Main Caps

Please refer to our new Main Caps page at:


A note on thrust bearings (#3 caps:) From the beginning of production (when these engines were designed) in 1958 up until the 1973 model year the diameter of the thrust surface's outer edge (on the #3 bearing) will be approximately 3.470" for the "B" engine and 3.600" for the "RB" engine.  Starting in the 1974 model year, this diameter was increased approximately .280 thousandths to 3.750" for the "B" engine and 3.880" for the "RB" in order the give the thrust surface more surface area. To allow the new larger bearings to fit, the machined recess area in the block webbing and the main cap in which the thrust bearing shells fit was increased an equal amount. This means there are two different #3 caps for both "B" and "RB" engines, one for 1973 and earlier, and one for 1974 and later. In the picture below, we have put two #3 thrust bearing main caps together. The one on the bottom is from an early block, and the one on top is from a late block. You can see the difference in the size of the machined recess area, so remember to specify block year when ordering USED #3 main caps.

We refer to the pre '74 thrust caps as "Early" and the 1974 and later as "Late." It is possible to use the early (smaller) #3 caps in the later blocks, however you will need to use the early bearings and not get the added benefit of the increased thrust surface area. Using the later caps in an early block is also possible, however you will still need to use the early style bearings, since the later style would be too big to fit in the smaller machined recess area. It is possible to have your machine shop enlarge the machined recess in the block and/or cap with a flycutter during line boring to enable use of the later style bearings. Also, all other bearings except the thrust (# 1, 2, 4 & 5) are the same for all years.



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