Over the years I've noticed that first generation small blocks which are the same (327, 350, SB400, etc) do not always have the same machining processes done to them. After casting, and after the molds are remove, how did the line workers know which holes to drill/tap and not to drill/tap on the SAME KIND OF BLOCK? For example, I just recently taken notice on some of my SB400 blocks that some holes are drilled/tapped and some are not-------------------and this is on blocks which have the same casting numbers! Below are 400 blocks which have the bosses cast for the clutch Z-bar (same on 327 and 350 blocks), but some are not drilled/tapped and some are not. What determines this? All small blocks also have the bosses at the front of the block, which were ORIGINALLY for attachment of 55-57 Chevy front engine mounts (ONLY years used for mounting up front). All subsequent blocks have these bosses, but some are drilled/tapped and some are not. SOME later blocks used these holes for mounting accessories such as pwr str pump brackets. ALL blocks have the boss for an oil pressure passage in the top-front of the block, but some have no hole drilled/tapped and some have the threaded hole, but have a plug installed. Any comments on this? Two SB400 blocks with no holes for the Z-bar stud.
Two SB400 blocks with the holes drilled/tapped.
This block had NO HOLES in the bosses on the left side, which I drilled/tapped for a pwr str pump bracket (the holes in the right bosses were already there).
This is the front oil passage I referred to. All small blocks have the boss for the passage. Some blocks do not have the passage drilled from the front of the block down into the center oil galley and some do, and have 1/8in pipe threads and then a plug installed. On all of my engines that don't have the passage drilled/tapped, I do it and install an oil pressure gauge.
I even did it on the 455 Olds engine in my Cutlass.
Again, my question, why were some holes drilled/tapped on the same engines (even with the same casting number) and some not? How would the engine plant line workers know which to drill and which not to drill?