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Frame and Engine Numbers

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Frame and Engine Numbers
John H Glimmerveen Licensed to About.com

For information about a specific make or model of a motorcycle, the owner must have the frame (chassis) and engine numbers. Unfortunately, different manufacturers use different numbering systems and often place the numbers in odd places.

Later motorcycles (post 70s) typically have a stick-on decal or plate on the head stock. Besides detailing the bike's engine and frame number, the decal will show the makers, the model and year of manufacture. However, the model information can be confusing as machines offered for sale after September (in the United States) will technically be the following year's model.

For example, a motorcycle with a year model stated as 10/1982 on the VIN (Vehicle Identification Number) decal will actually be a 1983 model.

Matching Numbers

Early motorcycles generally had the same number for the engine and frame (often referred to as matching). However, occasionally an engine case (containing the original number) may have been replaced due to damage and will not, therefore, have a number stamped into it. Alternatively, the owner may have stamped the new case to match the frame number; a practice that may be frowned upon, but if photographed and logged properly, will not greatly affect the value. (This is a typical example of when it is imperative to save the old parts.)

Locating Numbers

Locating a frame number on an early machine, especially one that is dirty and in need of restoration (barn fresh for example), can be challenging. However, typically, the number will be found in one of the following locations:

  • Head stock (the most common location)
  • Frame down tubes
  • Lower frame rails (at the side)
  • Stamped onto the plate that carries the swing arm pivot
  • Under the gas tank on the frame's top tube
  • Engine mounting plate (front or rear)

Engine numbers are generally stamped into aluminum cases. The location varies between manufacturers but will be located on the crankcases, just below the cylinder.

Help Through Clubs

Identifying a classic motorcycle from its frame and/or engine number is important for parts ordering or valuation purposes. Willing and able to help in this process are the many make specific clubs. In particular, the UK's Vintage Motorcycle Club Ltd. will undertake a search of any vintage motorcycle for a small fee (no charge if they cannot find the appropriate information).

Assuming the manufacturer is still in business, their web sites are also a good source of information if the researcher is willing/able to spend time sifting through the various pages.

Finally, a word of caution: a classic motorcycle may be listed in a sale as a particular year and model but the prospective purchaser must research the engine and frame numbers to ensure they match the claimed model-a model year error, for instance, can make a big difference to the value of a motorcycle.

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