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Cam Degreeing KZ twin cam motors
Understanding advance vs retard
The best way to grasp this is by looking at your engine with the cams installed from the ignition side. Looking at #4 cylinder’s cam lobes.
The crank spins clockwise. The cams spin clockwise and at half the speed of the crankshaft. This is important to understand. You turn the crank 720 degrees [two revolutions] to make the cams turn 360 degrees [one revolution].
You phase the cam by turning the crankshaft CW or CCW.
If you wanted to advance either cam and could physically grab the lobe and turn it with your fingers, you would turn the lobe clockwise, opening the valve earlier in the intake cycle. There is no easy way to to do that.
Instead, you turn the crank counter clockwise, tighten the sprocket bolt, then turn the engine over & check your open and close numbers again, then calculate your new lobe center value.
(big number - small number) + 180 / 2 = “lobe center value”)
If you wanted to retard either cam, you would turn the crankshaft clockwise, tighten the sprocket bolt, then turn the engine over & check your open and close numbers again, then calculate your new lobe center value.
Understanding Lobe Center Value Relationships
If you had both cams on 104 lobe centers and wanted to advance both cams 2 degrees you would end up with a 102 Intake Lobe Center and a 106 exhaust lobe center.
Using the open / close numbers in the example
Current values for 104 lobe centers:
IVO 25 BTDC
IVC 53 ABDC
EVO 53 BBDC
EVC 25 ATDC
Advancing the Intake cam 2 degrees yields a timing of:
IVO 27 BTDC
IVC 51 ABDC
(51 - 27 )+ 180 / 2 = 102 Intake Lobe Center
Advancing the Exhaust cam 2 degrees yields a timing of:
EVO 55 BBDC
EVC 23 ATDC
(55 - 23)+ 180 / 2 = 106 Exhaust Lobe Center
I wanted to point this out because it confuses people sometimes. Here’s a basic rule to remember.
Advancing the Intake Cam yields a lower numerical lobe center value while Advancing the Exhaust Cam yields a higher numerical value.
A good way to visually check things if you are having doubts about your accuracy is the relevant position of the lobes to the valve cover surface with the piston at TDC.
In this above photo you can see the intake cam is timed late [retarded].
If the cams are installed straight up [same lobe center value] the lobes will be split equally by the valve cover surface.
It’s much easier to degree the cams when you use light springs. After you’re done, pull the head off and assemble it with your running components.
You can check timing at running lash if you prefer instead of zero lash.
If you don’t have a cam card for your cams, pick a checking lift and follow the process outlined here. The checking lift isn’t all that important, it’s just a relative point to use for calculating the centers. It’s better to use something greater than .020” lift because it gets you up away from the opening ramp and more onto the lobe.
As mentioned before, using a shim on top retainer and bucket gives you a handy place to position the indicator tip so that it doesn’t walk on the shim.
You probably find that the cams you have don’t exactly match what the cam card says. Don’t worry about it unless it’s way off. In that case you really need to be looking at what you’re either doing wrong or the cam itself.
It’s generally best to turn the engine over using the opposite end of the crankshaft instead of the end the degree wheel is mounted on.
Pay attention that you don’t bump the pointer for the degree wheel.
While you have the degree wheel & indicator setup with light springs, you can use them to help check contact points through the overlap lift range. It’s much clearer to see what’s going on with the dial indicator than with clay.
You’re likely going to find that the closest point of contact for the intake valve occurs a few degrees ATDC, usually around 5 - 8 degrees.
Timing values that increase overlap lift will tend to make more upper RPM power at the cost of some bottom and middle.
Advancing both cams can help put bottom end in the motor.
Unlike a V8 automotive cam where the Lobe Separation Angle is fixed, you have total adjustability of it with Dual Overhead Cams. Each cams timing is independent of the other. Changes in one cam’s timing will alter the Lobe Separation Angle which in turn alters the characteristics of the engine in terms of Peak HP , Peak Torque and the RPM they occur at.
Tools & Parts Required:
Slotted Camshaft Sprockets - Buy them or slot your own.
Positive Stop -Screws into spark plug hole. The purpose is to stop the piston travel at the same location when turning the crankshaft clockwise & counter clockwise. Buy one or make one from an old spark plug, long 6mm bolt & nut.
Degree Wheel - Self explanatory
Dial Indicator - 1 inch travel indicator with a long skinny tip. It has to fit into a narrow spot and travel without dragging or being bumped by the cam lobe.
Pointer - An old wire coat hanger will suffice. You want it secured well.
Here’s the setup I use. Click the pics to enlarge them.
The dial indicator setup is crucial. It simply cannot move around on you and the tip must travel unhindered through the full lift range of the cam and return to zero every time.
It’s easier to do this with valves in only one cylinder and using light springs. Another tip is to use a shim on top retainer with a shim on top bucket. Position the shim removal notch in a position that allows the indicator tip to rest in it. It will prevent it from walking.
