From:Tom Van Beek
Subject:RE: 1955 ST165 Piston difference Date:Wed Dec 28 10:55:24 2016
Response to:21695
hi Rob: the piston you have is a replacement one that will work just fine in your ST 165 motor. The piston that was in your engine was from a later "BT" motor which had a different cylinder and carburetor so they notched the intake side to match the port in the cylinder! Either piston will work in the St 165 motor, but the one with the relief was for the 1960 and up engines (165/175). Hope this answers your question! Tom


I just got a replacement piston for my 1955 Harley ST165. The old piston is faintly marked "STD", and there is an arrow with "FRONT" stamped beside it on the crown.

The old piston (which I believe to be the original), has a cutout on the lower rear skirt, looks like to clear the carburetor port sooner. The old piston also has one of the corners outboard of the cutout broken off. Looks to me like this was perhaps a trouble spot?

Anyway, my new replacement piston does not have this cutout. Front and rear skirts are identical length. Does it matter?

I can post pictures, if my description doesn't make it clear enough...

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