How To Rebuild Your Small-Block Ford.pdf - Index of

You'll find the crankshaft casting number on
the side of the front throw. 2M indicates this
is a 302 crankshaft.
318-in. rod bolts and spot-faced seats make Boss 302 connecting rods much stronger than standard
5116-in. bolted broached-seat rod at right. The HP289 rods use the larger bolts, but rodsare broached.
achieved its additional displacement by a
114-inch throw increase, giving a 3 .SO-in.
stroke. A concurrent 1.274-in. increase in
the 351Ws block deck height accommodated
longer rods and pistons with more
compression height.
Crankshaft Replacement-If your connecting
rods and pistons appear to be in good
shape, but your crank can't be reused,
you'll have to replace it with a crank
having the same stroke and journal diameters
as the one originally installed in
your engine. If your engine displaces 221,
260 or 289 cubic inches you can use a
crank from any of these engines because
Compession height of a 351W piston is 0.136 in. higher than a 302 piston. A 351W piston installed
they have the same stroke and journal in a 302 block will protrude above the gasket surface.
sizes. Not so with the 302. Boss 302 or
351W engines. A 302 crank has to be
replaced by another 302 crank. Likewise
with the 351W.
CONNECTING RODS
All 221,260 and 289 engines use identical
forged-steel connecting rods. Centerto-center
length, as indicated in the chart
is 5.1 55 in. This length is the distance
between a connecting rod's wrist-pin and
bearing-bore centers. These rods use 511 6-
in. bolts and nuts to retain the caps. The
standard 302 rod was shortened to 5.090
in. so the cylinder-block deck height could
be maintained while increasing crankshaft
stroke. The 302 retains the 5116-in. bolts
with one exception. A special heavy-duty
rod was fitted with 318-in. bolts and nuts-
C90Z-6200-B- but these are no longer
available as replacement parts. So few
were manufactured that you might as
well forget them.
The Boss 302 rod is unique in that it
retains the 5.155-in. center-to-center
length of the previous small blocks. Deckheight
clearance is maintained by reducing
piston compression height-the distance
from the center of the wrist-pin bore to
the top of the piston. Boss 302 and HP289
connecting rods have something in
common other than their center-to-center
lengths. Both use 318-inch bolts. The one
difference between them is how they are
machined under the bolt heads. The
These 302 pistons illustrate changes in compression ratios and clearance volumes over the years.
Left to right, the '68-'72 piston is slightly dished whereas the '73-'76 piston is more so, resulting
in a one-point lower compression ratio with the same cylinder head. The 3021351W cylinder head
with its large combustion chamber requires a flat-top piston to achieve an 8:1 compression ratio.
HP289 rod is broached like the conventional
rods whereas the Boss 302 rods are
spot-faced. This makes the Boss rod slightly
stronger because of less stress concentration
on the inboard side of the bolthead
seat. So, if your are building an
engine you plan to operate in excess of
6,000 RPM, consider using these rods.
The HP289 rod-C30Z-6200-C-has been
replaced for service by the Boss rod-
C9ZZ-6200-B. There are, however, two
problems with using these rods. First,
they cost over $50 each! This is too steep
unless you're building an all-out racing
engine. Then it's just steep. The other
problem is they are rare and consequently
are hard to find.
Ford hgh-performance parts are
extremely hard to find and they are very
expensive.
Not only was the 351W block and
crankshaft changed extensively, so were
its connecting rods. They were increased
in length to 5.956-in. The big-end diameter
is maintained, however the bearing
inserts are thinner to accommodate the
larger 2.3 1 1-in. crankshaft journals. Like
its crankshaft, the only place you can use
351W rods is in a 351W block. The 351W
rod also uses the 318-inch bolts.