Finding True TDC Using a Positive Stop
Do this with the head installed but the cams are not yet installed.
The degree wheel should be installed with a fixed pointer. Use the factory T mark for 1&4 to find your initial TDC and set the degree wheel pointer to TDC on your degree wheel.
Turn the crankshaft CCW so that #4 piston is about 1/3 of the way down in the bore.
Set the stop bolt so that it protrudes about ¼ inch past the threaded body into the combustion chamber & thread the stop into the #4 spark plug hole.
Slowly screw the stop bolt down in about another 1/inch. GO EASY. If you feel resistance, stop and back the stop bolt out a little.
Rotate the crank clockwise gently bringing the piston to rest against the stop bolt. Read the number indicated on the Degree Wheel by the pointer. Let’s for the sake of expression say it was 60. Write down the number.
Rotate the crank CW until the piston again gently touches the stop. Again, write down the number. For expression, let’s say it was 66.
TDC is half way in between those two values of 60 & 66. You have 6 degrees difference. Half of that is 3 degrees. Move your pointer 3 degrees to 63. Repeat the CW / CCW rotations to verify you have the same number reading in both directions. When you do, you can remove the positive stop. When you rotate the crankshaft to TDC using the Degree wheel, it will be true TDC,
Setup The Dial Indicator
Getting the correct angle and finding the spot where the tip sets correctly is tricky. You will have to fiddle with it until you find that spot. I personally like to use a very skinny, long tip on my dial indicator. Also I’ve found it very helpful to use a shim on top bucket. Those buckets have the little notch for prying out the shims. That notch works perfectly to keep the tip from walking around. That happens when it rests on the shim.
Use a shim that gets you as close to zero lash as you can get.
Setup your dial indicator with enough pre-load on the tip so that it will read the full travel of the valve lift. Make sure it’s not bottomed out.
Position the cam so that it’s pushing the valve full open & adjust the angle of the indicator as best you can to get the tip in the perfect spot.
Turn the crankshaft CW and watch the indicator. When the valve is fully closed, set the indicator outside dial to read zero. Turn the crankshaft CW, slowly, going through the full lift cycle of the valve. When the valve closes fully, the indicator should read zero. If it doesn’t, keep fiddling with it’s positioning until it does return to zero.
Turn the engine over a few more times to verify the indicator returns to zero. When it does that repeatedly, you are ready to degree the cams.
Degreeing The Cams
With a checking lift value of .030” and intake timing of IVO 25 BTDC / IVC 53 ABDC. Watching your dial indicator you would note the degree wheel reading when the intake valve was open .030”, continue rotating through the cycle and as the valve is closing, again note the degree wheel reading when the valve is .030” from closing to rest on the valve seat. There are 3 possible results. Dead on, advanced or retarded. [early = advanced - late = retarded]
Those two values are used in calculating the lobe center value (big number - small number )+ 180 / 2 = “lobe center value”
You just repeat the above process until you get the correct numbers. It’s always the same process. It doesn’t matter which cam it is. Just remember to keep in mind that the Lobe Center Value is always derived from the open / close numbers and that you move the crank in the opposite direction of where you want the cam’s timing to be. Back the crank up to Advance. Move the crank forward to retard. That and the relative concept that Lobe Center Values go lower when advancing the intake cam and go higher when advancing the Exhaust Cam.
The process of degreeing the cams isn’t nearly as complicated as it may seem. There are some basic principles to understand and some processes to follow in specific order. A few special tools are required and some basic math to apply.
Truly, the most difficult part of the process is setting up the dial indicator so that it repeats. It’s a tight fit that the indicator tip must travel in. If the tip drags or gets bumped by the cam lobe, your opening and closing numbers will keep changing on you. In return you’ll get frustrated.
We are going to use the following valve timing values throughout this article. Intake timing of 25/53. Exhaust timing of 53/25. Those values are at a checking lift of .030 inch. Those opening and closing values calculate to 104 lobe centers. You’ll see the relevance as you read on.
Order of Progression
The checking lift is a predetermined amount the valve is opened when you read your opening & closing numbers. It can be any value you choose. It’s often .050” , .040” or .030”. The cam card will have the manufacturers suggested checking lift listed.
So with a checking lift value of .030” and intake timing of IVO 25 BTDC / IVC 53 ABDC. Watching your dial indicator you would note the degree wheel reading when the intake valve was open .030”, continue rotating through the cycle and as the valve is closing, again note the degree wheel reading when the valve is .030” from closing to rest on the valve seat. There are 3 possible results. Dead on, advanced or retarded. [early = advanced - late = retarded]
Those two values are used in calculating the lobe center value (big number - small number) + 180 / 2 = “lobe center value”
It’s important to not string the math functions together on your calculator or you’ll get an incorrect lobe center value. Break the functions down: (Big Number - Small Number )= X (X + 180 /2) = lobe center value.