The R3/R4 Roster Project

The South Bend foundry sent blank blocks to Paxton. Some blocks had no stamps and some had the keystone stamp by the distributor and/or near the forward serial # pad. The keystone indicated an replacement block with narrow water passages between inner and outer cylinders, i.e., thicker cylinder walls. B112 has the keystone symbol with “88” stamped inside it on the rear and B39 has the keystone on both ends. The meaning of 88 is not understood.

Paxton used three places to add markings to these engines.
Heads had a number like “065” stamped at one end or above the center exhaust port. It is believed that the numbers indicate the matched, machined combustion chamber volume in cc’s. We aren’t sure if that stamp was consistently used. B13, B78 and B92 have additional stamps next to “65.” These were in the form of 4 S on B13, 2 4 S and 5 4 S on B92 and 4 4 and 6 4 on B78. Astutely pointed out by Dwight FitzSimons, these stamps follow the format for the head casting date codes used on South Bend production head. S means 1963 when it is present , the first of 2 numbers is the month and the second is day of month. We need many more examples of these head stamps. The “B” number is the assembly number of these engines. Studebaker blocks also use the same casting date code. This code can be found forward of the bellhousing, behind and to the right of the distributor.

The forward machined pad consistently had the B number on it for all engines, factory and aftemarket. The B and the number were small, ¼ inch high. All South Bend factory marked engines got the R3S or R4 number applied in this location in larger characters, like R3SN320 on B47. There were at least 3 engines that went to South Bend, were not factory installed in anything, got R3S stamps and were retrieved by Paxton for aftermarket sales, e.g., B44.

The third place was near the distributor. Some engines have the B number here also. The R3S or R4 number was never here.