Repair of the Cummins QSB6.7 Engine in the Terex TL310 Loader

Engine Overhaul of Cummins QSB6.7 Stage IIIA in Terex TL310 Wheel Loader

The Terex TL310 wheel loader is one of the more popular machines used in construction, recycling plants, and aggregate management. Its compact design, high maneuverability, and efficiency make it widely used in intensive working conditions. In this article, we describe a comprehensive repair of the Cummins QSB6.7 Stage IIIA engine, which was carried out by the WIBAKO team at our headquarters in Kojszówka. The service was commissioned by a client from the Lesser Poland Voivodeship, and the disassembly of the power unit took place near the city of Krakow, with full support from our mobile service.

Introduction – Characteristics of the Terex TL310 Loader and Cummins QSB6.7 Stage IIIA Engine

The Terex TL310 wheel loader is a machine with an operating weight close to 18 tons and a bucket capacity of up to 3.3 m³. This machine is designed to work in harsh conditions where reliability and high breakout force are required. The manufacturer – Terex – has been specializing in off-highway equipment for years, and the TL310 model is an example of solid Western engineering.

The loader is equipped with a Cummins QSB6.7 Stage IIIA power unit – one of the most proven and popular engines installed in many construction machines. This engine features a power output of approximately 168–190 kW (depending on the configuration), Common Rail injection, and a variable geometry turbocharger in some variants. Its high operational culture and long lifespan mean that with proper maintenance, it can operate for many years. However, in this case, serious operational problems arose.

Cause of the Report – Preliminary Diagnostics

The client reported a problem with the engine's operation, describing: difficulties with starting, significantly reduced torque, and characteristic "popping" in the exhaust system. Additionally, there was noticeable intense white smoke, suggesting a problem with the combustion chamber's tightness or burnt valves. Upon the arrival of our mobile service, we performed basic diagnostics, including a compression test and analysis of the engine's operation at idle. The results showed very low compression in two cylinders, which clearly indicated damage and burning of the valves.

To unequivocally confirm the diagnosis, we conducted a cylinder leak test and an endoscopic examination. The camera introduced into the combustion chamber revealed clear material loss on the valves and overheating in the valve seats. The engine was not suitable for further operation, and a complete disassembly and transport of the unit to our workshop in Kojszówka was necessary.

Disassembly of the Engine in the Terex TL310 Loader

The disassembly was carried out at the machine's work site – at the aggregate yard near Krakow. The client provided a crane as per the guidelines, and our mobile service took care of preparing the engine for disassembly. The fuel, electrical, and cooling systems were disconnected, and the equipment was disassembled, including the aluminum intake pipes, which were secured against damage. The mounting brackets were unscrewed from the machine's frame, after which the engine was lifted and placed in our transport frame. It was then transported to Kojszówka, where the proper verification process began.

Verification of the Engine in the Workshop – Confirmation of Valve Damage

In the workshop, we conducted a complete disassembly of the Cummins QSB6.7 unit. Each component was cleaned and labeled. The cylinder head underwent a pressure test in a heated water bath, and its result unequivocally confirmed leaks in two valve seats and damage to two exhaust valves. Additionally, we noted increased wear on the guides and moderate wear on the cylinder liners.

The crankshaft underwent full measurement of the journals and inspection for cracks and play. The crankshaft was suitable for regeneration through grinding. The connecting rods underwent a twist and bend test – all met the standards, except for one that required replacement. The injectors were placed on the test bench, where they showed too large differences in dosing, so they were sent for regeneration at an external facility.

Regeneration of the Cummins QSB6.7 Stage IIIA Engine

Crankshaft-Piston System

As part of the rebuild, we performed: honing of the cylinder liners, replacement of the rings, installation of new main and connecting rod bearings, regeneration of the crankshaft, and replacement of one connecting rod. All components were measured and matched according to Cummins specifications.

Engine Head

The regeneration of the head included machining, replacement of all valve guides, installation of new valves, and lapping of the seats. After the work was completed, the head was rechecked with a pressure test.

Fuel System

The injectors were regenerated, and the high-pressure pump underwent testing and calibration on the test bench. The fuel system was thoroughly flushed to avoid the risk of re-contamination.

Accessories

The turbocharger was regenerated – axial and radial play were checked. The starter and alternator underwent servicing and brush replacement. All components were prepared for reassembly.

Professional Engine Assembly

The assembly process is one of the most important stages. Our team assembled the engine with full control of the tightening torques, according to Cummins documentation. All gaskets and O-rings were replaced. A new air piping system, cooling hoses, and fuel lines were assembled. Special attention was paid to the tightness of the intake system, as even the smallest leak could cause problems with the turbocharger's operation.

After assembling the unit, a leak test of the lubrication and cooling systems was performed. Only after positive results was the engine prepared for operation on the test bench.

Engine Test on the Test Bench – 16-Hour Load Tests

The engine test bench is one of WIBAKO's most important assets. Thanks to it, we have the opportunity to start the engine before installation in the machine, which minimizes the risk of malfunctions after installation. In the case of the Cummins QSB6.7, we conducted a 16-hour preliminary test under a load of 20–30 percent and multiple full loads. We analyzed temperatures, oil pressure, operational culture, boost parameters, and RPM stability.

The engine after regeneration operated flawlessly, achieving factory parameters. All readings were stable, and the exhaust emissions were within the norms for the Stage IIIA unit. After the tests were completed, a full report from the test bench was prepared and provided to the client.

Engine Installation in the Terex TL310 Loader

Our mobile service once again visited the client, where the engine was positioned in the compartment using a crane. We performed the installation according to the standards: bolting the mounts, connecting the fuel, electrical, intake, and cooling systems. We replaced all filters and filled the system with operational fluids.

After completing the installation, we conducted a series of tests with the operator. The loader was checked for leaks, proper acceleration, RPM stability, and operation under load. After positive tests, an installation protocol was signed.

Machines Featuring the Cummins QSB6.7 Engine

This engine is installed in, among others: loaders, tracked excavators, wheeled excavators, agricultural machines, lifts, technological dumpers, and many other off-highway machines.

Summary – Benefits for the Client

Thanks to the comprehensive regeneration and tests on the engine test bench, the client received a unit with factory parameters, ready to operate for thousands of additional operating hours. Our mobile service took care of the complete servicing of the machine in the field, and the regeneration carried out in Kojszówka ensures the highest quality and safety of operation. We remind you that the first inspection should be performed after 50 operating hours – our service will carry it out on-site at the client's location.

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