Repair and Testing of the Mercedes OM906 Engine in the Liebherr LTM1050 Crane

Introduction

The Liebherr LTM1050 mobile crane is a compact, mobile all-terrain crane valued by crane companies for its combination of high load capacity and mobility. In this case, the machine was powered by a Mercedes OM906 engine, which is an inline, six-cylinder diesel unit known for its high work culture and durability in off-highway applications. The WIBAKO team was called in for full service: diagnostics, disassembly, general overhaul, testing on the dynamometer, and reassembly with commissioning and post-execution inspection.

The impetus for the order was a noticeable loss of power under load and unstable oil pressure during the crane's operation in off-road mode. Additionally, the operator noted metallic knocking during rapid changes in RPM. Initially, we suspected wear of the crankshaft bearings and connecting rods, as well as possible localized damage to the crank-piston system resulting from operation in harsh conditions.

In the material below, we present the full course of service work, verification and repair standards at WIBAKO, and unique benefits from using our engine dynamometer for load testing before installation in the machine.

Preliminary diagnostics in the machine

We started by measuring the actual oil pressure and recording its changes as a function of RPM. Additionally, we performed a basic oil condition analysis by disassembling the filter to check for the presence of metal shavings. To assess the condition of the cylinder sections, we conducted a compression test on the warmed-up engine, followed by a brief endoscopy through the injector ports. Based on this, we confirmed that the problem was not limited to the accessories but was mechanical in nature.

The target diagnostics before the decision to disassemble included checking the operating parameters of the turbocharger, inspecting the intake and intercooler for leaks, and conducting a smoke test. The values confirmed the hypothesis of bearing wear and possible localized seizure on one of the crankshaft journals.

Engine disassembly

The disassembly took place in the Małopolskie Voivodeship, near Kraków. Our mobile service arrived on site and prepared the machine for the removal of the power unit. According to WIBAKO standards, engine disassembly is always performed using a crane provided by the client, which reduces downtime and ensures safety. We disassembled the externally accessible accessories, disconnected the fuel lines, cooling system, air intake, and exhaust, as well as electrical harnesses and control elements. All ports and ends of the systems were sealed with caps to prevent contamination from entering the lubrication and cooling systems.

After unscrewing the engine bed, clutch, and support mounts, the unit was lifted out of the crane frame and prepared for transport. The packed and properly secured OM906 was transported to our headquarters in Kojszówka, where we perform disassembly, cleaning, verification, and repair processes in workshop conditions.

Verification of components in the workshop

After preliminary chemical cleaning, we disassembled the engine into parts and proceeded with verification. The crankshaft was visually inspected for discoloration and microcracks, we checked the crankshaft runout and the diameters of the journals against dimensional tolerances. The connecting rods were checked for twisting and longitudinal bending, and we measured their mass to exclude differences exceeding acceptable deviations. The cylinder head was tested for tightness in a water bath, and we checked the valve seats and guides. The camshaft was measured at the journals and lobes, assessing the profile and wear of the raceways.

The verification of the boost system included checking the axial and radial clearances of the turbocharger and analyzing the axial alignment of the rotor. The fuel system was tested on a test bench, checking the flow rates and atomization of the injectors, as well as the operating parameters of the injection pump. The verification results confirmed significant wear of the main and connecting rod bearings and the necessity for crankshaft regeneration along with the selection of new bearings of the appropriate oversize.

Regeneration and repair

Crank-piston system

The crankshaft underwent controlled grinding, along with cleaning and blowing out the oil channels. We replaced all main and connecting rod bearings with OEM quality parts, selected for the new size. The pistons, rings, and cylinder liners were assessed for compatibility after the crankshaft grinding. We used a complete set of new rings and a repair kit for the liners to restore factory sealing parameters and minimize blow-by into the crankcase.

Engine head

We performed surface planning, replaced guides, valves, and stem seals. After the operations, the seats were lapped, and the entire assembly underwent a final leak test. This resulted in proper compression and smooth operation at idle.

Fuel system and accessories

The injectors and injection pump received new repair kits and calibration after testing on the test bench. Additionally, we serviced the turbocharger, replacing the bearings and sealing elements, while the starter and alternator underwent inspection along with load tests.

