Volvo D12D Engine Overhaul in a Volvo A35D Articulated Hauler – Comprehensive Service with Engine Dynamometer Testing

The Volvo A35D articulated hauler belongs to a group of machines designed for intensive operation in mines, quarries, gravel pits, and during large-scale infrastructure projects. The design of the A35D model was engineered for long hours of heavy-duty operation, which is why it is powered by the 12-liter, six-cylinder Volvo D12D engine, providing excellent refinement and high torque essential for transporting heavy loads. This power unit was used in many Volvo CE machines and was built for long service life in harsh environments. The production of the A35D model with the D12D engine was aimed at adapting the machine to newer emission standards while maintaining peak operating parameters.

Our service center received a Volvo D12D engine from a hauler operating near Katowice. The operator reported a gradual loss of power, increased oil consumption, and noticeable smoking under load. Our mobile service team carried out on-site diagnostics, followed by the engine disassembly using a crane provided by the customer. The unit was then transported to our headquarters in Kojszówka, where a full inspection and a comprehensive overhaul began.

Initial Diagnostics of the Volvo D12D Engine

The first stage involved diagnostics carried out while the engine was still in the machine. Mechanicians measured compression pressure, evaluated the unit's operating parameters during warm-up, and analyzed the intake and fuel systems. The results indicated significant wear on the cylinders and components of the crank-piston system.

Additionally, an endoscopic inspection of the cylinder interiors was performed. Signs of wear on the sleeve surfaces and carbon deposits on the pistons were visible. The oil consumption analysis and engine operating parameters confirmed the necessity of a complete engine overhaul.

Engine Disassembly from the Volvo A35D Hauler

Disassembly was performed by our mobile service using a crane provided by the machine owner. Before removing the unit, the electrical installation, fuel lines, cooling system, charge air pipes, and exhaust system components were disconnected. All lines and wires were labeled to ensure that subsequent reassembly complies with the manufacturer's documentation.

After removing the engine, all open ports were protected against contamination. The condition of the engine mounts, clutch, drivetrain components, and wiring inside the engine bay was also thoroughly checked. This allowed us to plan the scope of additional work to be performed during the reassembly of the unit.

Workshop Engine Verification

Upon delivery of the engine to the workshop, a complete teardown began. Initial inspections immediately confirmed the assumptions from the on-site diagnostics. The cylinder liners showed significant wear, the piston rings had lost their sealing properties, and the piston surfaces bore signs of long-term operation.

A full crankshaft inspection was carried out, including measurements of main journals, crankshaft runout, oil gallery checks, and microcrack testing. Connecting rods, camshaft, cylinder head, turbocharger, injection pump, and electrical accessories were all verified. The cylinder head underwent a pressure test in a water bath, while the injection pump was sent to a specialized test bench.

Crank-Piston System Regeneration

The scope of the overhaul included replacing the cylinder liners, new pistons, piston rings, main bearings, and connecting rod bearings. The crankshaft was ground according to the measurement results. All components were selected in accordance with the requirements of the Volvo D12D engine manufacturer.

The connecting rods were checked for straightness, weight, and bolt condition. After completing the measurements, they were prepared for reassembly. Particular attention was paid to correct assembly clearances and maintaining the parameters specified by the manufacturer.

Cylinder Head and Fuel System Regeneration

The cylinder head underwent a full refurbishment, including surface resurfacing, replacement of valve guides, valves, and stem seals. After completing the work, a re-test for tightness and geometry control was performed.

The fuel system was subject to precise control. The injection pump was tested on a test bench, while the injectors underwent adjustment and spray pattern testing. This made it possible to achieve uniform operation across all cylinders after completing the overhaul.

Engine Accessories Regeneration

The turbocharger was verified by measuring the radial and axial play of the rotor. The alternator, starter, water pump, intake pipes, and electrical system components were also inspected. All seals were replaced with new ones, and wires or hoses requiring replacement were substituted with brand-new components.

Professional Engine Assembly

Following the completion of all work, the engine was assembled in accordance with Volvo's service documentation. Every component was tightened to the appropriate torque specifications. Before closing the unit, a clearance check was performed, and the crankshaft was manually rotated through two full working revolutions.

After successful workshop tests, the engine was transported back to the customer. Our mobile service utilized the crane provided by the machine owner again and mounted the unit into the hauler's frame. The cooling system, fuel lines, air intake, electrical installation, hydraulic lines, and exhaust system were reconnected. All filters and operating fluids were replaced.

After the initial startup, the fuel system was bled, oil pressure was checked, and all connections were inspected for leaks. Next, test drives with varying loads were carried out together with the operator. Operating temperatures, oil pressure, load response, and the proper cooperation of the engine with the hauler's drivetrain were checked. An assembly protocol was drawn up upon completion of the tests.

Dynamometer Engine Testing

One of the most crucial stages of the whole process was the test on our engine dynamometer (dyno). Before sending the engine to the customer, every overhauled unit undergoes a multi-hour test run. In the first phase, the Volvo D12D engine ran for over 16 hours at a load of approximately 20-30% of its nominal value. This allows the cooperating elements of the crank-piston system to bed in correctly and enables monitoring of all operating parameters.

During the tests, parameters such as oil pressure, coolant temperature, oil temperature, boost pressure, fuel consumption, and stability at various engine speeds are closely monitored. Thanks to specialized equipment, it is possible to detect even minor deviations that would be difficult to notice under field conditions.

After the break-in period, the engine is repeatedly loaded to values close to nominal. We check the fuel system response, turbocharger behavior, temperature stability, and the tightness of all systems. The dynamometer also allows us to verify the achieved power and torque, assessing the correctness of the overhaul.

As a result, the customer receives a unit tested even before installation in the machine. This is one of the greatest advantages of our service, as most workshops perform only a short engine startup. We are able to verify its behavior under conditions corresponding to real operation, which significantly reduces the risk of issues after mounting the unit in the hauler.

Post-Overhaul Engine Maintenance

Following the repair, the customer received recommendations for future operation. The first service check is performed after 50 operating hours by our mobile service. It includes changing filters, checking all connections for leaks, evaluating accessory operation, and verifying engine parameters. Subsequent inspections are carried out every 250 operating hours, but not less than once every three months.

Machines Equipped with the Volvo D12D Engine

The Volvo D12D engine was used not only in Volvo A35D articulated haulers but also in A40D models and many other heavy construction machines by Volvo. This unit is valued for its high torque, durability, and the potential for long-term operation after a properly executed overhaul.

Summary

The comprehensive overhaul of the Volvo D12D engine included full diagnostics, disassembly, detailed verification, component regeneration, engine dynamometer testing, and professional installation in the Volvo A35D articulated hauler. Thanks to this comprehensive approach, the customer received a power unit prepared for many more years of operation.

If you own a Volvo A35D articulated hauler or another machine equipped with a Volvo D12D engine and notice signs of engine wear, we perform comprehensive diesel engine services, major overhauls, engine rebuilding, as well as mobile disassembly and assembly at the customer's site. Every engine undergoes testing on a professional engine dynamometer after the overhaul.

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