Late-model blocks have their casting numbers on the rear ledge of the case along with the original size of the engine indicated in liters. This 350 block (5.7 liters) features a one-piece rear main seal and was obviously cast in Mexico.
Since the mid-1980s, many late-model small-blocks rated the engine size in liters (such as 4.3L, 5.0L, or 5.7L), and this number is cast into the ledge at the rear of the block on the driver side. Also, on late-model blocks, the last three digits of the block casting number are cast into each side of the block between the freeze plugs in large, easy-to-read numerals.
A number of changes to the blocks have occurred over the years. Some changes to keep in mind are: In 1955, the 265 block did not have an oil filter. The 265 also used a slightly different method of engine lubrication in 1955 and 1956. These 265 blocks feature two oil passage holes in the block at the rear cam journal to feed oil to the lifter galleries and heads. This requires the use of a rear cam bearing that has two matching holes in the cam bearing and a camshaft that has two flats ground into the rear journal of the cam itself. If you use an incorrect rear cam bearing or use a camshaft without the two flats in the rear cam journal, oil does not circulate to the lifter galleries and won’t get to the heads. This system was changed in 1957. The later blocks have an annular groove in the rear of the block itself and use a different-style rear cam bearing and rear cam journals without flats.
This early 283 block from 1955 to 1961 (left) was cast without a scallop shape at the bottom of the cylinder bores. This limits the crank stroke to 3 inches. Later small-blocks have the scallops at the bottom of each cylinder barrel to allow the use of longer cranks (right).
Block Casting Numbers
The 1961 283 block also had a tower in the front of the lifter valley. This tower connected to the oil filler tube that was present in intake manifolds until 1969, when the block casting was changed and the oil fill location was moved to the valve covers.
This 1967 283 block shows the rear of the block, which at that time had a cast-in tower and baffle assembly mounted in the lifter gallery for a crankcase ventilation system. Block castings were changed in 1969 to remove this tower.
Some blocks will show a number such as “010” on the rear of the block or on the front under the timing cover. This means that 1-percent additional nickel was used in the casting process. Sometimes only a single “020” is found, meaning that 2-percent additional nickel was used.
If you are using a manual transmission and mechanical clutch linkage, you may need to mount a ball and stud to the block in order to use the linkage Z-bar. Make sure that the block you use has the mounting boss in the correct location for your vehicle application. This block shows two; one near the filter boss and the other just to its left. Some blocks have multiple locations; some blocks have none. If you are updating to a hydraulic clutch or an automatic transmission, you don’t have to worry about this.
Chevrolet changed the location of the oil dipstick on different applications. Many simply went through the oil pan rather than the block. Other blocks may be machined for one on either the driver’s or passenger’s side near the head mounting deck. This block shows a driver-side-mounted dipstick.
The rear main seals of blocks used a rope seal from 1955 to 1958. During 1959 through 1985, they took a two-piece neoprene lip rear main oil seal. The circular, one-piece rear main seal was introduced in 1986 on production engines, although some replacement motors, crate engines, and Bowtie blocks still used two-piece rear main seals and matching cranks.
Front engine mounts were used in early blocks and were later replaced with side-mounted engine mounts. Some of the early blocks have no bolt bosses cast into the side of the blocks for engine mounts. If your block is from the 1950s, check it to make sure you use the correct front or side engine mounts.
The 265 and 283 blocks made from 1955 to 1961, which used 3-inch-stroke cranks, do not have any reliefs cast into the block where the block webbing meets the bottom of the cylinder barrels. The 1962-and-later 327 blocks have reliefs cast into the lower end of the block where the barrels meet the block webbing. This allowed the use of the longer 3.25-inch-stroke 327 cranks. If you have an early 265 or 283 block that does not have these reliefs, it is difficult to install a 3.25-inch or longer stroke small journal crank.
Small journal blocks made from 1955 to 1967 used 2.30-inch main bearing journals with a road draft tube boss at the rear of the lifter valley that mounted an oil separation canister in the lifter valley, which connected to the block and the road draft crank-case ventilation tube. Also, a tube cast into the front of the lifter valley mated to an oil fill tube on the front of the intake manifold. The 1969-and-later blocks eliminated the oil fill tube and the road draft tube. The oil fill tube on the front of the intake manifolds was also eliminated. Crankcase ventilation and the addition of oil were accomplished through the valve covers.
Many of the V-8 Chevy IIs made in the 1960s with 283 or 327 small-blocks have a unique block. Engine clearance in these 1962 to 1967 vehicles required that the oil filter boss on the driver’s side be moved up or recessed up in the block. In 1965 to 1967, the dipstick hole in these blocks was plugged and the dipstick tube went directly into the unique Chevy II oil pan.
If you intend to use a manual transmission in your vehicle, along with mechanical clutch linkage, and if the clutch linkage Z-bar requires a block-mounted pivot ball and stud, then the block you use must have a threaded bolt boss (usually near the oil filter–mounting boss) for the pivot ball and stud. Chevrolet placed this threaded boss on the block in a number of different locations. Some blocks have no threaded bosses; some blocks have only one threaded boss; and some blocks have a variety of bosses to fit a number of engine and vehicle combinations. Make sure the block you use has a threaded boss for the pivot ball and stud where you need it. An alternative is to use an automatic transmission or to use a hydraulically operated clutch linkage assembly.
The 350 engine was introduced in the 1967 Camaro. This 1967 Camaro 350 block used a larger main journal (2.45 inches) crankshaft. Other changes were made in the block webbing and bearing saddles to increase strength and to accommodate the larger journal cranks. Other large journal blocks in different displacements were introduced in 1968-and-later model years.
From 1970 through 1980, 400 small-blocks used 2.650-inch main bearing journal crankshafts and a slightly shorter connecting rod (5.565 inches). These blocks also used siamesed cylinder barrels with 4.125-inch standard bores in order to fit the increased cubic-inch displacement inside the original outside dimensions of a small-block V-8 case. These 400 blocks used externally balanced vibration dampers, flywheels, and flexplates.