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Karri Weston
How to Identify and Calibrate Smiths Chronometric Speedometers
Smiths Chronometric Speedometers are classic instruments that were used on many British motorcycles and cars from the 1930s to the 1960s. They are mechanical devices that measure the speed of the vehicle by counting the rotations of a magnet inside a coil. The speed is indicated by a pointer that moves along a dial with a scale of miles per hour (MPH) or kilometers per hour (KMH).
Smiths Chronometric Speedometers have a reference number on the dial that indicates the model, the maximum speed, the direction of rotation, and the turns per mile (TPM) or turns per kilometer (TPK) of the speedometer cable. The reference number usually consists of a letter followed by three or four digits, followed by another letter or a slash and another letter. For example, S467/99/L means:
- S: Smiths
- 467: Model number
- 99: Maximum speed in MPH
- L: Clockwise rotation
- /: Slash indicates TPM or TPK
- L: 1280 TPM
The reference number can vary depending on the vehicle and the market. Some speedometers have different letters or numbers for different models, maximum speeds, directions of rotation, or TPM or TPK values. Some speedometers have no slash or letter after the slash, which means they have a standard TPM or TPK value of 1000. Some speedometers have an N instead of an L after the slash, which means they have a non-standard TPM or TPK value that is not indicated on the dial.
To calibrate a Smiths Chronometric Speedometer, you need to know the TPM or TPK value of your speedometer cable and compare it with the value indicated on the dial. If they are different, you need to adjust the pointer position or change the speedometer cable to match them. You can measure the TPM or TPK value of your speedometer cable by rolling your vehicle over a known distance and counting the cable turns. You can also use a GPS device, a sat nav, or a "Your Speed" sign to check your actual speed and compare it with your speedometer reading.
If you need more information about Smiths Chronometric Speedometers, you can consult these sources:
How to Identify and Calibrate Smiths Chronometric Tachometers
Smiths Chronometric Tachometers are similar to Smiths Chronometric Speedometers, but they measure the engine speed instead of the vehicle speed. They are also mechanical devices that count the rotations of a magnet inside a coil, but they have a scale of revolutions per minute (RPM) instead of MPH or KMH. They are usually mounted on the dashboard or the handlebar of the vehicle.
Smiths Chronometric Tachometers also have a reference number on the dial that indicates the model, the maximum RPM, the direction of rotation, and the ratio of the tachometer drive. The reference number usually consists of two letters followed by three or four digits, followed by another letter or a slash and another letter. For example, RC 134 (RC 1501/00) means:
- RC: Smiths Competition Tachometer
- 134: Model number
- (RC 1501/00): Alternative model number
- 10: Maximum RPM in thousands
- 000: Zero padding
- 4: Ratio of tachometer drive (4:1)
- -: No slash indicates standard ratio
- 1: Clockwise rotation
- 0: Zero padding
The reference number can vary depending on the vehicle and the market. Some tachometers have different letters or numbers for different models, maximum RPMs, directions of rotation, or ratios of tachometer drive. Some tachometers have a slash followed by another letter after the ratio, which means they have a special feature such as a light, a tell-tale hand, or an angle drive. Some tachometers have an EX followed by a number after the model number, which means they are experimental models.
To calibrate a Smiths Chronometric Tachometer, you need to know the ratio of your tachometer drive and compare it with the value indicated on the dial. If they are different, you need to adjust the pointer position or change the tachometer drive to match them. You can measure the ratio of your tachometer drive by counting the turns of your engine and your tachometer cable at a known engine speed. You can also use a digital tachometer or a timing light to check your actual engine speed and compare it with your tachometer reading.
If you need more information about Smiths Chronometric Tachometers, you can consult these sources: