Smiths RSM3003/12 Tachometer – Norton Commando S & Fastback, Black Face 4:1 (1968–1970)

Smiths RSM3003/12 tachometer Norton Commando S and Fastback — genuine original Smiths magnetic instrument as originally fitted to Norton Commando S and Fastback models from 1968 to approximately 1970. Black face, chrome bezel, 4:1 ratio, freshly serviced and tested — ready to fit.

The Norton Commando was introduced in 1968, and the earliest production bikes — the Commando S scrambler/sporting variant and the Fastback — used this distinctive black-face Smiths magnetic tachometer. The instrument reads to 9,000 RPM. The 4:1 ratio means the tachometer cable input spins at one quarter of the gearbox output speed. The tach drive is taken from the camshaft (which itself runs at half crankshaft speed), so the Smiths BG1508/06 2:1 reversing drive gearbox in the timing cover provides the correct final 4:1 reduction to drive this instrument accurately.

Smiths magnetic tachometers use a rotating magnet to drive the needle via an eddy current drag cup — the same operating principle as an analogue car speedometer. This design is considerably more robust and accurate than the earlier Smiths chronometric (clockwork) tachometers used on pre-Commando Nortons.

Key Details

• Smiths instrument number: RSM3003/12
• Black face, chrome bezel
• Scale: 0–9,000 RPM
• Drive ratio: 4:1
• Type: Magnetic (eddy current)
• Fits: Norton Commando S and Fastback, approximately 1968–1970
• Compatible drive gearbox: Smiths BG1508/06 (2:1 reversing — part number 06-0710)
• Also compatible with other early Commando variants using the same 4:1 drive setup
• Freshly serviced and tested — working correctly

Condition: Used original Smiths instrument, freshly serviced and ready to fit. Please review all photographs carefully. Only 1 available.