Therefore, when you attempt to locate the middle (or centerline) of the asymmetrical lobe there is an automatic error. It could be as little as 2° or as much as 6° depending on the actual lobe design. Since the opening and closing at .050 lift method is not affected by the lobe design, it is more accurate to degree this way. This method will also verify your actual duration figures. To understand cam timing specifications, you must first understand the difference between intake and exhaust centerline and lobe centerline (which should be more understandably stated as lobe separation). Lobe centerline (or separation) is the distance in cam degrees between the maximum lift point (centerline) of the intake lobe and the maximum lift point (centerline) of the exhaust lobe.
This separation is ground in the cam and cant be changed unless the cam is reground. Intake and exhaust centerline relates to the phasing (timing) of the cam to the crankshaft.
To locate the intake or exhaust centerline you must find maximum lift of that lobe. As in finding TDC, you must begin by using an arbitrary figure, such as thousandths of an inch instead of degrees, say .050. With the dial indicator on the intake lifter, rotate the engine in the normal direction until you reach maximum lift. This is where the dial indicator changes direction. At this point set the dial indicator at zero.
Back the engine up until the dial indicator reads .100. Turn the engine back in the normal direction of rotation until the dial indicator reads .050. At this point, record the degree number that the pointer is on.
Continue to rotate in the normal direction of rotation until the dial indicator goes past zero to .050 on the other side of maximum lift. Record the degree number that the pointer is on. Add the two degree numbers together and divide by two.
That number will be the location of the maximum lift point of the intake
lobe in relation to the
crankshaft. As you can see, this method does not tell you anything about the cam, or how accurately it is made.
A detailed proceedure from Lunati Cams for SYMETRICAL
cam lobes ONLY
The following is the method of degreeing a
cam which Lunati Cams recommends. The first step in
degreeing a cam is to obtain a few items which should be a part of every serious engine builders
tool chest. These items are:
1. A large Degree Wheel
2. A 1" Dial Indicator & Magnetic Base Stand,
3. A steel Deck Strap Kit
All of the above are available as LUNATI CAMS DEGREE WHEEL KIT, PART NO. 80001
We suggest that the engine be torn down to
expose the tappets. A more precise degree reading will
result if it is taken from the tappet area rather than from the valve retainers. To accomplish this
one has to disassemble the engine to expose this area. Rocker arm geometry can alter the readings
on your cam. Valve springs can deflect the cam enough to give false readings. Rocker arm
mounting studs that are not consistently straight will greatly alter your cam readings. We suggest
that all these components be bypassed to insure a true reading.
To begin the actual degreeing procedure, the
degree wheel should be secured to the crankshaft;
preferable the front end. A pointer of some type such as a piece of wire should be secured to the
front of the engine. The engine should be capable of turning in either direction. Rotate the
crankshaft until the number one piston is at approximate Top Dead Center and align the pointer
with TDC on the degree wheel.
The next step is to find true Top Dead Center
(TDC). One method of doing this is to secure a flat
strap (1 1/2 x 1) that will bridge the bore (with the heads removed). Drill and tap a 3/8" hole in the
center strap and insert a bolt so it will protrude down into the bore about 1/4 to 1/2 inch. The bolt
will contact the piston, thus stopping the piston movement. A steel Deck Strap Kit is included in
the Lunati Degree Wheel Kit, or is available separately (part number 80013). At this point you
should mark the degree wheel. Now rotate the engine in the opposite direction until the piston
stops. Make another mark on the degree wheel. If the degree wheel is properly located, there will
be an equal number of degrees on both sides of the mark. If an unequal number of degrees exists,
the degree wheel will have to be relocated. For example, if you come up with 34 deg. on one side
and 30 deg. on the other side, the wheel will have to be moved 2 deg. to compensate for the
misalignment. After the wheel has been relocated, the same amount of degrees should exist on
both sides of the markings.
If the heads are on the engine, another method
of finding TDC is necessary. This method uses an
old, discarded sparkplug. Remove the porcelain and use a tap, 3/8" 24NF, to cut threads through
the plug. Insert a Bolt so that it will protrude through the plug approximately one inch. Remove
rocker arms and pushrods so valves will not be bent. Repeat same operation as with the first
The next step is to install your new camshaft
and line up the stock timing marks. Use a mechanical
lifter for flat tappet grinds and a roller tappet if the cam is a roller grind. The indicator must be
positioned securely above the lifter. The stem from the dial indicator should be aligned with the
lifter as close as possible. Misalignment will cause an improper reading. Install the lifter in the lifter
bore of the number one intake. Now that the dial indicator is secured to the block in line with lifter
travel, rotate the engine at least two revolutions. Make sure the dial indicator is working freely and
the lifter is not sticking or binding in the bore.
Rotate the engine clockwise until maximum lift
is reached. Zero the dial indicator and continue in
clockwise rotation until a .050 reading is reached. Mark the degree wheel at this time. Rotate the
engine counterclockwise until maximum lift is reached again. Continue counter clockwise rotation
until a reading of .070 is indicated. Now rotate the engine clockwise until the .050 is indicated on
the dial indicator. This operation will take up any slack that exist in the timing chain and gears.
Halfway between these two marks is the center on the intake lobe. An example of this might be
153" on one side of the approximate centerline and 63 deg. on the other side. By adding these two
figures you get a sum of 216 deg. This number halved gives 108 deg. This is your lobe center. If
your cam is ground on 108 deg. lobe center line, then the cam is installed at split overlap or straight
up. If the number is smaller such as 106 deg., then the cam is two degrees advanced. If the lobe
center comes up as 110 deg., then the cam is two degrees retarded. Adjustments should be made
with the use of degree bushings, offset keyways or a compensating crankgear.
Once you learn this method of degreeing a cam,
you won't use any other method. This is the most
accurate method of installing a cam. Good Luck!
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