Oldsmobile V-8 Engines. Bill Trovato

       The BTR girdle bolts are torqued to the pan rails with 3/8-inch grade-8 bolts. This ties the pan rail to the main caps and replaces the lack of sufficient thickness in the main webbing. It also ties together the three center caps and studs.

       This four-bolt billet-steel main cap is designed for use in small-block diesel conversions. These caps are available for 2.5- and 3-inch main crankshafts. Generally, you only need the four-bolt caps for mains number-2, -3, and -4. One of the purposes of the four-bolt main cap is to keep the side of the block from spreading. I do not recommend four-bolt caps for thin main-web engines.

       The injector-pump boss on a diesel block hits the timing chain unless it is cleared by grinding or some other method.

       A neat little program on the Cincinnati CNC machine mills the injector pump area. It also mills a pocket in front of the number-1 cam bearing so that a capsulated thrust bearing can be installed to prevent wear between the camshaft and the cast-iron block. Not only does the thrust bearing prevent wear, it allows you to set the lifter-to-lobe relationship exactly where you want it.

      To convert one of these engines for gasoline use, there are only a few minor modifications required. The diesel fuel-injector pump boss must be cleared, due to interference with standard timing chains. This task can be accomplished either by grinding the boss away by hand, machining it away on a mill, or (as I do) milling the area away on the CNC machine for maximum weight removal and the best-possible appearance. All above methods will get the job done.

      The diesel timing chain cover may have to be changed to a standard-type gasoline engine piece; the seal area interferes with some harmonic balancers. Additionally, if a back-grooved cam bearing is to be used, the passage that connects the top of the cam bearing bore to the injector pump hole must be plugged with a .250-inch-diameter dowel. The length of the dowel is unimportant as long as it seals the passage and doesn’t move. I’ve found that 1/2- to 3/4-inch lengths are fine. Chances are you will be making a dowel on the lathe out of a piece of aluminum that will fit the hole exactly, as this is a drilled hole and is not necessarily a precise diameter. This dowel plug has a .001-inch or so press-fit clearance, and is installed in the passage with the cam bearing removed. The dowel is typically driven into position with a long drift punch through the connecting passage in the number-1 cam-bearing oil-feed hole. If a conventional (non-back-grooved) cam bearing is to be utilized, this passage can remain open, because the cam-bearing shell seals the hole.

       Small-block diesel engines are relatively easy to spot. They have a “-D3” code on the block behind the timing cover, along with a rather large “D” or “DX” on the side of the block near the freeze plug area.

      Oldsmobile also made a special high-performance engine block commonly referred to as the “NASCAR block.” These high-performance blocks can still be found, but are very rare. There are many different variations of these, but there are basically two different models. One carries Olds PN 22528096 and features coolant-flow passages between the cylinders. The other carries Olds PN 22527735 and has siamesed cylinder bores, which have no coolant-flow passages between the cylinders and allow for larger bore diameters. The siamesed NASCAR blocks can handle bore sizes as large as 4.350 and still retain ample cylinder-wall thickness. The only concern at that point is the lack of space between the cylinders; this is where head gaskets are challenged to seal, as horsepower and cylinder pressure get higher.

       The pocket that is cut into the camshaft thrust area is cut precisely so that the thrust bearing stays in place. Because approximately .140 inch is machined out of the block to retain the thrust bearing, the cam bearing needs to be driven into the block by that amount minus about .030 inch.

       This late 39-degree 425 block used .921-inch lifter bores and had bronze lifter bore bushings installed that were finish machined to .842 diameter for use with more readily available parts.

       The endmill machines a pocket that is 2.930 × .140 inches deep to allow the Cloyes roller thrust bearing to sit in the pocket without falling out. This DX block has main-bearing spacers. It is best to use a main cap that is the proper size so that the only spacer needed is in the block.

       The timing cover on the left is the stock version found on every gasoline-powered Oldsmobile engine. The timing cover on the right is from a diesel engine. The harmonic-balancer seal protrudes from the front of the timing cover. It is best to check for interference before you glue this cover on. This hits some harmonic balancers, and does not hit others.

      The siamesed-cylinder NASCAR blocks are the rarest, strongest, and most desirable of these high-performance castings. I have seen many of the special high-performance Olds blocks and there seems to be so many variations and inconsistencies, so it isn’t worth discussing them all. I have seen the PN 22528096 “non-siamesed” block have siamesed cylinders. I have seen blocks with 2.500-, 2.750-, and 3.000-inch main-bearing diameters. I have seen each of these blocks with .842-, .875-, and .921-inch-diameter lifter bores, etc. The only way to determine if the block has siamesed cylinder bores is to visually inspect them through the freeze-plug holes. Each block, regardless of part number, must be visually inspected to see exactly what features and dimensions it truly has.

Big-Blocks

      Oldsmobile big-block engines also consisted of three different cubic-inch displacements. They were offered at 400, 425, and 455 ci. With regard to high-performance use, the 455 is the most popular and is used most by Olds enthusiasts.

      Oldsmobile big-blocks have many shared features and dimensions. The bore spacing between the cylinders is the same as all Olds engines at 4.625 inches. The main-housing bores are all set at 3.189 inches on all big-block engines. The deck height (measured from the crankshaft centerline to the cylinder-head mounting surface) is set at 10.625 inches on all of the big Oldsmobile blocks. Most of the factory blocks measure right on that dimension too. The lifter-valley areas in all the big-blocks are very similar and are not considered to be a weak spot. I have never seen a failure in this area. The lifter bores on the 400/425 engines could be .842 or .921 diameter, depending on the application. The 455 engines all retained the .842-diameter lifter bores, and all were designed for hydraulic flat-tappet lifters. The main webs are quite thin and are virtually the same on all models. Forget about four-bolt main-bearing caps; there is nothing to bolt to.

       This number designates a siamesed NASCAR block.

      Older 1968–1970 model-year engine blocks had a casting designation