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

used, but good cam and its lifters in an
engine other than the one in which they
were originally installed. The lifter bore
centers will not be in the same exact
relationship to the cam lobes as in its
original engine. So this is similar to
mixing up the lifters.
Almost without exception, the rules
realted to proper cam and lifter combinations
and installation methods have to
do with avoiding excessively high contact
pressure between cam lobes and lifters.
Loads exerted between a cam and its
lifters during normal operating conditions
are extremely high. Consequently,
if there's any wrong move with the choice
of cam components and their installation
between now and the first 30 minutes of
engine operation, the chances of a carnshaft
and its lifters being ruined are very
high. It's important to adhere to proper
procedures when choosing and installing
your camshaft.
Camshaft Lobe and Lifter Design-For a
clear understanding of why certain things
have to be done when dealing with your
engine's camshaft and lifters, a quick
lesson in cam lobe and lifter design is in
order. First is the profile of a lobe, or
what one looks like when viewed from
the cam end. A cam's profile governs
how far its valves open in addition to
when they open and close. This is an
oversimplification, but it's OK for our
purposes.
When a valve is closed, the lifter is on
the base circle of the cam lobe described
by a radius. When the lifter is on the highest
point of the lobe, it's on the toe of
the lobe and the valve is fully open. Be-
tween the base circle and the toe are the
opening and closing ramps. Sketch on
page 63 shows the difference between the
base-circle diameter and the distance
from the toe directly across the camshaft
centerline to the base circle is cam lift at
the lifter-not the valve.
During the camshaft manufacturing
process, lobe surfaces are not ground
parallel to the camshaft centerline, but
are ground at a rake angle-lo in most
instances. Also, the lifter foot that contacts
the cam is not ground flat, but has
a spherical radius, or is ground convex.
Ford uses a 30-inch radius. At first this
sounds odd because one would think
pressure between the lobe and lifter
would go up as area between the two is
reduced. However, this machining ensures
a reasonable and predictable contact
pressure within practical machining tolerances.
The lifter-foot radius and lobe
angle guarantee good cam-to-lifter contact
area for consistent camshaft and
lifter life.
The way camshafts and lifters are
machined serves another important function.
Cam-lobe contact is made off-center
rather than directly on the lobe's center.
Consequently, the lifter rotates to minimize
wear of the two components and to
ensure good lifter and bore lubrication.
CAM & LIFTER INSPECTION
During their operating life, a cam and
its lifters wear gradually. How much de"-
pends on how an engine is operated and,
more importantly, how it is maintained.
You must determine whether yours has
worn so badly that it shouldn't be used.
Difference between these two measurements gives you camshaft lobe lift. It should
measure approximately 0.230 inch-0.0290 inch depending on which engine you have.
This method is not accurate for determing high-performance cam lift. Ramp area of a longduration
cam extends farther around the base circle, resulting in a larger-than-actual
base-circle-diameter reading, or a less-than-actual lobe lift. Chart on page 10 lists lobe
lifts.
I'll say it right now. Using an old camshaft
and lifters in a newly rebuilt engine
is a risky deal. It's not uncommon for a
new cam to fail during its first 100 milesor
even before it gets out of the driveway.
Finally, if you've lost track of the
order of your lifters, toss them away and
get new ones. I recommend going the full
route and getting a new cam too because
the lifters are the expensive part. The
odds of getting 16 lifters back in the right
order on 16 cam lobes are absolutely
astronomical: 20,922,789,980 to 1.
Check the Camshaft First-When checking
your cam and lifters, check the cam first
because if it's bad you'll have to replace
the cam and the lifters, regardless of
lifter condition. Remember the second
rule: never install used lifters on a new
cam.
The first thing you do is get out your
trusty micrometers-vernier calipers are
OK-and check your cam's lobe lift. Maybe
you did this during the diagnosis process
prior to removing and tearing down
your engine. You'll have used a dial indicator
at the end of a pushrod to check
the lobe lift the rocker arm sees, or
actual lobe lift. If you used this method
and made a determination about your
cam, you can forget measuring the
lobes directly because lift measured at
the lifter or pushrod is accurate. On the
other hand, using verniers or mikes becomes
increasingly inaccurate with highlift,
high-performance camshafts because
the ramp area extends farther around the
lobe and reduces the length of the base
circle.
After arriving at a figure for each lobe,
compare all the exhaust-lobe figures. If
the numbers aren't within 0.005 inch you
know some lobes are worn excessively
and the cam should be replaced. Lobe
positions for intake and exhaust valves,
from either end of the camshaft are:
IEEIIEEIIEEIIEEI.
Another thing to note is the wear pattern
on each lobe, particularly at the toe.
If the wear has extended from one side of
the toe to the other and well down onto
the ramp area, the cam has seen its better
days and should be replaced, even though
its lift checks OK. This goes for pitting
too. Any pitting on a lobe's lift areas
indicates metal loss which will probably
show up on its mating lifter. A "fullwidth"
wear pattern or pitting of a cam's
lobes indicates the cam and lifters should
be replaced.
Cam-bearing journals are "bullet
proof '-they never seem to wear out-at
least I've never seen any worn out. However,
if you feel compelled to check yours