To the OP and anyone listening.
Are you talking about a factory roller block versus a non roller block? The SBC has a soft cut off over of 1987. At that point factory roller blocks were introduced. Passenger cars especially with option performance engines got roller blocks stuffed with the OEM factory roller cam.
But prior to 1996 this is a bit tricky as not all passenger cars got a roller cammed block and roller cam and trucks did not typically get roller cams but their blocks typically have the provisions for a roller cam, these may be anywhere from the raw casting mods to those mods being partially to fully machined. Regardless of the roller mods and level of prep completeness the truck engine in probably 99% of the cases have a flat tappet cam. And of course the roller versus flat tappet is interchangeable in these 1987 and up SBC blocks.
The roller casting mods consist of raised, widened and joined in pairs lifter blocks to support the taller roller lifter and provide a wider and machined flat base for the dog bone that aligns the lifter‘s roller to the cam lobe mostly unsee to the eye is the coolant jacket is slightly modified to provide space for the dog bone. The lifter blocks will accept either flat tappet lifters which sit low in these lifter bores and use the old standard length 7.8 inch push rod. Factory roller lifters are taller sitting proud of the lifter block to make space for their dog bone, these use the short 7.2 inch push rod.
Continuing with the mods there are three bosses cast atop the main oil galley that runs the length of the block’s valley, these are to mount an 8 legged sheet metal gadget called a spider that holds the dog bones onto their lifters. The bosses will be present from raw castings to milled, drilled and tapped or anything in between if the engine came with a flat tappet cam. The 880 block in my S15 came with these milled and drilled but one boss has a busted drill bit in its hole, my guess it was headed for a performance passenger build, inspection pulled it off that line and had it finished as a truck flat tappet cam engine. It was sourced from a 1995 3/4 ton destroyed in a roll over accident.
Continuing on the other block mod for roller cams is at the front where there is a pad cast up that enlarges the older cam gear thrust surface, this is finish machined with 2 drilled and tapped holes when a roller cam is used to mount the thrust plate. As typical if the engine had a flat tappet cam this will exist as either milled but not drilled or tapped to totally finished or somewhere in between. For a flat tappet cam this provides the back of the cam gear thrust surface just as a smaller face did on earlier blocks and such engines use the original 1955 design timing set. If the engine has a roller cam the thickness of the thrust plate has to be accommodated and still mount a cam gear. The plate is almost 3/16ths thick the cam nose is a stepped down diameter that passes through the plate. The cam gear is that much less thickness of the hub and a smaller diameter bolt pattern to avoid crossing timing sets for cam types being used. The thrust plate attaches with two bolts to the block. There are two thrust plates in Chevy inventory the SBC uses the smaller width across the bolt hole centers the BBC uses the larger.
Blocks of this period usually do not have the old fuel pump mount finished because the vehicles they went into used either Throttle Body Injection (TBI) or Tuned Port Injection (TPI) either of which use a inside the fuel tank electric pump. Some blocks will be found with the pump features complete these were originally intended as industrial or marine blocks with a carb and conventional fuel pump. If this has a bolt on cover plate it’s likely the block was redirected to regular vehicle production, if it’s open or has a mechanical fuel pump it likely was originally an industrial of marine engine.
At the rear the leaky two piece crank seal was replaced with a one piece seal in 1986 and on. The crank ends are different and unique to that type of block. The one piece seal block can be modified to use a two piece seal crank with an adapter this does not go the other way in that a two piece seal block cant be modified to accept a one piece seal and crank. The flywheel/flexplate bolt pattern was reduced in diameter for the one piece seal crank so these do not interchange across the crank seal types. The reason is the 305 and 350 carried a small outboard balance weight on the rear hub of the two piece seal crank. The one piece hud is machined round and the outboard balance nub of the earlier crank is now carried on the flywheel or flexplate.
These 1986 and 1987 changes carry on in the L30 and L31 engines of 1996 into today’s crate engines of this type. You will encounter most if not all mods in LO3 and LO5 TBI engines of 1987-1995 and their crate replacements using the flat tappet cam. They occasional are found to some degree in the pre 1986 Crate engines using the two piece seal crank.
I’d hard copy this dissertation and stick it in a notebook for future reference, while not absolutely complete it pretty much knocks these block changes to the Gen I SBC for rear seal and flat to roller tappet cams into a nut shell. The L30 and L31 are also a little different in how they mount the timing cover but when you see it there isn’t a big deal about it.
Bogie
