Matching cases / belly numbers

Identifaction of VIN, case numbers and cylinder heads
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Matching cases / belly numbers


Post by 64duo »

Is it possible to read the case numbers on a complete installed motor with skid plate installed? Since I don't know where to find them, how to interpret them, or relate them to the engine VIN number, can anyone elaborate? I'd like to know if my engine was built as one unit.
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Re: Matching cases / belly numbers


Post by caschnd1 »


I think you'd have a tough time seeing the belly numbers with a skid plate in place. Here is what I've learned about belly numbers.

1) The format of the number is XYY-ZZZZZ.

2) The X in the number is either a 1 or a 2. 1 denotes a 74" motor and 2 denotes a 61" motor.

3) The YY digits denote the year that the cases were machined. Note that they do not necessarily match the year of motor number found above the timing plug on the left case half. Example: In your case the belly numbers could be 163-ZZZZZ if the cases were machined during the 1963 model year but not used on a bike until 1964.

4) The ZZZZZ portion of the number is a sequential number that was stamped into the cases halves during the machining process. This number has nothing to do with the serial number found above the timing plug on the left case half.

If your belly numbers match it means that your cases were originally machined together and matched during that process. If your belly numbers don't match it means one or both of the case halfs was replaced at some point.


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Re: Matching cases / belly numbers


Post by Cotten »


You should be able to see the left case production number. I clean the case first, and then use a mirror and flashlight.
The right isn't so easy ( however occasionally they can be found duplicated within the cam chest).
Look for a single digit stamped on the top of the rear motormount portion of each case. A missing stamp might indicate a replacement.


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