Overview#
The Atlas Copco QAS 125 delivers 100 kW of prime power from a John Deere 4045 HFG04 four-cylinder engine — the first model in the QAS lineup to use a John Deere powerplant instead of Isuzu. The 166-gallon integral tank provides extended runtime, and the unit features DOC and SCR aftertreatment for Tier 4 Final compliance.
The Leroy Somer LSA 44.3 S5 alternator maintains ±0.25% voltage regulation. At 73 dBA, the QAS 125 is louder than the smaller Isuzu-powered models but remains competitive in its class. The unit features 500-hour service intervals and long-run filters for reduced maintenance.
John Deere 4045 platform and extended service intervals#
The transition from Isuzu to John Deere at the 100 kW level brings several advantages. The John Deere 4045 HFG04 is a 4.5-liter four-cylinder diesel used extensively across the generator industry, which means a well-established parts supply chain and broad dealer service network. Oil change intervals extend to 500 hours — double the 250-hour intervals on the smaller Isuzu-powered QAS models — reducing ongoing maintenance costs for high-utilization units.
The Leroy Somer LSA 44.3 S5 alternator steps up from the 42.3 series used in the QAS 25-70, delivering the higher output capacity needed for 100 kW applications while maintaining the same ±0.25% voltage regulation and AREP excitation system that defines the QAS lineup.
Our service experience#
The QAS 125 marks the transition point in the Atlas Copco QAS lineup from Isuzu to John Deere power. For service professionals, this is significant — the John Deere 4045 has a broader aftermarket parts ecosystem and a more accessible dealer network than the Isuzu engines in the smaller models. This partially offsets Atlas Copco's well-documented after-sale service shortcomings.
That said, Atlas Copco's own service network remains the brand's biggest weakness. Owners report unreturned service calls, travel charges exceeding $311/hour, and multi-week waits for factory-specific parts (enclosure components, control panels, and Atlas Copco-branded accessories). For QAS 125 owners in Northern California, OnPoint provides local maintenance and repair — we are familiar with both the Isuzu and John Deere powerplants across the full QAS lineup.
