Degreeing your Cams

Last Updated September 13th, 2004

The first question most people will ask when they see this page is, "Why would I want to degree my cam?"  The answer is that most people wouldn't.  However if you decided to build adjustable cam sprockets, you would do this in order to determine how your adjustments have affected the valve timing.  You might also do this if you want to see how close the factory tolerances are to where the numbers are supposed to be. 

For what it's worth, one tooth on the timing belt is worth about 9 degrees of cam rotation and 18 degrees of crank rotation.  Based on computer simulations, a mere retard of 4 crank degrees will boost power by 6hp at redline with a minimal expense of low end torque.  An advance of 4 degrees will cost 11hp at redline but boost low end torque a little.  So for those who want to fine tune their engines, this is a subject worth understanding.


Difficulty:    

Time Investment:  Under 2 Hours
This is assuming you are already doing the timing belt, already have everything apart, and have already come up with a mechansim to support the dial gauge.


Go to Pictures

Go to Theory

General Points to Understand
Chrysler Stock 3.0 Valve Timing
Calculating Where the Centerline Should be

Go to Instructions

Prepare the Engine
Modify the Dial Gauge Mounting Bracket
Degree the Crank
Degree the Rear Cam
Degree the Front Cam

Go to Tools & Supplies

Go to Notes




Pictures:

Click on a picture to enlarge it

There is the Comp Cams Degree Kit in the Box.
These are the goodies inside the box.  There is also a VHS tape describing what to do with the kit - on a small bock chevy (pushrod).
This is a piston stop.  It screws into the spark plug hole and stops the piston at an exact point prior to TDC.
This is a degree wheel.  In this picture it is installed as shown in the video.  This is the difficult way to do it.
Building up the center with a little electrical tape, the degree wheel will slide over the crank bolt.  This is much MUCH easier to work with.
Here's a shot of the installed degree wheel.  Note the piece of wire (included in the kit) attached as a pointer for the wheel.
This is a shot of the dial gauge and mounting bracket that come with the kit.  The easiest way to make this work is to cut the threaded part off the bottom and weld a bolt in its place that can screw into the valve cover hole.
Prior to taking measurements, the gauge should be zeroed at max lift.  Tests are performed on cylinder #1 in the rear bank and cylinder #4 on the front bank.
Measurements can be taken at various markings on the gauge and averaged.  30/1000ths, 40/1000ths, 50/1000ths, etc...


Theory, Numbers, Concepts, etc:

General Points to Understand

Discussing cam retard and advance can get a little tricky when you start thinking about crank degrees vs. cam degrees and when you think about the relative rotation of the cam sprocket with respect to the cam.  When working with these things, keep the following points in mind:

Chrysler Stock 3.0 Valve Timing


On the earlier Chrysler applications, `87, `88, and `89, the valve timing is as follows:

               IVO (Intake Valve Opens) 19 BTDC (Before Top Dead Center)
               IVC (Intake Valve Closes) 57 ABDC (After Bottom Dead Center)
               EVO (Exhaust Valve Opens) 57 BBDC (Before Bottom Dead Center)
               EVC (Exhaust Valve Closes) 19 ATDC (After Top Dead Center)

Mapped out on a chart showing all 720 degrees of crank rotation for one 4 stroke cycle this valve timing looks like the following.  In this case, the centerline of the intake lobe should come 109 degrees after TDC.



On the later Chrysler applications, the valve timing is as follows:
 
               IVO (Intake Valve Opens) 19 BTDC (Before Top Dead Center)
               IVC (Intake Valve Closes)
59 ABDC (After Bottom Dead Center)
               EVO (Exhaust Valve Opens)
59 BBDC (Before Bottom Dead Center)
               EVC (Exhaust Valve Closes) 19 ATDC (After Top Dead Center)

Mapped out on a chart showing all 720 degrees of crank rotation for one 4 stroke cycle this valve timing looks like the following.  In this case, the centerline of the intake lobe should come 110 degrees after TDC.