Professional engine assembly

The assembly was conducted according to the specifications for torque and tightening angles for the OM906. We paid special attention to the cleanliness of the oil system, preparing the engine for the first start-up on the stand. We do not use the term regeneration of the timing system as a whole - the camshaft and individual elements of valve guidance and control can be regenerated, which was done according to the wear assessment.

Testing on the engine dynamometer

One of WIBAKO's greatest assets is its own engine dynamometer for off-highway units. It allows simulating real working conditions of the crane and checking engine parameters even before installation in the machine. This reduces the risk of surprises after installation, and the client gains assurance that the repaired unit achieves the expected power and torque values, responds correctly to loads, and maintains stable oil pressure and operating temperature.

The testing procedure consists of two phases. First, starting and running in with light load, usually 20-30 percent of nominal, for a minimum of 16 hours. During this time, we monitor operating parameters, including oil pressure, coolant temperature, exhaust temperatures, and fuel dose corrections. We analyze any irregularities immediately to eliminate them while still on the stand. The second phase involves full load tests in several cycles, with control of performance stability and repeatability of power at various set RPMs. Additionally, we perform a series of tests on the response to rapid application and removal of load, simulating the crane's operation during lifting and placing loads.

After successfully completing the tests, we prepare a protocol with the results, which includes a summary of performance, compression parameters, smoke emission test results, and recommendations for the initial operating period after installation. Such comprehensive testing on the dynamometer allows us to provide guarantees and shortens the crane's commissioning time for the client, as the unit arrives already tested, run-in, and ready for work.

Engine installation in the Liebherr LTM1050

The installation was again carried out near Kraków, with our mobile service arriving on site. After delivering the tested OM906, we prepared the engine compartment: we checked and cleaned the mounting bases, verified the condition of the engine mounts and clutch elements. Before lowering the unit into the crane frame, we replaced the complete set of filters and fresh oil, flushed the heat exchanger and cooling lines, and inspected the fuel tank for contaminants and water.

The process of introducing the engine into the compartment using the client's crane was assisted by two mechanics and an electrician. After positioning it on the supports and preliminarily tightening the bolts, we connected all lines: oil, fuel, return, and air intake with the intercooler. We ensured new clamps and gaskets at the connections, and we replaced the vacuum and vent lines with new sections. We paid special attention to the tightness of the intake system - it largely determines proper boosting and exhaust temperatures during the crane's heavy work.

After connecting the electrical harnesses, we conducted an integrity test of the installation: checking the resistance of grounds, continuity of signal wires from sensors, testing the alternator and starter under load. We then performed the start-up and multi-stage bleeding of the fuel system. The engine was warmed up to operating temperature, and we checked for any micro-leaks at all connections. In consultation with the crane operator, we conducted functional tests: operation at idle and elevated RPMs, simulating the working movements of the tower with a light load, and rapid changes in load to replicate real working conditions of the LTM1050.

After positive tests, we completed the post-execution documentation and signed the installation protocol. The machine returned to regular operation the same day, with guidelines for the first inspection.

Engine maintenance after repair

WIBAKO provides full service support after the unit's rebuild. We recommend the first filter change and inspection of all connections after 50 hours of operation from start-up in the machine. We plan periodic inspections every 250 hours, no less than once every 3 months. This allows us to maintain stable operating parameters, and any minor leaks or deviations are detected before they lead to downtime.

In which machines do we find the Mercedes OM906

The Mercedes OM906 engine is found not only in mobile cranes such as the Liebherr LTM1050 but also in many vehicles and special machines: municipal vehicles, fire trucks, selected loaders, equipment carriers, and construction machines of medium tonnage. Its popularity stems from a good compromise between durability and economy and the wide availability of parts.

Summary

Comprehensive service including diagnostics, disassembly, repair, testing on the dynamometer, and professional assembly restored the full functionality of the Liebherr LTM1050 crane. Thanks to our own dynamometer, WIBAKO was able to confirm the performance of the Mercedes OM906 engine even before installation, which shortened the commissioning time and minimized the risk of corrections. The client received a guarantee, documentation of results, and a maintenance schedule, and the machine returned to work with full power and stable oil pressure. We remind you of the inspection after 50 hours - our mobile service will arrive on site and perform a full check.