Vintage Whizzer Piston Information

Discussion in 'Whizzer Motorized Bicycles' started by doc-detroit, Jun 8, 2010.

  1. doc-detroit

    doc-detroit New Member

    Below is a portion of an e-mail that Quenton recently sent me that should be helpful to all:

    "Pistons for vintage Whizzers usually have either VMJ2151 or VMJ2182 cast inside. The numbers aren't the part numbers, however the early VMJ2151 was part number #2151, and the later light weight pistons [VMJ2182] were #2182 for the .005" O.S. All early pistons were cast with the VMJ2151 regardless of size, and all later pistons were cast with the VMJ2182 number in all sizes.
    The original parts books doesn't list it exactly correct, for example part number #2182 is a .005" O.S. including the rings. and the casting numbers inside the piston would be VMJ2182, but the stock bore piston wasn't listed in the book but still had the same VMJ2182 number cast inside. The parts book only lists the light weight piston in .005" and .010", however I have them in original boxes in STD bore, .005", .010", .020", and .030", all with the VMJ2182 casting number.

    When the piston and cylinder have the same letter it usually means it is the stock cylinder and the original matched piston. The letters are minor size differences of the piston. "A" means the piston is between 2.2425" and 2.2440". "B" means it is between 2.2430" and 2.2455". "C" means the piston is between 2.2435" and 2.2460". "D" means the piston is between 2.2440" and 2.2465".

    Unlike today's Whizzers the vintage motors "matched" the piston to the cylinder, and is the reason for the lettering on the piston & cylinder. The vintage motors also made it possible to install a lettered piston in order to create a tighter fit. As an example if the original piston was a "B" version, one could hone the cylinder slightly and install the next lettered piston. "B" could be subed with a "C" or "D" and reduce the clearance slightly. Of course the "lettered" pistons are now impossible to find.

    Here are numbers concerning O.S. piston size, .005" O.S. ranges from 2.2475" to 2.2500". .010" ranges from 2.2525 to 2.2550". .020" ranges from 2.2625" to 2.2650", etc

    The clearance between the piston and cylinder must be measured below the wrist pin, not on the front or rear skirt of the piston. The clearance should be approx. 004", and if over .006" the cylinder should be bored to the next size. If a motor is run with slightly loose bore it will usually smoke a little but will work OK for a long time, but if the bore is too worn the piston will "rattle" and should be replaced with the next O.S.

    Unless the piston is stamped on the top with a size it is a stock bore. .005" O.S. pistons will have .005 imprinted. The .010" O.S. will have .010 stamped in the top of the piston. The .020" O.S. piston will have .020 stamped on the top of the piston, etc, etc."

    Quenton, thank you.