The R3/R4 Roster Project

Markings on Paxton R3 and R4 Engines

This is a somewhat informed dissertation on where and how Paxton and South Bend applied serial numbers to R3 and R4 engines.

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.

Engine Front "B"
Rear "B"
Casting #'s
B5 (Bruffet) yes
yes yes, 88 yes, 88 66 1535479
B8 65.6
B13 Yes ? Yes, 88 Yes,88 65.6
B17 (Bove) Yes Yes Yes, 88 Yes, 88 66.3 1555479
Yes Yes Yes Yes 66.04
B22 (R4)
Yes No No No ? ?
B39 / R3SK309
Yes Yes Yes Yes ? ?
B43 / R3SM306
Yes ? ? ? ? ?
B44 / R3SK315
Yes Yes No No 065 1555479
B46 / R3SM306
Yes Yes No No ? ?
B47 / R3SN320
Yes Yes Yes Yes, 88 ? ?
R3SB54 ? ? ? ? ?
B67 R3B67 R3B67 ? ? ? 1543971
B69 ? ? ? ? ? 1555479
B76 (R4)
B76 R4 B76 R4 No Yes, 88 ? ?
B78 (R4)
(P. Johnson)
Yes Yes No No 65. 1555479
B79 (R4)
(K. Bell)
B79 R4 ? ? ? ? ?
B85 Yes Yes No No ? 1555479
Yes Yes No No 65. 1555479
Yes ? ? ? ? 1555479
Yes Yes No No na na
Yes Yes Yes Yes, 88 na na
Yes Yes No No na na
N305 (Parker)
No Yes ? ? na na
na na na na 66.0 na
* driver’s side / passenger side heads are different numbers. Prototype R3 heads.

Every Paxton engine and set of heads wants to be accounted for here.