and a load test on an engine dynamometer[cite: 1]. Only after successfully passing these tests was the engine prepared for reinstallation into the JLG 1055 telehandler[cite: 1].

### Initial Diagnostics of the Cummins QSB 4.5 Engine in the JLG 1055

We begin every engine overhaul by identifying the root cause of the problem as accurately as possible[cite: 1]. Removing the engine without prior diagnostics would mean losing crucial information about its behavior under actual operating conditions[cite: 1]. Therefore, before removing the Cummins QSB 4.5 from the JLG 1055 telehandler, our mechanics carried out basic in-machine diagnostics[cite: 1].

For this telehandler, the reason for the overhaul was **natural engine wear due to high operating hours**[cite: 1]. Symptoms of gradual engine wear can initially be relatively easy to overlook[cite: 1]. The engine still starts and allows the machine to work, but over time, a noticeable loss of power occurs, oil and fuel consumption increase, and load response becomes sluggish[cite: 1].

First, we checked engine behavior during startup[cite: 1]. It was essential to determine whether the unit starts correctly and maintains a stable idle speed afterward[cite: 1]. Next, we observed engine operation across various RPM ranges and while applying load to the machine[cite: 1]. This made it possible to evaluate whether the issue was limited to a specific operating range or was more general in nature[cite: 1].

Key operating parameters were also inspected[cite: 1]. We checked oil pressure and the performance of the lubrication system[cite: 1]. An important part of the diagnostics was evaluating the intake and exhaust systems, as well as inspecting the accessories working alongside the engine[cite: 1]. For an engine with many operating hours, diagnostics cannot be limited to a single component[cite: 1].

The next phase was diagnostic testing to confirm the extent of engine wear[cite: 1]. Measurements taken and operational observations indicated that the problem was mechanical and could not be resolved with simple adjustments or by replacing a single accessory[cite: 1]. Consequently, we decided to remove the Cummins QSB 4.5 and conduct a complete engine inspection in our workshop[cite: 1].

### Removing the Cummins QSB 4.5 from the JLG Telehandler

Following initial diagnostics, we prepared the JLG 1055 telehandler for engine removal[cite: 1]. Removing a power unit requires a strict sequence of actions—it is not just a matter of unbolting the engine mounts[cite: 1]. Prior to removal, all wiring, lines, and hoses must be properly disconnected, and the components remaining in the machine must be secured[cite: 1].

The Cummins QSB 4.5 engine was prepared for extraction from the engine compartment[cite: 1]. Electrical connections, cooling lines, intake components, and lines necessary to safely separate the engine from the rest of the telehandler's subassemblies were disconnected[cite: 1]. Special care was taken to protect intake and cooling system components from contamination[cite: 1].

To lift the engine, we used a **crane provided by the client**[cite: 1]. Once properly prepared, the Cummins QSB 4.5 unit was suspended and maneuvered out of the JLG 1055 engine bay[cite: 1]. Mechanics monitored the entire process to prevent stress on hoses, electrical cables, or other components remaining in the machine during the lift[cite: 1].

Once removed, the engine was secured and prepared for transport to our main facility in Kojszówka[cite: 1]. There, the main phase of the overhaul began: teardown and detailed inspection of the Cummins QSB 4.5 components[cite: 1].

### Engine Inspection of the Cummins QSB 4.5 in the Workshop

After the engine arrived at our workshop, we began teardown[cite: 1]. For a unit classified as requiring an overhaul, the engine is completely disassembled into individual components, which are then thoroughly washed and inspected by mechanics[cite: 1]. This approach allows us to evaluate the actual condition of the engine rather than relying solely on symptoms observed during operation[cite: 1].

First, we evaluated external components and prepared the unit for further disassembly[cite: 1]. We then worked through the engine step by step, inspecting parts for signs of wear, overheating, mechanical damage, and improper interaction between subassemblies[cite: 1].