Calculating Where the Centerline Should be

A custom cam should come with the centerline specification on the card.  In order to calculate the centerline angle for another cam based on known valve timings, do the following, looking at the intake valve.

For the intake valve timing opening at 19 BTDC and closing at 59 ABDC, consider TDC = 0 degrees.

Then calculate the total duration or time the valve spends open in degrees of crank rotation.
(19 degrees before TDC) + (TDC to BDC = 180 degrees of rotation) + (59 degrees after BDC)
19 + 180 + 59 = 258 degrees of duration.

The center of the lobe will occur halfway through that duration.  258
÷ 2 = 129 degrees.

Since we know the valve start to open 19 degrees before TDC and the center line falls 129 degrees, we can subtract 19 from 129 to get the crank position after TDC.  129 - 19 = 110. 


Instructions:

Prepare the Engine
This procedure is best done in conjuction with changing the timing belt.  If you do this, you'll have easy access to all of the parts and will be able to see all of the timing marks.  If your timing is already set, you will still have to remove the crank pulley and the timing cover to do this although is may be possible to disassemble fewer components than you would if you actually removed the timing belt.  It also may not be possible to pull this off.  The following assumes you've already removed everything down to the timing cover and that you have a belt on the sprockets.

1.  Remove the upper plenum at the least, in order to better see what you're doing.  The lower plenum can probably remain in place.
2.  Remove the valve covers.
3.  Remove all of the spark plugs/wires.


Modify the Dial Gauge Mounting Bracket
The dial gauge mounting bracket is designed to screw into a little hole that doesn't match anything on our engine.  One way to modify it is to cut that threaded part off and weld on a bolt that will screw into the valve cover bolt holes.  You could also build your own bracket or rig up a set of clamps to hold things into place.  This is probably the most difficult part of the whole operation.


Degree the Crank
1.  Install the degree wheel over top of the crank bolt as shown.
If you try to hold it on with the crank bolt, you will encounter a new meaning to the word "frustration".  Since the wheel must be adjusted at fixed crank positions, you have to be able to move it without moving the crank.  If the bolt is tight enough for you to turn the crank in the forward direction, it won't come back out without rotating the crank sligthly in the reverse direction.  Thus, your meansurements will already be inacurate.  Instead, tape up the middle of the wheel as shown and slide it on top of the crank bolt.

2.  Install the wire pointer using an available bolt and bolt hole. 
The goal here is to get the pointer to stay in a fixed postion on the outside of the wheel and for it to be in a place that you can easily see it.  You can use one of the PS Pump bolts in one of the holes on the front of the side of the engine.

3.  Install the piston stop in spark plug hole #1.
Rotate the crank so that the cam sprocket is about 1/4 rotation from the timing mark.  Fully extend the stop.  Then screw it into the spark plug hole.

4.  Gently rotate the crank forward until you  hit the piston stop. 
It may tighten up at points, but you'll know when you hit the stop because it will stop cold.

5.  Rotate the degree wheel so that the pointer points at 0/360 degrees TDC.

6.  Gently rotate the crank backwards until you hit the stop.

7.  Rotate the degree wheel to the point half way between the current reading and zero.
Thus if the second reading was 62, rotate the wheel to 31 degrees.  Your crank is now dead on with 0/360 at TDC for cylinders #1 and #4.

8.  Remove the piston stop.

9.  Do a reailty check by rotating the crank until the wheel points to zero. 
Do the timing marks line up?  If so, it worked.  If it's more than a fraction of a tooth off it didn't work.  Try again.


Degree the Rear Cam
1.  Set up your dial gauge so that the tip of it rides the top of the rocker directly over the end of the #1 intake valve stem.
As you rotate the crank, the cam will turn.  As the cam turns, the rocker will move up and down.  At full lift, the end of the dial gauge should be right up next to the corner of the rocker.  It shoudn't, however, go over that corner.  At zero lift, it should slide backwards on the flat part of the rocker.  At no point should there be any gap between the end of the dial gauge and the rocker.  The dial gauge should be oriented as parallel to the valve stem as possible.  Finding the optimum position will take a few tries.

