How To Rebuild Your Ford V-8 351C-351M-400-429-460.pdf - Index of

I
I
Pop-up '71 351C Boss piston and flat-top '72 HO piston give compression ratios of
11.3:l and 9.2:1, respectively. Both are forged, whereas standard pistons are cast.
Piston at right is TRW's forged version of the standard 351 C cast piston.
forged for added strength. Additionally,
the Boss uses a pop-up type 1 1.3 : 1 piston.
A pop-up, or dome is a lump formed into
the piston top to reduce combustionchamber
volume for increased compression.
The '72 HO, a low-compression version
of the '7 1 Boss, uses a flat-top forgedaluminum
9.2:l piston. It is similiar in
appearance to the cast version of the
351C piston.
351M/400-351M and 400 pistons are
cast-aluminum, fit the same diameter
bores and are flat-top with two valve
reliefs. The major difference is compression
height, the distance from the wristpin-bore
center to the top of the piston.
Compression height for the 351M is
1.947 inches. The 400 is shorter at 1.647
inches to compensate for its longer stroke.
As a result, these pistons are not interchangeable.
Remember, the 351M and
400 engines use the same connecting rods.
Consequently, a 351M piston installed in
a 400 would stick out the top of its bore
or crunch against the bottom of the cylinder
head as the piston approaches TDC.
On the other hand, a 400 piston installed
in a 351M would stop far short of the top
of its bore at TDC and would hit the
crankshaft at the bottom of the stroke.
429-2V, 4V and 4604V-The 4291460
piston description is similar to that of the
351M1400. They are cast-aluminum, fit
the same bores, have two intake-valve
reliefs and have different compression
heights. 429 and 460 engines also use the
same connecting rod. The 460's pistons
are dished to achieve the desired compression
ratio. I'll discuss how an engine's
compression ratio is determined later.
429 CJ, SCJ, Police and 460 Police-Other
than the 460 Police, 429, CJ, SCJ and
Police pistons differ from the standard
piston. The 460 Police engines use conventional
passenger-car pistons, 429 CJ
and Police-car pistons are cast as originally
installed, however their design differs
from that of the standard 429 piston.
Rather than having two intake-valve
reliefs, 429 CJ, SCJ and Police-car pistons
have one valve relief. Consequently, an
originally installed piston must be installed
in the same cylinder bank it came in be-
cause it has an offset wrist pin-the pin
centerline is 0.0625 inch to the right of
the piston center-line. This means the
piston can't be turned around to clear
the intake valve for installing in the
opposite bank as is possible with a piston
having no pin offset. Fortunately, all
429 CJ, SCJ and Police service pistons are
manufactured without this offset making
it possible to install the piston in either
direction. Ford services the CJ and 429
Police piston with the SCJ piston. Its
design is the same with one major exception-it's
forged.
CRANKSHAFT, ROD
AND PISTON MATCHING
What if you're replacing your connecting
rods, pistons and crankshaft with
those from another engine Some interchanging
is possible due to the 35 1 M/400s
and the 4291460s using the same blocks,
however this is about it. To do any interchanging,
you must be aware of the basics.
Otherwise, you can end up with a basket
of expensive junk.
For instance, crankshaft throw, connecting-rod
center-to-center length, piston
compression height and deck clear-
ance must be compatible with the block's
deck height. For a given stroke crankshaft,
a longer rod will cause a given
piston to operate higher in its bore. A
shorter rod would cause the same piston
to operate lower in the same bore. Piston
compression height is very important
here because of the 351M1400 and 4291
460 situations. As compression height is
increased-the pin bore is moved down in
relation to the piston top-the top of the
piston will operate higher in the cylinder
bore. Reducing compression height moves
it down. The last item, deck clearance, is
simply the measurement from the piston
top at TDC to the block deck or cylinderhead
gasket surface. This clearance is
necessary to prevent a piston from
hitting the cylinder head. The question is,
"How does all this relate to swapping
parts"
The sum of the crankshaft throw, connecting-rod
length and piston compression
height must not exceed a block's deck
height, otherwise serious engine damage
will result. This is particularly true if it is
exceeded by more than the specified deck
clearance. In this case the piston will
come higher than the deck surface and
impact against the cylinder head. On the
other hand, if the sum is considerably
less, you'll have a very underpowered
engine due to a too-low compression ratio.
One final and vital factor that must be
considered when changing bottom-end
components is balance. You don't want
undue engine vibrations. Chances are this
won't be a problem as the components
that can be interchanged are balanced to
work with each other, however it certainly
wouldn't hurt to have bottom-end
components checked for proper balance.
This is particularly important in high-performance
applications. Many engine machine
shops are equipped to do this, and
at very reasonable prices.
VALVE-TRAIN DESIGN
Variations in 335 and 385 valve trains
are restricted mostly to the rocker-arm
designs and how they are stabilized, or
guided. To operate a valve, a rocker arm
must rock only in the plane of the valve
stem and the pushrod. Ford uses two
basic rocker-arm styles and guides them
in three different ways.
Valve-Stem-Guided-1968-71 4291460s
are the only 3351385 engines using valvestem-guided
rocker arms. The rocker-arm
pivot or fulcrum is spherical at its rockerarm
contact surface. Consequently, the
only thing keeping the rocker arm from
pivoting in all directions is the rockerarm
rails, thus the name rail-type rocker