The **crank-piston assembly** was inspected with particular care[cite: 1]. We checked the condition of the crankshaft, connecting rods, pistons, rings, cylinder liners, and bearings[cite: 1]. The crankshaft underwent visual inspection as well as precise measurements[cite: 1]. Journal dimensions, runout, and the condition of oil galleries were checked[cite: 1]. These measurements determine whether the crankshaft can be reused or requires reconditioning[cite: 1].

Connecting rods were evaluated for wear, cracks, signs of overheating, and deformation[cite: 1]. Their dimensions and bolt conditions were also verified[cite: 1]. Pistons and rings were checked for wear, while cylinder liners were inspected for working surface condition and dimensions[cite: 1].

The cylinder head was also subjected to detailed inspection[cite: 1]. We checked the condition of valve seats, valves, and valve guides[cite: 1]. The head requires careful checking because even minor sealing issues can affect overall engine operation[cite: 1]. As part of the inspection, head leak testing is performed by submerging the head in heated water and applying compressed air, allowing us to detect any hidden cracks or leaks[cite: 1].

We also inspected the camshaft[cite: 1]. Inspection includes a visual assessment as well as dimensional checks of journals and lobes for wear[cite: 1]. The turbocharger required separate verification, focusing primarily on axial and radial play[cite: 1].

This thorough inspection confirmed that the cause of the issues was progressive operational degradation of internal engine components[cite: 1]. The condition of individual parts indicated the necessity of a comprehensive overhaul rather than limiting repairs to a single damaged component[cite: 1].

### Crank-Piston Assembly Overhaul for the Cummins QSB 4.5

The most critical part of the overhaul involved the crank-piston assembly[cite: 1]. The harmonious interaction of the crankshaft, connecting rods, pistons, rings, liners, and bearings determines the proper transfer of combustion energy to the machine's powertrain[cite: 1].

After thorough cleaning, every single component was subjected to dimensional measurements[cite: 1]. The crankshaft was checked for journal wear and runout[cite: 1]. For components requiring reconditioning, the scope of work is tailored to the actual condition of the part[cite: 1]. Reconditioning the crankshaft involves grinding the journals to specification and fitting correctly sized matching bearings[cite: 1].

Connecting rods, pistons, and cylinder liners were also verified[cite: 1]. In an engine with high operating hours, one cannot assume all parts remain serviceable just because the engine was still running before removal[cite: 1]. Wear across individual components can be uneven, so each part requires an individual evaluation[cite: 1].

During the overhaul, special attention was paid to the precise fitment of all crank-piston components[cite: 1]. New or reconditioned parts must operate together within strict factory tolerances[cite: 1]. Following this work, all parts were prepared for assembly according to proper engine-building procedures[cite: 1].

### Cylinder Head Repair and Verification

The Cummins QSB 4.5 cylinder head was thoroughly cleaned and evaluated for continued use[cite: 1]. Inspection covered the condition of valve seats, valve guides, valves, and overall seal integrity[cite: 1].

Depending on the level of wear, head reconditioning involves resurfacing (planing) as well as replacing valve guides and valves[cite: 1]. The goal is to achieve flawless sealing and proper working conditions for the valvetrain[cite: 1].

Once work was completed, the cylinder head was verified again[cite: 1]. This is crucial for an engine destined to operate under heavy load in a telehandler[cite: 1]. The JLG 1055 engine must respond smoothly both during light duty and when the operator demands maximum performance from the machine[cite: 1].

### Fuel System and Accessory Inspection

During the overhaul, we did not limit our work to internal engine block components[cite: 1]. The fuel system and external accessories working with the Cummins QSB 4.5 were also verified[cite: 1]. In a diesel engine, proper fuel system operation directly impacts combustion quality, power output, and overall running stability[cite: 1].

Fuel system components underwent thorough inspection[cite: 1]. If indicators suggested a need for closer examination during verification, injection components could be tested on a test bench[cite: 1]. This allows us to verify their true operational condition rather than assessing them purely by visual appearance[cite: 1].

