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

0.020 inch, the next available oversize.
The machinist first bores the cylinder
with the worst wearltaper because it will
establish the maximum oversize for all
the cylinders.
Diai-Bore Gage or Micrometer Method-
When using a bore gage or micrometer
to measure taper, measure the point of
maximum wear immediately below the
ridge. Because wear will be irregular, take
several measurements around the bore to
determine maximum wear. To determine
taper, subtract the measurement at the
bottom of the bore from that at the top.
Ring-and-Feeler Method-Measuring bore
wear with a piston ring and feeler gage
is going about it indirectly. When using
this method, you are actually comparing
the difference between the circumferences
of the worn and unworn bore. The accuracy
of this method is less the more irregularity
a cylinder is worn, however it is
accurate enough to determine whether
you'll need to bore and install oversize
pistons or clean your pistons, hone the
bores and install moly rings.
To use the ring-and-feeler method,
place a ring in the cylinder and compare
the difference in ring end gaps with the
ring placed at the bottom of the bore and
with it at the top of the bore-immediately
below the ridge. Use the same ring.
While it doesn't need to be a new one, it
must be square in the bore to get an
accurate reading. To square the'ring, push
it down the cylinder with a bare pistonno
rings-to where you want to check
ring gap. Measure the gap with feeler gages
and record the results. After measuring
the ring end-gap difference, use the
accompanying chart or graph to determine
bore taper. Taper is approximately
0.3 times ring end-gap difference.
How Much Taper is Permissible-To decide
how much taper your engine can
live with, you'll have to ask yourself how
many more good-miles you want out of
your engine. Do you want it to last
10,000, 20,000 or 100,000 miles before
oil consumption takes off If your engine
has excessive taper, even new rings will
quickly fatigue and quit sealing. They
must expand and contract to conform to
the irregular bore during every stroke.
Consequently, they lose their resiliency,
or springiness. Also, because ring gap
must be correct as measured at the
bottom of the bore, in a tapered bore the
gap will be larger at the top where compression
and combustion pressures are
highest. Consequently, these pressures
will be reduced slightly because of
increased blowby through the wider
Here's a cylinder that's just been sleeved.
All that is required to finish this sleeving job
is to trim sleeve top flush with block deck
surface.
Measuring piston-to-bore clearance with
feeler gages. If it's 0.008 inch or more,
rebore.
ring gap.
Therefore, if you just want a "Band-
Aid" job on your engine so it will go
another 10,000, or maybe 20,000 miles
before it's right back where you started,
you can get away with reringing a block
with some cylinders having as much as
0.010-inch taper. If you are using the
ring-and-feeler method, rebore if taper exceeds
0.008 inch. This is because this
method masks some forms of wear. However,
if your object is to have a truly rebuilt
engine, don't merely rering if taper
exceeds 0.006 measured by the dial-boregage
or micrometer methods of checking,
or 0.004 inch by the ring-and-feeler
method. Remember, taper gets worse
with use, never better. It's best to start a
rebuilt engine's life with a straight bore
and new pistons if you want maximum
longevity.
SLEEVING AN ENGINE
A sleeve is basically a portable engine
cylinder. It is used to replace or restore
a cracked, scored or otherwise
damaged bore that can't be restored
by conventional boring and honing
techniques. An expenditure of WI~Y
$20 to $30 for sleeving a cylinder
can save you the cost of a new or used
engine block. A sleeve is a cast-iron
cylinder which is slightly longer than
the length of the cylinders In the
engine it is made for. It has a smaller
ID than the original bore for finishing
stock and a wall thickness varying
from 3/32 to 118 inch.
To install a sleeve, the damaged cylinder
must first be bored to. s size
0.001" less than the OD of the sleeve.
Rather than boring all the way to the
bottom of be bore, the boring machine
is stopped just short to leave a step or
shoulder for locating the sleeve. The
step and the interference fit of the
sleeve prevent it from moving around
after the engine is back in operation.
Some rebuilders leave more than
0.001'' interference between the sleeve
and the block. The problem is this
overstresses the block and can distort
neighboring cylinders, consequently
the 0.001" figure should be adhered to.
When an engine is ready to be
sleeved, it shou!d be evenly warmed up
using a torch, furllace or whatever so
the block will grow. At the same time
the sleeve is cooled to shrink it-a refrigerator
freezer works geat for this.
The sleeve will almost drop all the way
into the cyligder, however it will
quickly rise to the same temperature
as the block, assuming its interference
fit. Then it must be pressed or driven
in the rest of the way and sealed at
the bottom. Some shops don't bother
with heating and cooling. They drive
the sleeves in all the way. The excess
length of the sleeve protruding from
the block is trimmed flush with the
deck surface. The block is now restored
and the sleeved cylinder is bored to
match other cylinders.
Piston-to-Bore Clearance- All this talk
about whether to bore or not to bore
may turn out to be purely academic. The
main reason for not wanting to bore an
engine is to avoid the cost of new pistons,
a legitimate reason considering they cost
at least $10 to $20 each. If your old pistons
are damaged or worn to the point of
BLOCK RECONDITIONING 55