An Overview of the Smith’s BG5330 Speedometer Drive Units
Most vintage British motorcycles from the mid-1960s into the 1980s were originally fitted with Smith’s or Veglia magnetic speedometers which are driven by a gearbox unit mounted to the rear hub. A fixed drive ring on the rear wheel hub rotates with the wheel which in turn, rotates the gearbox inner driving gear. As the driving gear engages with the internal driven gear, the direction of the cable receiver is reversed, with the cable serving as the nexus between the speedometer drive gearbox and the instrument.
The majority of most common BSA, Norton, and Triumph twin-cylinder models from 1966-onward are fitted with this type of speedometer drive gearbox, the Smith’s BG5330 series (although the early unit C-range Triumph 350cc and 500cc models were the exception, as they were fitted with rear wheel-driven speedometer drives from 1959-on). Early 1960s models from AJS, Matchless, and Norton also employed rear wheel-driven speedometer drives. I’ll focus on the most commonly seen BG5330 models in this blog.
Several factors are to be considered when replacing a faulty original (or completely missing) speedometer drive unit during a restoration (or refurbishment):
Drive ratio
The BG5330 speedometer drives were available in 1.25:1 (15/12), 2:1, 21/10, or 19/20. The most commonly used ratios are 1.25:1 and 2:1. It is important to determine the ratio calibration of the speedometer that is to be used with a given speedometer drive unit to ensure accurate speed and odometer readings. The two components must be paired together.
Axle hole size
The most common sizes are manufactured to fit 5/8”, 11/16”, and 3/4” axles, or spindles.
Reversing or non-reversing operation
The majority of BG5330 units specified for use on BSA, Norton, and Triumph models are reversing operation.
Rear hub orientation
Most all BG5330 units are fitted to the right, or non-drive side of the hub. The exceptions to this are the 1975 Triumph T160 and Norton Commando MK3 models, which have the speedometer drive fitted to the left side of the hub.
Since the various BG5330 units share the same castings, it is critical that the minor details be determined prior to fitment on the motorcycle. A measurement of the axle hole and visual inspection of the gold-colored felt seal retaining ring is recommended to assure correct fitment and calibration of the speedometer gearbox. The identifiers are stamped into the gold retaining ring.
Now, let’s take a look at the most common fitment applications:
BG5330/164 Fits1971-1974 Triumph, BSA 650, 750 twins and triples with conical hubs and 5/8” rear axle. Also used on the 1976-1978 disc brake hubs. 1.25:1 (15/12) ratio is often paired with Smith’s SSM 5007/00 and SSM 4003/02 150 MPH black-face speedometers. The Triumph part number is 60-3213. BSA identified the same unit as 19-9225.
BG5330/168 Fits late 1967-1970 Triumph 650, 750 twins and triples, as well as the BSA A75 triple with spool hub and 3/4” rear axle. 1.25:1 (15/12) ratio is often paired with Smith’s SSM 5001/06 and SSM 5007/00 150 MPH grey or black-face speedometers. The Triumph part number is 60- 0637. BSA identified the same unit as 19-9221.
BG5330/171 Fits late 1967-1970 BSA twins and 1968-1974 Norton Commando models with 11/16” rear axle. 1.25:1 (15/12) ratio is often paired with Smith’s SSM 3001/02, SSM 3001/09, SSM 5001/05, and SSM 5007/00 150 MPH grey or black-face speedometers. The BSA part number is 19-9217, while Norton used the part number 06-0627.
BG5330/287 Fits 1959-1974 Triumph 500 twins, as well as the 1966-early 1967 Triumph 650 models with spool hub and 3/4” rear axle. 2:1 ratio is often paired with Smith’s SSM 5001/00, SSM 5002/00, SSM 5007/02 120 MPH grey or black-face speedometers. Early unit-construction 350 and 500 twins through 1963 were equipped with Smith’s Chronometric speedometers calibrated for 2:1 drive gearboxes. The Triumph part number is 60-0373.
BG5330/170 Fits 1975 Triumph T160 and Norton Commando MK3 models, with disc brake hubs, 5/8” rear axle and left-side mounting. 1.25:1 (15/12) ratio is paired with Smith’s SSM 4004/00 150 MPH black-face speedometer. The Triumph part number is 60-4403, while Norton used the part number 06-5540.
The Bonneville Shop offers reproductions of the Smith’s BG5330 series speedometer drive gearboxes from two different suppliers, LF Harris and EMGO. The quality and finish of the two reproduction brands is nearly identical, with the EMGO units priced slightly lower. I hope this blog helps answer any questions that may arise when attempting to source the correct speedometer drive gearbox for your application.
