| Attribute | Specification |
|---|---|
| Production Years | 1988–1991 |
| Engine Type | 647cc Liquid-cooled 52° V-twin |
| Oil Requirement | SAE 10W-40 API SE/SF/SG (JASO MA/MA2) (2.3 L) |
| Tires (F/R) | 110/80-17 57H / 150/70-17 69H |
| Tire Pressure (F/R) | 2.25 bar (33 psi) / 2.50 bar (36 psi) |
| Battery | YTX9-BS |
| Spark Plug | NGK DPR8EA-9 or Denso X24EPR-U9 |
The Honda NT 650 Hawk GT, designated internally as the RC31, holds a unique place in motorcycling history as the first production Honda to feature the Pro-Arm single-sided swingarm (a technology licensed from ELF) paired with a massive aluminum twin-spar frame. Predating the Ducati Monster by half a decade, the Hawk GT pioneered the ‘naked bike’ performance aesthetic, combining sportbike handling with a narrow, minimalist profile.
Technical Engineering Review
At the heart of the RC31 is a 647cc, liquid-cooled, 52-degree V-twin engine. While the power figures were modest by late-80s standards, the delivery was exceptionally linear. The engine features a three-valve-per-cylinder head design (two intake, one exhaust) and dual spark plugs per cylinder, ensuring efficient combustion and a broad torque curve.
The chassis is where the RC31 truly shines. The aluminum frame was incredibly stiff for its era, and the Pro-Arm swingarm wasn’t just a visual gimmick; it allowed for rapid rear-wheel changes and provided a distinct center of gravity that made the Hawk one of the most flickable motorcycles ever produced. Its cult status today is driven by its reputation as a ‘giant killer’ on tight, technical tracks.
Maintenance Guide & Service Intervals
Lubrication System
To maintain the longevity of the V-twin, use a high-quality SAE 10W-40 oil meeting JASO MA or MA2 standards. The total capacity for an oil change with filter is 2.3 Liters. Given the age of these machines, regular oil analysis is recommended to check for bearing wear.
Tires and Handling
The RC31 relies heavily on its geometry for its legendary handling. Ensure tires are maintained at 2.25 bar (33 psi) in the front and 2.50 bar (36 psi) in the rear. Modern radial tires in the 110/80-17 and 150/70-17 sizes can significantly modernize the grip levels compared to original 1980s bias-ply options.
Electrical and Ignition
The Hawk GT uses a YTX9-BS battery. If the bike experiences sluggish starting, check the regulator/rectifier, as these were common failure points on Hondas of this era. For ignition, utilize NGK DPR8EA-9 plugs, gapped to 0.8–0.9mm. The dual-plug setup requires four plugs in total.
Frequently Asked Questions (FAQ)
What makes the RC31 frame special?
It was one of the first naked bikes to use a large-section aluminum twin-spar frame, typically reserved for flagship sportbikes like the RC30.
Is the Honda Hawk GT a good beginner bike?
While it is approachable due to its low seat height and predictable power, its status as a collector’s item and the scarcity of certain body parts make it better suited for enthusiasts and collectors today.
How often should I check the valves?
Standard service intervals suggest checking the valve clearances every 12,000 miles (approx. 19,000 km) to ensure the three-valve heads are operating optimally.