| Specification | Value |
|---|---|
| Model Designation | RC05 (Custom) |
| Production Years | 1980–1981 |
| Engine Type | 627cc SOHC Inline-4 |
| Oil Type | SAE 10W-40 (3.0 L) |
| Battery | YB12A-A (12V) |
| Tire Size (Front) | 3.50-19 57H |
| Tire Size (Rear) | 130/90-16 67H |
Historical Engineering Highlight: The Honda CB 650 C (RC05) represents a pivotal moment in Honda’s engineering timeline. It was the final significant iteration of the Single Overhead Cam (SOHC) inline-four engine architecture that began with the legendary CB750 in 1969. Unlike its predecessors, the RC05 featured a unique ‘leading-axle’ front fork design and a four-into-four exhaust system that sought to blend the performance of a middleweight sportbike with the burgeoning ‘Custom’ cruiser aesthetic of the early 1980s.
Technical Review: The RC05 Philosophy
At the heart of the RC05 is a 627cc engine that was essentially a bored-out and heavily revised version of the CB550 unit. By 1980, Honda engineers had pushed the SOHC design to its absolute limit to compete with the emerging DOHC (Double Overhead Cam) offerings from Kawasaki and Suzuki. The result was a surprisingly punchy engine that delivered approximately 63 horsepower, characterized by a smooth power delivery and the classic Honda reliability.
The chassis of the ‘Custom’ variant (RC05) focused on a relaxed geometry. The 16-inch rear wheel and 19-inch front provided that signature ‘chopper-lite’ stance, while the air-assisted front forks allowed for fine-tuning the suspension to handle the extra weight of the quad-pipe exhaust system.
Maintenance Guide & Vital Statistics
Lubrication System
For optimal engine longevity and clutch performance (the RC05 utilizes a wet multi-plate clutch), use 3.0 Liters of SAE 10W-40. It is critical to use oils meeting API SE or SF standards; modern energy-conserving oils should be avoided as they may cause clutch slippage in these vintage transmissions.
Ignition & Electrical
The RC05 utilizes a transistorized ignition system, which was a significant upgrade over the points systems of the 70s. For peak combustion efficiency, the NGK D8EA spark plugs must be maintained with a gap of 0.6–0.7 mm. The electrical system is supported by a YB12A-A lead-acid battery; given the age of these machines, ensuring clean ground connections is the most common fix for charging issues.
Tires and Chassis Pressure
The RC05’s handling is highly sensitive to tire pressure. The factory-recommended settings are:
- Front (3.50-19 57H): 2.0 bar (28 psi)
- Rear (130/90-16 67H): 2.25 bar (32 psi) for solo riding, increasing to 2.8 bar (40 psi) for pillion or high-load touring.
Editor’s Verdict
The Honda CB 650 C – RC05 is a bridge between eras. It offers the mechanical soul of the 1970s with the improved metallurgy and electronics of the 1980s. For the collector or the vintage enthusiast, it remains one of the most accessible and maintainable ‘Custom’ fours ever produced by the Hamamatsu factory.