A 2007 Komatsu PC350LC crawler excavator arrived at our yard – about 35 tonnes, standard boom, around 25,000 operating hours on the clock. The engine had failed and rebuilding it no longer made sense. The owner opted for a rebuilt Cummins QSC8.3 that we had available from stock. It looks like a simple swap – in practice it required a complete conversion.
Removing the old engine
After disconnecting the battery isolator and batteries, we removed the fan, the exhaust and the air hoses. The hydraulic pump was separated from the flywheel housing and supported so it would not hang on the shaft. Then we undid the engine mounts and lifted the engine out. The advantage of a large excavator: plenty of room to work. We protected the engine bay and gave it an initial clean.
Converting the Cummins QSC8.3 “one-to-one”
The QSC8.3 is a development of the proven 6CT8.3 – with a common rail system and a 24-valve cylinder head. The fuel system was the same as on the customer's engine, but there were many differences, and we always try to convert an engine so it fits the machine like the original:
- turbocharger and exhaust manifold – the turbo was oriented the other way; the customer's turbocharger was sent out for reconditioning,
- oil sump – different from the machine's,
- flywheel housing and flywheel – transferred from the customer's engine, coupling checked,
- valve cover with oil filler – the customer's filler is at the rear, ours at the front,
- oil dipstick – slightly different length,
- wiring harness and ECU – the ECU removed before washing, the harness checked electrically so no errors would appear after installation.
Dyno
The converted engine went onto the dyno. Once warmed up to about 85°C, the oil pressure was 3.5 bar – excellent. The engine ran until the end of the day under increasing load, up to maximum, while we checked for leaks. The rule is simple: if something is going to fail, let it fail on the dyno, not in the machine.
Installation and start-up
We first seated the rear of the engine on its mounts and supported the pump on a forklift to line up the shaft. After bolting on the ancillaries and exhaust, the engine started with no errors. We also replaced the full set of filters (air, and fuel filters mounted off the engine) and repaired several badly leaking hydraulic hoses. The excavator drives and works.
Takeaways
- With high hours and a serious failure, swapping in a rebuilt engine can be faster and cheaper than an overhaul.
- The “same” engine model does not mean identical ancillaries – a 1:1 conversion avoids problems during installation and operation.
- A dyno test before installation gives confidence that the engine is sound.
See our combustion engine overhauls.
Watch the repair video: Komatsu PC350LC With a Dead Engine. End of the Machine or a Major Repair?
