by Jon Mikelonis
Introduction
Degreeing your cam. It's just one of those processes that
many hobbyists never want to perform. Why? Understandably,
the steps appear intimidating for a newbie and for others
the price of specialized tools will never justify their minimal
use. On top of that, being very involved in this hobby doesn't
require an individual to know how to build a motor. Sure,
you've got to be able to tune one, but the cleanest drawer
in your tool box may the one that holds the degree wheel and
dial indicator if you even have them. While a number of FordMuscle
readers have already built ten or more engines to date and
a greater number have swapped out twice as many cams, the
bulk of us MIGHT need to install a cam three times in our
entire lifetime. For these reasons, installing a camshaft
"straight-up", without even considering the purchase
of a degree wheel, is common practice today.
The "Straight-Up" Myth
...with the cam installed, fit your timing chain set so
that the "dot"' on the cam gear is at 6 o'clock
and the "o" icon on the crank gear is at 12 o'clock.
You are now done degreeing your cam, proceed with buttoning
up the timing chain cover, bolt on your accessories, say a
prayer, and fire your motor...
If it was only that easy. This scenario above describes installing
a cam at "crank gear zero" and it is not always
the optimum way to degree your cam. Curiously, the same procedure
is often times and incorrectly referred to as a "straight-up"
cam installation. More accurately described however, the term
"straight-up" refers to the intake and exhaust centerlines
being the same, not the "dot" and "o"
icon on the timing gears being directly opposed to one another.
In many cases but not all cases, setting the "dot"
and "o" icon on the cam gear and crank gear so that
they are inline CAN result in a "straight-up" install.
But be aware, cams ground with advance built-in, timing chain
gears machined with retard built-in, poorly marked timing
chain gears, and an accumulation of machine tolerances contribute
to the fact that "crank gear zero" and "straight-up"
ARE NOT the same thing. In fact, once your cam is set to "crank
gear zero" you may have to degree the cam to achieve
a "straight-up" install.
While even some cam manufacturers will suggest that degreeing
a cam is not always necessary, you'll be better off assuming
that it is mandatory. The procedure is a common sense verification
of any camshaft install. Ironically, we've recently determined
that no common sense was used when FordMuscle installed the
cam in our StreetWise
460. Here's a real-world example of the risk taken
when you assume "crank gear zero" and "straight-up"
are equivalent terms.
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| Carburetor adjustments and ignition
timing changes couldn't cure these sooty plugs. We suspected
the 460 had been degreed incorrectly. |
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Streetwise
460: Diagnosis
Fouled plugs, lack of power, hard restarts, and a roasting
intake manifold with normal water temperature. All of the
above were symptoms that lead us to believe that the cam in
our 460 had been degreed incorrectly. Specifically, we theorized
that it may have been installed retarded based on the symptoms
listed above. Retarding a cam is often performed to increase
top end power at the expense of low end torque. Not a good
condition for street use.
When a cam is
retarded too far, a number of problems will arise due to the
valve events all taking place too late. When an intake
valve opens too late, the initial amount of air and fuel
drawn into the chamber is reduced and exhaust gasses will
not be effectively purged from the chamber. When an exhaust
valve closes too late it can allow spent exhaust gases
to enter the intake port. This is also called reversion. Rather
than going into a complete explanation of cylinder pressure,
scavenging, and reversion, let's just crack open this big
block Ford and see what the heck is going on.
Visual Inspection
The first order of business
was to tear down the front- end of our motor in order to gain
access to the timing chain gears. The intention was to inspect
the alignment of the timing marks on both gears and to compare
the intake centerline to the cam card for the Comp Cams XE274-10.
All Comp camshafts are ground with 4 degrees of advance. Therefore,
since the cam card specified a lobe separation of 110 degrees
and the specs written assuming a 106 degree intake centerline,
having the timing chain gears to "crank gear zero"
should have produced the desired result.
Using the crankshaft sprocket shown in the sidebar, we
rotated the crank clockwise with a breaker bar and 1/2"
drive to find Top Dead Center (TDC) of the number one
piston's compression stroke. |
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At TDC of the compression stroke, the "dot"
punched on the camshaft gear and the "o" icon
on the crankshaft gear were a half-tooth from being directly
opposed. For effect, the markings are emphasized in red.
Based on the misalignment shown, there seemed to be a
problem. |
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Before breaking out the cam degreeing tools, we tried
moving the cam gear over a tooth. Again, we still still
could not get these marks to align properly. We verified
that we had an early 429/460 timing chain set with "Factory
Top Dead Center" timing. We'll discuss the two common
385-series timing chain sets in a later section of this
article. |
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We set the timing chain back to the same position as shown
in caption 2. Next, we got prepared to find absolute TDC
in order to verify the intake centerline of our problem
motor. |
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 (Finding
Top Dead Center and Determining Intake Centerline) |
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In This Article...
Even if you're installing an off-the-shelf camshaft,
we'll show you how important it is to verify
intake centerline. This article explains the
difference between setting your timing gears
to "crank gear zero" and installing
a cam "straight-up". We'll then demonstrate
the pitfalls with a real-world example using
FordMuscle's Streetwise 460. |
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a
cam and this combination crankshaft socket and adjustable
degree wheel mount will help eliminate any errors during
the procedure.
