Honda GX390 13 HP Gas Engine - 389cc OHV, 1 in Keyed Shaft, Electric or Recoil Start

The Honda GX390 is the engine most belt-drive gas air compressors in the 8 to 13 HP class are built around, and the one most of them are repowered with. A 389cc single-cylinder OHV commercial engine with a cast iron cylinder sleeve, a ball-bearing supported crankshaft and a reputation for starting on the second pull after a winter in an unheated shop.

This listing covers both starting configurations on the same engine. The electric-start version carries a 12 volt starter and charging system with recoil as backup, which is what a truck-mounted or trailer compressor wants. The recoil-only version is the same engine without the starter, battery or charging circuit, and costs substantially less if your machine has no 12 volt system to begin with.

Key specifications

• Displacement: 389 cc (24 cu in), single cylinder OHV, air cooled
• Bore x stroke: 88 x 64 mm
• Net power: 11.7 HP (8.7 kW) at 3,600 RPM, SAE J1349 net
• Net torque: 19.5 lb-ft (26.5 Nm) at 2,500 RPM
• Shaft: 1 in diameter x 3-31/64 in, straight keyed horizontal, tapped 3/8-24 UNF, 1/4 in keyway
• Fuel tank: approximately 1.6 US gallons
• Oil capacity: 1.16 US quarts
• Dry weight: approximately 69 lb recoil, approximately 75 lb with the electric starter fitted

About the 13 HP figure

The GX390 is universally known as a 13 HP engine and that is how the compressor industry specifies it, so that is how it is listed here. It is worth knowing that 13 HP is the legacy gross rating. Honda's current published figure for this engine is 11.7 HP net under SAE J1349, measured with the production muffler and air cleaner fitted. Nothing about the engine changed, only the way the rating is quoted. If you are replacing a 13 HP GX390 on an existing machine, this is the same engine.

Which start do you need

• 12V electric with recoil (M5035): choose this to replace an electric-start engine, or on any unit with a battery, a key switch and a charging circuit. The recoil stays fitted as a backup.
• Recoil only (M5039): choose this where there is no 12 volt system on the machine. It will not accept the starter as a bolt-on afterthought, so decide before you order.

Repowering a compressor

Check three things before you buy. First, shaft diameter and length: this is the 1 in Q-type shaft, which is what most 8 to 13 HP compressor sheaves are bored for. Second, your idler and unloader arrangement, because a gas compressor needs to start unloaded and the idler assembly is engine-specific. Third, the mounting pattern and belt centre distance. We stock the matching engine idler assembly for the GX390 and the adapter plates and motor rails that go with it, so tell us the compressor and we will make sure the whole set goes together.

Typical applications

Service truck and trailer air compressors, portable wheelbarrow and skid compressors, pressure washers, generators, pumps, plate compactors and general construction equipment in the 10 to 13 HP class.

The Honda GX390 is a 389cc OHV commercial gas engine with a 1 in keyed horizontal shaft, available here in 12 volt electric start with recoil or recoil only. Tell the Warthog Air Compressor Store team what machine it is going on and we will confirm the shaft, the idler and the mounting before you order.