Every motorcycle has two numbers that matter when you buy: the frame number and the engine number. The frame number identifies the bike. The engine number tells you about the engine. On a classic, the two are often different, and that is where the questions start.
Where to look
- Frame number. Most commonly stamped on the steering head, on the frame tube just behind it, or on a plate riveted to the steering head. On some bikes it is on the frame near the swingarm pivot or under the seat. Look at the owner's manual or a club forum for your model.
- Engine number. Usually stamped on the crankcase, often on a flat pad near the cylinder base or next to the gearbox. On some makes it is on the left side, on others the right.
Clean the area with a soft cloth, use a torch at a low angle so the stamping shows as shadows, and take a clear photograph. Make a pencil rubbing on a piece of paper if the stamp is hard to read.
What to compare
- The frame number on the bike with the number on the registration document and the bill of sale.
- The engine number with any papers that list it, and with the production records if the maker or a club keeps them.
- The number sequence with the model year. A frame number from 1968 on a bike sold as a 1971 is not necessarily wrong, but it needs an explanation.
What "matching numbers" means
A matching numbers bike has the frame and the engine that were fitted together at the factory, as shown by the maker's production records or by an authoritative source such as an owners' club. For some makes, the engine and frame numbers were stamped as a pair. For others, the engine number is not recorded against the frame, and "matching" just means the engine is the right type and in the right number range for the frame.
For collectors, matching numbers add value because they prove the bike is the one that left the factory. But it is not a verdict on condition. A bike with its original engine can still be tired, and a bike with a replacement period engine can be excellent. A replacement is not a flaw if it is declared, correct for the period, and priced accordingly.
Signs of a doctored number
- Stamps that are shallow, uneven or in a different typeface from the rest of the digits.
- Digits that do not line up or have unequal spacing.
- Grinding or filing marks around the stamp, or fresh paint over the area while the rest of the frame is aged.
- A riveted plate with new or mismatched rivets, or a plate that can be moved.
- A number that is not in the factory's range for that model.
Doctored numbers are a classic sign of a stolen or cobbled-together bike. If you suspect one, walk away and do not discuss it with the seller on the spot. If the bike is already in your possession, report it to the police.
What to do with the numbers
- Photograph the numbers and keep the pictures with the bill of sale.
- Ask the owners' club for the factory record or a dating certificate if the make has one.
- Run a stolen vehicle check where one exists in your country.
- Write the numbers into the bill of sale. See papers and proof of ownership.
If the number is missing or rusted away
Some old frames have a number that is hard to read because of paint or corrosion. A specialist can often bring the stamp back with the right method. Do not treat a missing number as an opportunity to get a bargain: it makes the bike hard to register. Ask your registration authority how it handles a bike with an unreadable number before you buy.
