The generation of engines from 1964 to 1990 consisted of big blocks
and small blocks. Actually the big block first appeared in 1965. These
two engine types are almost identical, with the big block having a higher
deck than the small block. The bore centers are the same, since the only
differences between the small-block and big-block Olds blocks are the deck
height (9.33" and 10.625", respectively) and the main journal
size (2.5" and 3.0"; diesel 350 used BB size mains, however).
Theoretically, you could also destroke a big-block with a diesel crank.
With the later 400 block, you would get a 319 CID big-block. But why bother?
Many internal parts interchange, but it is best to keep the big block
parts on the big block and the same for the small block.
The large oil fill tube on the front of the engine, sticking up from
the timing chain area, is a dead giveaway that it is an Olds engine.
The distributor is found at
the back of the block and it does not go through the intake manifold, but
right into the block. Also the spark plugs will be above the exhaust manifolds
with no need for heat shields.
Original paint color can help identify an engine. However, since paint
is easily changed, it should be used as supporting evidence, not as absolute
indication of engine lineage.
The VIN stamping on the left most side of the block, on the driver's
side, just below the cylinder head, toward the front. The pad is part of
the engine and will indicate the year of manufacture, but that is usually
rusted beyond recognition, and it can be changed by restamping. If the
engine was replaced under warranty, the pad may be blank. Rubbing alcohol
and Q-tips help to remove the grime and grit from the stamping.
The Block Code and/or Head Code can give you an idea, but some codes cover
many years. Other than that, there is no method of determining the year
of manufacture of an Olds block. The day of the year of manufacture is
the big number right by the distributor hole.
Olds didn't cast the displacement into the side of the blocks until they
went to the light weight design in 1977. The 1977 and newer blocks will
have the cubic inches cast in large raised numbers right above the center freeze
plug. The 307 will be in liters (5L), and a diesel engine will have the
letters "DX" on it. The engine VIN letter will also be cast
into the side of the block.
A bodies use a notched valve cover set. The drivers
side and the passenger side have reliefs in the back areas to allow access
to them with A/C and power brakes.