From:Dr. Pepper Electronic:wysongslkpan-A-yahoo.com
Subject:RE: 165/175 jug, etc. Date:Sun Oct 16 08:49:18 2011
Response to:16456
Chuck, The jug,piston,rod,head are the same size,the later rods have needle bearings and can't be rebuilt and early one have rollers.There is a spacer that is used on the 175 to compensate the longer stroke,it goes under the jug~~without it the piston will hit the head.If you take a 175 and put 165 flywheels in and leave the spacer out it should make it a stock 165 with no loss of compression and the other way is to take a 165 and put 175 flywheels and the spacer in and then its a 175~~~Am I correct Mutt ?
See picture of spacer,I found this out the hard way when I did my motor

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Since the 175 has longer stroke, how about the 175 cylinder height? How about the 175 cylinder head? My 175 was destroked with more available 165 flywheels during a rebuild, and wonder if it lowered the compression in the original cylinder? If so, how about milling the head to compensate?

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The 165 175 have the same bore, the 175 has a longer stroke.

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I need to replace the pistong rings on my 1963 175BTH motor. I can only find listings for new 125cc and 165cc rings on sites such as harleyhummer.com. Are the piston and rings in a 165cc and 175cc the same?