Honda GX630 20 HP V-Twin Gas Engine - 688cc OHV, Electric Start, Muffler Included

The Honda GX630 is a 688cc OHV V-twin, the engine that drives the larger end of the engine-driven compressor range where a single-cylinder GX390 runs out of torque. Twin cylinders give it a smoother pull and a far better part-throttle manner than a big single, which matters on a compressor that idles down between cycles all day.

This is the RQAF1 configuration: 12 volt electric start with a 17 amp charging system, fuel pump, full-pressure oil filter, oil cooler, and a throttle panel with key switch. It is supplied here with the muffler, which the bare QAF engine does not include.

Key specifications

• Displacement: 688 cc (42 cu in), OHV V-twin, air cooled
• Net power: 20.8 HP (15.5 kW) at 3,600 RPM
• Net torque: 35.6 lb-ft (48.3 Nm) at 2,500 RPM
• Shaft: 1 in diameter straight keyed horizontal, 1/4 in keyway, drilled and tapped 3/8-24. Published usable length is 2-7/8 in
• Start: 12 volt electric, 17 amp charging
• Lubrication: full pressure with oil filter and oil cooler
• Oil capacity: 2.1 US quarts
• Dry weight: approximately 97 lb for the engine
• Fuel tank: none. This is a bare engine with a fuel pump, fed from a remote tank
• Muffler: included

No fuel tank, and why that is normal

The GX630 in this configuration ships without a fuel tank. On a compressor, a generator or a truck-mounted unit that is what you want, because the tank belongs on the frame where it can be filled and strapped properly, not perched on the engine. A fuel pump is fitted as standard so the tank can sit below the carburettor. We can supply the Honda 5 gallon fuel tank and carbon canister kit and its mounting bracket set separately. Ask us and we will quote the set with the engine.

About the 20 HP figure

Honda's published net rating for this engine is 20.8 HP at 3,600 RPM, so the familiar 20 HP label is a round-down rather than a gross figure that the engine cannot reach. That is a different situation from the single-cylinder GX engines, where the well-known horsepower numbers are legacy gross ratings.

Repowering a compressor

Check the shaft first. This is the 1 in Q-type keyed shaft, and the usable length is reported between 2-3/4 in and 2.9 in depending on the source, so measure your existing sheave before you bore or buy one. Then check the idler and unloader arrangement, because a gas compressor has to start unloaded and that assembly is engine-specific. We stock the matching engine idler for the GX630 and the adapter plates that go with it. Tell us the compressor and we will confirm the set.

Typical applications

Large service truck and trailer air compressors, two-stage portable compressors in the 15 to 25 CFM class, commercial pressure washers, generators, large pumps and heavy construction equipment.

The Honda GX630 is a 688cc OHV V-twin rated 20.8 HP net, with 12 volt electric start, pressure lubrication with oil cooler, a 1 in keyed shaft and the muffler included. 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.