The turbocharger was also checked[cite: 1]. We measured axial and radial play and evaluated its overall condition for continued operation[cite: 1]. Electrical and mechanical accessories were inspected as well to ensure seamless integration with the newly overhauled power unit[cite: 1].

### Professional Assembly of the Cummins QSB 4.5 Engine

Following verification and component preparation, we began reassembling the Cummins QSB 4.5 engine[cite: 1]. Rebuilding an engine after an overhaul requires adhering to a strict work sequence and meticulous accuracy at every connection[cite: 1]. Replacing worn parts is not enough—the entire engine must be assembled to guarantee smooth collaboration between all subassemblies[cite: 1].

During assembly, we focus closely on mating surface conditions, correct alignment, and proper torque values for all fasteners[cite: 1]. The crank-piston assembly must be built within exact dimensions and tolerances[cite: 1]. Properly sized main/rod bearings, pistons, rings, and other parts specified in the overhaul scope are systematically installed[cite: 1].

Concurrently, the cylinder head and valvetrain components are prepared[cite: 1]. Once the head is mated to the engine block, accessories, intake, exhaust, cooling, and lubrication components are installed[cite: 1]. Every joint must be inspected, as a subsequent leak in an oil, fuel, air, or coolant line could compromise operational safety[cite: 1].

For an engine returning to a telehandler, preparing it not just to start, but to perform under real work conditions is paramount[cite: 1]. Therefore, prior to delivering the unit for installation in the JLG 1055, we perform a comprehensive completeness check on the engine and all installation hardware[cite: 1].

After assembly, the Cummins QSB 4.5 was prepared for startup and testing on our **engine dynamometer**[cite: 1]. This represents one of the most vital stages of the entire overhaul process[cite: 1].

### Cummins QSB 4.5 Dyno Testing

Simply having an engine start after an overhaul does not mean the repair is complete[cite: 1]. That is why we place great emphasis on testing units on an engine dynamometer[cite: 1]. Dyno testing allows us to evaluate engine performance under load before it is ever reinstalled into a machine[cite: 1].

After initial startup, the reconditioned Cummins QSB 4.5 is not immediately subjected to maximum load[cite: 1]. An overhauled engine must first break in under controlled conditions[cite: 1]. For a minimum of 16 hours, it runs under a light load of approximately 20-30% of rated capacity[cite: 1]. This stage allows new components to settle smoothly while basic operating parameters are continuously monitored[cite: 1].

During dyno operation, we track unit performance, operating temperatures, oil pressure, and load responsiveness[cite: 1]. We also inspect for potential leaks or unusual symptoms[cite: 1]. The dynamometer provides the ability to conduct these tests in a controlled environment without needing to install the engine in the machine just to verify post-overhaul functionality[cite: 1].

Upon completing the initial trial period and confirming stable operation, load is gradually increased[cite: 1]. Further tests are conducted with the engine operating under higher loads repeatedly[cite: 1]. This verifies how the Cummins QSB 4.5 handles changing conditions and whether parameters remain nominal at full operating temperature[cite: 1].

Dyno testing also serves as an additional quality control step for the overhaul[cite: 1]. Should an issue arise during testing, we can address it immediately before dispatching the engine to the client and prior to mounting it in the JLG 1055[cite: 1]. This eliminates the risk of discovering an issue after installation that would require removing the engine a second time[cite: 1].

The capability to perform load testing is a cornerstone of our engine overhaul process[cite: 1]. A dyno verifies the unit under conditions far closer to actual field work than simply starting an engine on a static stand[cite: 1]. For engines powering construction equipment and telehandlers, this is especially critical given their variable and demanding load cycles[cite: 1].

Following successful completion of dyno tests, the Cummins QSB 4.5 engine was prepared for transport and reinstallation into the JLG 1055 telehandler[cite: 1].

