OldIHC

This is the bore and stroke on both engines in 1955
SD 220   3 9/16 bore x 3  11/16 stroke      7.0 comp ratio   108 HP @ 3800 RPM
SD 240   3 9/16 bore x 4.018     stroke      7.0 comp ratio   131 HP @ 3800 RPM
BD 220   3 9/16 bore x 3/16      stroke      7.5 comp ratio   112 HP @ 3800 RPM
BD 240   3 9/16 bore x 4.018    stroke      7.5 comp. ratio  141 HP @ 3800 RPM
The BD was an updated version of the SD as far as I can read about it they changed the rocker arm shaft and oiling in the head also.

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