Ford Small Block Rotating Assembly

When the small-block Ford evolved to a 4.00-inch bore, increases in displacement from then
on were found with increases in stroke. The 302ci small-block achieved its displacement via
revised pistons, rods and crank. All three are different and are not interchangeable with the
221, 260 and 289. The 351W engine meets its displacement objective by increasing the block
deck height and corresponding stroke. The Boss 302 engine differs from the standard 302
significantly in that it utilizes a forged steel crankshaft, 289 High Performance style connecting
rods and forged pistons. The 289 High Performance rod and Boss 302 rod interchange without
any modifications because they are basically the same rod. The Boss 302 rod is the same
basic C3AE rod forging as the 289. However, rod bolts are spot-faced 3/8-inch bolts. There is
also an available Trans-Am rod with cap-screw bolts for the Boss 302 engine.
The 351C, 351M and 400M engines, distant cousins of the small-block series of engines,
employ different crankshafts, connecting rods and pistons. While the 351C, 351M and 400M
are all of the 335-series engine family, they differ significantly internally. The 351C has a
different crankshaft, connecting rod and piston than the 351M and 400M because the M-series
engines have a taller block deck than the 351C, even though bore and stroke are the same.

Ford utilized surprisingly few crankshaft types in small-block engines. The 221, 260 and 289ci
engines all used the same cast iron crankshaft, making this crank widely available. While it
might be easy to assume that the 289 High Performance engine had the same type of forged
steel crankshaft also incorporated in the Boss 302 engine to come years later, exactly the
opposite is true. The 289 High Performance engine used the same cast iron crank as the
289-2V and 4V engines - with the only exception being that it was Brinell tested for toughness
and was supported with heavier main bearing caps. It was not a high-nodular iron crank, but
simply the best of the standard nodular iron lot.
    The standard 221, 260 and 289 crank is identified by observing a 1M casting number on the
forward most counterweight. The 289 High Performance crankshaft is also identified by the
same 1M casting number, sometimes with a letter K or a Brinell test mark stamped nearby.
Dimensionally, the 289 High Performance crankshaft is exactly the same as the standard
crank. Care must be exercised in this regard because it is easy to fake a 289 High
Performance crankshaft by simply adding the K or Brinell test mark to a standard crankshaft.
    Ford Crankshaft Identification Casting Marks  

All 221/260/289/302/351W
crankshafts have a marking
like this for identification.
This is a "2M" 302 crank.
The 221/260/289 engines
are "1M". The 351W is a
"3M" crank.
  The 302s cast iron crankshaft is identified with a 2M in the forward most counterweight. This
crank is not interchangeable with the 221, 260 and 289.
221/260/289/302/351W/Boss 302 Crankshaft Identification Chart
  Ford 351C Crankshaft  
The 351W cast iron crankshaft is easy to identify by observing the 3M on the forward most
counterweight. A forged steel crankshaft was never available from the factory for the 351W.

Boss 302
The Boss 302 engines crankshaft is a forged steel unit specific to this engine only. This crank
is identified with a D0ZE-A and 7FE-8 in the forward most counterweight. These cranks were
cross-drilled in 1969 only.

One thing the 351C, 351M and 400M have is common is the use of a cast iron crankshaft in all
applications. Standard 351C cranks are marked 4M and have 3.50-inch stroke. Boss 351
(1971) and 351 High Output (1972) cranks are marked 4MA and are Brinell tested. A 351M
can be stroked to 400ci with the installation of a 400M crank.
    This is the 351C
cast iron crankshaft
marked "4MA"
(arrow) as shown.
  Ford Crankshafts
Fortunately, the performance enthusiast isnt limited to the factory pieces of yesterday. Today,
the aftermarket offers a wealth of high-performance crankshafts designed for street and
racing applications alike.  302/351W Ford crankshafts are available machined from
 6415 raw steel forgings. These cranks feature high-speed oiling
systems, precision-ground rod and main journals, and large fillet radii. Some 351W cranks
have knife-edged counterweights and pin-lightening holes. The journals are polished and
nitrate hardened. This reduces friction and heat. Whats more, the 351W journals are finished
to accept 0.940" wide steel connecting rods.


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