### Installing the Overhauled Engine in the JLG 1055

After passing dyno testing, it was time to reinstall the Cummins QSB 4.5 into the JLG 1055 telehandler[cite: 1]. Engine installation is just as critical as the overhaul itself[cite: 1]. Even a perfectly rebuilt engine can experience operational issues if installed incorrectly or if its connections to the machine's systems are not thoroughly verified[cite: 1].

Our mechanics prepared the mounting bay in the engine compartment and proceeded to guide the unit into place[cite: 1]. A **crane provided by the client** was used for lifting and positioning[cite: 1]. The process was executed carefully to avoid damaging hoses, mounts, or other components located in the engine bay[cite: 1].

Once the engine was positioned correctly, it was secured to its mounts[cite: 1]. Next, wiring and plumbing systems were reconnected[cite: 1]. We paid close attention to the cooling system, lubrication system, air intake, exhaust, and electrical wiring[cite: 1]. Every connection must be precise, as even a minor intake leak can affect performance, and a coolant leak can lead to severe consequences during operation[cite: 1].

During installation, we also inspected hard piping and flexible hoses[cite: 1]. If lines or connections showed signs of wear, they were serviced or replaced accordingly[cite: 1]. This applied particularly to air intake hoses and cooling system lines[cite: 1]. Once all systems were connected, routing was double-checked to prevent chafing or contact with moving parts[cite: 1].

Prior to initial startup, pre-start procedures were carried out, including replacing relevant filters and checking fluid levels[cite: 1]. All connections made during installation were inspected again[cite: 1]. Only after completing these checks was it safe to start the engine[cite: 1].

Upon starting, the Cummins QSB 4.5 was initially run without load so mechanics could inspect its behavior with all systems reconnected[cite: 1]. Our team monitored operating parameters and inspected cooling, intake, exhaust, and lubrication connections for leaks[cite: 1].

We then proceeded to field testing the JLG 1055 under operational conditions[cite: 1]. The machine operator participated in these tests, as their experience helps assess machine responsiveness and engine behavior during typical work cycles[cite: 1]. We checked RPM response and engine performance under increasing load[cite: 1].

Testing was performed incrementally[cite: 1]. We first evaluated basic engine operation before moving to more demanding trials[cite: 1]. We verified that the engine handled load properly without unusual noises, vibrations, or leaks[cite: 1]. Additionally, all installation joints were re-checked for tight sealing[cite: 1].

Only after successful field tests was the installation deemed complete[cite: 1]. Once proper operation was confirmed and no leaks were detected, an installation report was completed[cite: 1].

### Post-Overhaul Engine Maintenance

The overhaul of a Cummins QSB 4.5 engine does not end the moment the JLG 1055 starts up[cite: 1]. Following a major repair, proper maintenance during the initial break-in period is crucial[cite: 1].

We recommend conducting the first service inspection at **50 operating hours (mth) after engine startup**[cite: 1]. This service is performed by our field technicians, who can travel directly to the customer site[cite: 1]. It goes beyond a simple filter change[cite: 1]. Technicians check the overall condition of accessories, engine running parameters, and connections between the engine and the machine[cite: 1].

After the initial 50 hours of operation, minor leaks that may have developed during normal work can be identified[cite: 1]. Catching these early allows for quick resolution and prevents major failures down the road[cite: 1].

Subsequent service inspections are recommended every 250 operating hours (mth), or at least once every 3 months[cite: 1]. Regular maintenance keeps track of engine health and enables prompt responses to changes in performance[cite: 1].

### Which Machines Use the Cummins QSB 4.5 Engine?

The Cummins QSB 4.5 is a common power unit in off-highway machinery[cite: 1]. Engines from this family can be found in wheel loaders, excavators, screeners, crushers, rollers, dumpers, and other heavy equipment[cite: 1]. However, specific engine configurations can vary depending on the equipment manufacturer, build version, and installed accessories[cite: 1].