2.  Rotate the crank until the #1 intake valve is at max lift.  It will sit at max lift for an extended period. 
Depending on exactly what you did in the previous step, there could be a little upward bobble right before the valve goes down.  If so, you can ignore that point.  Max lift is steady point you see for a good duration when looking at the dial.

3.  Zero the dial gauge.
Rotate the outer ring on the dial gauge to zero.  Then rotate the crank 4 times around so that the valve goes up a couple times and stop at max lift.  If the gauge is still on zero, you're good to go.  If not, it moved slightly.  Rezero the gauge, re-rotate, and repeat until it stays at zero.

4.  Take the forward measurement at 0.050".
Rotate the crank in the forward direction until you see the dial dip to 0.050".
If you go past that mark, you can reverse the engine rotation, go back past the mark, and then come at it again from the forward direction.  You want to do this to ensure that there is no slack in the timing belt.  When you hit dead on the mark, read the degree wheel and write down the number.  For a reality check, this should read something like 8 - 15 degrees.

5.  Take the reverse meansurement at 0.050".
Rotate the crank backwards past max lift, and continue rotating until the dial goes down 1/2 to 3/4 a turn past 0.050".  Then come back slowly to the 0.050" mark.  Every time you take a measurement, the crank should be rotating in the forward direction.  When it's dead on, write down the number on the degree wheel.

6.  Repeat the last 2 steps at the 0.040", 0.030", and 0.020" markings on the degree wheel.
Note that these markings denote "negative lift" from the point of max lift, not the absolute lift of the cam lobe.  The goal is to mark out specific points in each direction of the max lift in order to determine the true cam centerline.  The cam centerline is essentially the middle of the max lift area on the lobe. 

This drawing represents the shape of a cam lobe with lines marking two of the measurement points you will check. As you turn the crank and watch the dial, you'll see that the profile you are meansuring feels more like this than a rounded lobe.  The valve quickly lifts up, max lift is maintained for a long duration, and then the valve quickly goes down.

 

When you are done measuring, your results will look something like the following:

Gauge Marking
Low Num
High Num
0.050"
8
208.5
0.040"
11
206.5
0.030"
13.5
204.5
0.020"
16
202
 

7.  Now you can determine the cam centerline or the average midpoint of the measurements.


For each set of measurements, do the following:
          L = Low Measurement
          H = High Measurement

          Centerline = ( (H - L) ÷ 2 ) + L

For the numbers above that would be:
          ( (208.5 - 8) ÷ 2 ) + 8
          ( 200.5) ÷ 2 ) + 8
          ( 100.25 ) + 8
          108.25


Gauge Marking
Low Num
High Num
Center Line
0.050"
8
208.5
108.25
0.040"
11
206.5
108.75
0.030"
13.5
204.5
108.75
0.020"
16
202
109.00
Average:
108.69

The consistency of the centerline numbers will tell you how good of a job you did taking measurements.  They should deviate very little if you were careful.  If the numbers are wide spread, re-measure.  You may have read the degree wheel wrong.  Once you've got some good results, average them to get your final number.  In this case, it came out 108.69 degrees.

The true centerline for the `90+ 3.0 cam is 110 degrees.  If the number based on your measurements is higher, the cam is retarded (center comes later with respect to TDC).  If the number is lower, the cam is advanced (center comes earlier with respect to TDC).


Degree the Front Cam
Follow the exact same procedure used for the rear cam on the front cam using cylinder #4.  All of the calculations are identical and you don't have to account for a change in angle because cylinders #1 and #4 are exactly 360 degrees apart with respect to their valve events.


Tools & Supplies:


Notes: