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

may be causing the problem at this pointa
leaky head gasket and/or a valve. If two
cylinders are down on pressure and they
are adjacent to one another, chances are
good the problem is a blown head gasket
between the cylinders. It could still be a
head gasket even if only one cylinder is
affected. A blown gasket is nearly always
accompanied by an unusual amount of
coolant loss from the radiator as cylinder
pressure will leak into the cooling system.
This situation is easy to diagnose. Remove
your radiator cap and look at the coolant
while your engine is running and warming
up. If cylinder pressure is escaping into it,
you'll see bubbles. Before making this
check, make sure your coolant level is up
to the mark. If you see bubbles, smell the
coolant. You should be able to detect
gasoline or exhaust fumes as the bubbles
surface and burst if they are caused by a
blown head gasket.
A sure way to test for this is to take
your car to a professional who has a
device which "sniffs" the coolant, It indicates
whether or not the bubbles are
cylinder gases and not just recirculating
air bubbles. If vou determine it is a bad
gasket, you'll have to remove a head to
replace it. Use the procedures outlined in
the engine teardown and assembly chapters
for this job. Check the head and block
surfaces for flatness. Fix any problems or
you may end up having to repeat the job.
Now for the valves. If you didn't find
your compression-loss problem with the
piston rings or a head gasket, the last
probable culprit will be a valve/s. There
are numerous reasons for valves leaking.
A valve may not be fully closing or it may
be burned. Both result in an unsealed
combustion chamber. If a fully closed
valve leaks, it's probably burned. So check
for full closure first. Unless the problem
is severe, you'll need vernier calipers or a
dial indicator.
Pull off the valve covers and locate the
cylinder you want-to check. It should be
on TDC (top dead center) just at the beginning
of its power stroke-not between
its exhaust and intake stroke. This ensures
both valves should be fully closed.
To do this, trace the spark-plug leads of
the cylinders you are going to check in
the distributor. Put a mark/s on the distributor
body in line with the terminals
on the distributor cap. Remove the cap.
When you crank your engine over and
line up the distributor rotor with the
mark on the distributor, you'll know the
cylinder will be reasonably near TDC on
its power stroke.
If both valves are fully closed, you
429CJ and SCJ VACUUM LEAK
Here's a problem that can frustrate the
best mechanic, and the solution can't
be found in any shop manual. The
problem is with the 429CJ and SCJ
end cylinders-numbers 1, 4, 5 and 8.
They won't fire at idle with the valve
covers removed, only when RPM is increased.
Chances are you won't run
into this problem if you have a CJ.
However, because SCJ's valves require
hot lashing, you obviously have to run
your engine without the valve covers.
It will idle rough with one off and
won't run at idle with both off! The
reason is the end, or corner cylinders,
fire in sequence-8, 1, 5,4-compounding
the problem. Four fire, then four
don't.
The cause of this problem is a vacuum
leak. I'll bet you think it has
something to do with the valve covers
being off You're right. The 429CJ/
SCJ intake ports are so large that the
end valve-cover bolt holes in the top
row are not blind like those in the
standard 4291460 head. They go
straight through into the number -1,
-4, -5, -8 intake ports as shown in the
photo on page 33. This creates a huge
vacuum leak when one of these bolts is
removed. The fuel charge is leaned so
much at low RPM that it won't fire.
Thread the bolts back in while the
engine is running-valve cover or nota'
and the cylinders start firing. So,
before running your 429CJ or SCJ
without its valve covers, thread the
bolts back in the holes immediately
above the end intake ports.
should be able to rotate the pushrods
with your fingers. It's unlikely the cam is
holding a valve open unless the valves
have been misadjusted. I know of no instances
where valve adjustment has gotten
tighter. If adjustment changes, it gets
looser. If the pushrod rotates, the rocker
arm has unloaded the valve, so it is free to
close. If it won't rotate, first check to
make sure that cylinder is at TDC, ready
to start the power stroke, then back off
on the adjustment using the procedure in
the engine assembly chapter.
Checking valve lift by measuring how much
a valve spring compresses from the fullopen
position to its closed position confirms
whether or not your cam is in good
shape. Refer to the chart when checking
your valves.
One thing to be aware of is your engine
probably does not have adjustable valves.
Rather, it will use positive-stop rocker-arm
studs or pedestal pivots unless your
engine is a 351C Boss, 351C HO, 429
SCJ or 429 CJ built before 10-18-69.
These engines had adjustable valves.
Otherwise your valves must be adjusted
using pushrods which vary k 0.060 in.
from the standard pushrod length. These
special pushrods should not be required
except during a jebuild when major machining
is done such as valve face and seat
grinding, or head and block resurfacing.
A word of caution, if your valve train
is the same as what was installed at the
factory it will have hydraulic lifters-unless
you have a 35 1 C Boss, HO or a 429
SCJ. Hydraulic lifters load the pushrods
slightly, making them a little hard to turn.
Therefore, don't let this fool you into
thinking the valve in question is open. If
your engine is equipped with a mechanical
cam, the pushrods will be loose. That's
why mechanical-cam engines are noisy.
They are loose because the required clearance,
or lash, is about 0.020 in. when hotas
opposed to the zero lash of hydraulic
lifters.
CHECKING VALVE LIFT
If all the valves appear to be closing as
just described, check the pushrods to see
if they are too loose. If one is, it could
mean a valve is hanging up in its guide,