From:Dr. Pepper
Subject:RE: RE: RE: 165/175 jug, etc. Date:Sun Oct 16 12:39:37 2011
Response to:16458
Holy smokes,This info was very helpful not only did it answer my problem but I printed it out for future generations that read my service manuals, Thanks Mutt

The 175 cc cylinder measures 3.555" from gasket surface to gasket surface. The 165/125 cylinders measure 3.478". If ya use 125/165 flywheels in a 175c jug, the piston crown will be about .250 from the gasket surface (generally, the piston crown should be within .020 to .040 from the gasket surface on any stock motor) , making your compression like what 5:1? If you put in a stroker plate, it would make the compression ratio even lower, like 4:1.
In 1962 when the 175cc came out, the Ranger and the BTU Pacer were still 165cc. The Scat(BTH) and the regular Pacer (BT)which were 175cc, used that stroker plate to raise the 1962 cylinder. In 1963 the 175cc got it's own cylinder, so the plate was not used any longer.
If you run the 165 wheels with a 175 cylinder, you would need to machine the head to actually sit down in the bore some, to achieve the desired clearence between the combustion chamber surface and the piston crown, to obtain teh proper 6.6:1 compression ratio. While you are machining that, you can also machine the much needed "squish band" into the combustion chamber surface, where the combustion chamber squish band is 3/8" wide all the way around and has a .078" clearence between it and the piston crown. You would also have to take into consideration if you use a head gasket or not before ya do the machine work.


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

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?

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

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 Are the piston and rings in a 165cc and 175cc the same?