Therefore, when ordering parts or planning an overhaul, you should not rely solely on the engine model name[cite: 1]. In practice, part numbers, data plate details, engine serial numbers, and machine configuration are essential[cite: 1]. This applies directly to the JLG 1055 powered by the Cummins QSB 4.5[cite: 1].

Based on engine data, we can define the required scope of work and select the correct parts[cite: 1]. For an overhaul, this minimizes the risk of using components that do not match the specific engine configuration[cite: 1].

### Construction Equipment Service and Diesel Engine Overhauls

The Cummins QSB 4.5 overhaul from the JLG 1055 telehandler demonstrates why a comprehensive approach to engine repair matters[cite: 1]. Diagnostics starting inside the machine clarify the repair strategy, while teardown and precision measurements in the workshop verify the true condition of components[cite: 1].

WIBAKO provides **construction machinery service**, engine removal and installation, and complete overhauls of power units used in off-highway equipment[cite: 1]. Our mobile service team can perform work directly at the customer's site, and removed engines can be transported to our headquarters in Kojszówka for detailed inspection and repair[cite: 1].

For Cummins engines, correctly identifying the specific engine build is critical[cite: 1]. The QSB 4.5 exists in various applications, which is why we analyze all available engine and machine data before commencing work[cite: 1].

A comprehensive overhaul gives clients more than just repaired parts; it provides proof of performance before the engine ever returns to the machine[cite: 1]. Load testing on our dynamometer validates the engine under load and provides an extra tier of quality assurance[cite: 1].

### Summary of the Cummins QSB 4.5 Overhaul in the JLG 1055

The JLG 1055 telehandler has been reunited with a fully reconditioned Cummins QSB 4.5 engine ready for work[cite: 1]. The overhaul was preceded by in-machine diagnostics, after which the engine was removed and transported to our facility in Kojszówka[cite: 1].

In our workshop, we tore down the engine and performed a thorough inspection[cite: 1]. We checked the crank-piston assembly, crankshaft, connecting rods, pistons, rings, liners, bearings, cylinder head, fuel system, and engine accessories[cite: 1]. Based on measurement results, necessary overhaul work was executed[cite: 1].

Following assembly, the unit was started and dyno tested[cite: 1]. It was first run under light load conditions and then progressively loaded to verify performance under heavy duty[cite: 1]. Only after passing these tests was the engine reinstalled into the JLG 1055[cite: 1].

Post-installation, we thoroughly checked all connections, mating systems, and seals for leaks[cite: 1]. Operational field tests were then conducted alongside the machine operator[cite: 1]. After confirming proper engine performance and no leaks, installation was finalized[cite: 1].

Following an overhaul, we recommend a first inspection after 50 operating hours[cite: 1]. Our service team can travel to the client site to inspect the engine and related machine components[cite: 1]. Subsequent inspections should occur every 250 operating hours or at least every 3 months[cite: 1].

If you require a **Cummins QSB 4.5 engine overhaul**, engine diagnostics, or JLG telehandler service, we can handle the entire process—from diagnostics and removal, through engine rebuilding and dyno testing, to final reinstallation into your machine[cite: 1].

### Related Materials and Information

Cummins Engine Overhauls

Construction Machinery Service

Cummins Engine Parts

Mobile Service for Construction Machinery

Engine Dynamometer - Engine Load Testing

### Contact Us

Need a Cummins QSB 4.5 engine overhaul or service for a JLG 1055 telehandler? Contact us—we offer comprehensive repairs, installation, and engine load testing on our dynamometer.

[+48 33 870 42 00](tel:+48338704200) [biuro@wibako.pl](mailto:biuro@wibako.pl) [Formularz](https://wibako.com/contact)

Published: 2026-09-03

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Source: https://wibako.com/about-us/news/774-repair-of-the-cummins-qsb-4-5-engine-in-the-jlg-1055-telehandler
Contact: +48338704200, biuro@wibako.pl