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

Monitoring engine functions under simulated
road-load conditions is a good way to
determine whether your engine is "tired"
and needs rebuilding.
measure it. Judging power loss can be
done with a chassis dynamometer. Using
the "seat-of-the-pants" method is inaccurate
because the wearing-out process and
accompanying power loss are too gradual.
If you suspect your engine's performance
is suffering, but oil consumption is
normal, give your engine a thorough
tuneup. Choose a reputable tuneup shop
with a chassis dynamometer. It measures
power at the drive wheels while critical
engine functions are being monitored.
You can compare horsepower readings
before and after the tunetip. Just make
sure that the tuneup shop you take your
car to can give you horsepower readings.
Many don't, or can't. If the tuneup cures
the problem, relax and read the rest of
the book for entertainment just to see all
the fun you missed. If it doesn't, you'll
have to do some further investigation.
CAUSE OF POOR PERFORMANCE
Let's review some possible causes of
performance loss. The first suspect is
piston-ring and cylinder-bore wear. These
cause increased oil consuniption. If blowby
is excessive, there will be an accompanying
loss of conlpression and combustion
pressure. The engine produces less
power and gets worse fuel economy. If
your engine is "hurting" in both the oilconsumption
and performance departments,
chances are the problem is with
the rings and cylinder bores. If this is not
the case, look further.
If your engine is giving poor gas mileage
and power, but is OK on oil consumption,
suspect the valve train. This assumes the
carburetion and ignition systems are in
good order. Problems can include a blown
head gasket, burned exhaust valves, worn
camshaft lobes and lifters, and carbon
buildup in the combustion chamber
Blown Head Gasket-A blown head gasket
causes compression and conlbustion pressure
to drop much in the same manner as
bad rings and cylinder bores, only worse.
Pressure lost past a gasket goes into the
cooling system or an adjacent cylinder. If
it leaks into the cooling system, only one
cylinder will be affected, making if difficult
to detect the loss in power and gas
mileage.
A gasket blown or leaking between
cylinder bores affects two cylinders, consequently
power loss is easier to detect.
One thing is sure, if cylinder pressure is
getting into your cooling system, your
engine will eventually overheat. The
cooling system will be overpressurized
from cylinder pressures, forcing coolant
out of the radiator.
Burned Exhaust Valves-A burned exhaust
valve can't seal its combustion chamber.
Therefore, the cylinder with the bad valve
will produce less compression and power.
This occurs more often in emission-controlled
engines which operate at higher
temperatures for reduced emissions. The
valves run at higher temperatures and are
more susceptible to burning.
Worn Camshaft Lobes and Lifters-Worn
camshaft lobes and lifters almost always
occur together. This problem does not
affect an engine's oil consumption, but
really reduces its performance. The more
worn lobes, the more performance is
affected. Also, the metal particles being
circulated through an engine's oiling system
don't help any.
As a cam lobe and lifter wear, the lift
of the valve they operate becomes less. If
it is an intake valve, a smaller fuel charge
enters the combustion chamber, causing
reduced performance. The same thing
happens with the exhaust valve, but in a
roundabout way. If valve lift is reduced,
all exhaust gases cannot leave the combustion
chamber, consequently the new
fuel charge drawn in when the intake
valve opens will be diluted by exhaust
gases, reducing power output.
Carbon Deposits-Carbon deposits are not
a direct result of how many miles are on
an engine or its age, but are caused by
how the vehicle is used. A vehicle operated
on the open highway won't experience
excessive carbon buildup, assuming the
carburetion is near right. However, one
that is used for puttering around town at
30 MPH or so may develop the problem.
Carbon deposits don't require that an
engine be rebuilt to remedy the problem.
But, because its symptoms can fool you,
I'll discuss how carbon can affect an
engine, and how you can remedy the
problem.
Carbon buildup takes up room in the
combustion chamber, raising the compression
ratio. As a result, detorzatio~z
problems may develop, usually called
pinging or knocking. This is caused by the
fuel charge exploding from compression
rather than burning smoothly. Higher
loads are imposed on an engine by detonation,
and this can cause serious damage.
Damage can range from deformed mainbearing
caps to broken piston rings, and
even pistons. Detonation also blows head
gaskets. Preignition may also occur
when the carbon gets hot and acts like
a two-cycle model-airplane-engine glow
plug, igniting the fuel charge prematurely.
This potentially serious problem can melt
pistons, and break piston rings. Carbon
deposits also cause dieseling, or continuing
to run after the ignition is turned offsometimes
turning the crank in the opposite
direction.
Detonation, preignition and dieseling
don't necessarily hurt an engine's performance,
but the damage that can result,
particularly from detonation and preignition,
should concern you.
Carbon deposits hurt performance in a
couple of ways. Buildup around the valves
reduces flow to and from a combustion
chamber, thereby hurting power output.
And, pieces of carbon can break loose
and go out the exhaust harmlessly, or end
up on the piston top, between the exhaust
valve and its seat, or between the
spark-plug electrodes. Carbon on top of a
piston can reduce the clearance between
the piston and the head. The engine can
develop a knock, giving the impression
a rod bearing is bad when it isn't. I don't
know anything this can hurt except your
piece of mind.
Carbon between an exhaust valve and
seal prevents the valve from fully closing,
thus that cylinder won't be producing
fill1 power due to lost pressure. Also, on
the power stroke the hot file1 charge will
escape past the valve and seal, overheating
the valve with a good possibility of
burning it.
As for carbon between a spark plug's
electrodes, the plug will be shorted, preventing
it from igniting the fuel charge.
A misfiring cylinder results.
What usually causes carbon to break
off and create the troubles I've just discussed
is someone taking their car out
and "blowing the carbon out" or taking
advantage of an additive sale, then going