How-To: Degreeing a Cam
10-28-2006, 01:44 PM
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How-To: Degreeing a Cam
I recently purchased the Cam Degreeing Kit SUM-G1056 from Summit, and am posting the How-To here so you can save some $ instead of spending the $80 for the kit like I did. You can take a trip to Harbor Freight or wherever and get all these parts for about half of what the kit sells for. Also, this How-To is with the CYLINDER HEADS ON THE BLOCK.
Okay, let's get started.
Parts List
2 low tension checking springs
1 wire pointer
1 TDC stop (head on engine type)
1 11" degree wheel
3 adapter bushings
1 flat washer
1 0-1" dial indicator
1 stand with magnetic base
Why Should I Degree my Camshaft?
Valve opening and closing points are what give an engine a specific performance curve. Degreeing a cam is the only way of finding out where your valves are opening and closing in relation to the crankshaft position. By degreeing the cam, you will be able to detect and compensate for errors in valve timing. These errors can be due to variations in the machining of the timing set, the crank keyway position, or the cam itself.
Getting Started
There are two basic methods of degreeing camshafts. One locates the theoretical centerline of the #1 intake lobe. The other locates the opening and closing points of the #1 intake valve (or lifter) at a specified amount of lift - usually .050". We are going to use a combination of both and adjust the intake centerline (if needed) to make sure the opening and closing points are where they should be.
Most modern cam lobes are asymmetrical by design so relying on theoretical centerline position alone is not good enough. Relying on centerline alone will also miss a love that is either too big or too small. In other words, centerline tells you nothing about any variation of the opening and closing ramps of the lobe. Depending on the amount of variation, you can either split the difference or set either the intake opening or closing point as it specified position. Keep in mind the point at which the intake valve closes has an obvious effect on cylinder pressure.
Okay, let's get started.
Parts List
2 low tension checking springs
1 wire pointer
1 TDC stop (head on engine type)
1 11" degree wheel
3 adapter bushings
1 flat washer
1 0-1" dial indicator
1 stand with magnetic base
Why Should I Degree my Camshaft?
Valve opening and closing points are what give an engine a specific performance curve. Degreeing a cam is the only way of finding out where your valves are opening and closing in relation to the crankshaft position. By degreeing the cam, you will be able to detect and compensate for errors in valve timing. These errors can be due to variations in the machining of the timing set, the crank keyway position, or the cam itself.
Getting Started
There are two basic methods of degreeing camshafts. One locates the theoretical centerline of the #1 intake lobe. The other locates the opening and closing points of the #1 intake valve (or lifter) at a specified amount of lift - usually .050". We are going to use a combination of both and adjust the intake centerline (if needed) to make sure the opening and closing points are where they should be.
Most modern cam lobes are asymmetrical by design so relying on theoretical centerline position alone is not good enough. Relying on centerline alone will also miss a love that is either too big or too small. In other words, centerline tells you nothing about any variation of the opening and closing ramps of the lobe. Depending on the amount of variation, you can either split the difference or set either the intake opening or closing point as it specified position. Keep in mind the point at which the intake valve closes has an obvious effect on cylinder pressure.
10-28-2006, 01:53 PM
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NOTE: References to clockwise and counterclockwise are based on a person facing the front of the engine.
1.) Install the checking springs on the #1 cylinder. If you don't wish to remove the existing valve springs, you can degree the cam directly off a solid lifter. Make sure the specs on the cam card are taken from the lifter also. If they are taken at the valve, divide the valve lift by the specified rocker ratio to get the correct tappet lift. Since the parts kit includes the checking springs, the rest of the instructions will refer to degreeing the cam from the valve.
2.) Install the new cam and adjustable timing set per manufacturers instructions. Make sure both lobes for the #1 cylinder are free of any thick assembly lube that may throw off your readings. After the degreeing procedure re-lubricate the lobes.
3.) Install the degree wheel on the front of the crankshaft using your balancer bolt and the aluminum bushings. Attach the pointer at a convenient location, usually a bolt near the water pump. Align the pointer so that it is aimed directly at the center of the wheel and the tip is close to the edge of the wheel.
4.) Bring the #1 piston close to Top Dead Center (TDC) on the compression stroke (both valves closed). Without moving the crank, adjust the degree wheel so the pointer is at the TDC mark on the wheel. This is just to get you close to position.
5.)Turn the crankshaft 1/4-turn counterclockwise to lower the piston, then install the piston in the #1 spark plug hole. Screw the center post on the stop all the way in. Gently turn the crank clockwise until the piston hits the stop and record the reading. Turn the crankshaft in the opposite direction until the piston comes back up and hits the stop, then record that reading.
1.) Install the checking springs on the #1 cylinder. If you don't wish to remove the existing valve springs, you can degree the cam directly off a solid lifter. Make sure the specs on the cam card are taken from the lifter also. If they are taken at the valve, divide the valve lift by the specified rocker ratio to get the correct tappet lift. Since the parts kit includes the checking springs, the rest of the instructions will refer to degreeing the cam from the valve.
2.) Install the new cam and adjustable timing set per manufacturers instructions. Make sure both lobes for the #1 cylinder are free of any thick assembly lube that may throw off your readings. After the degreeing procedure re-lubricate the lobes.
3.) Install the degree wheel on the front of the crankshaft using your balancer bolt and the aluminum bushings. Attach the pointer at a convenient location, usually a bolt near the water pump. Align the pointer so that it is aimed directly at the center of the wheel and the tip is close to the edge of the wheel.
4.) Bring the #1 piston close to Top Dead Center (TDC) on the compression stroke (both valves closed). Without moving the crank, adjust the degree wheel so the pointer is at the TDC mark on the wheel. This is just to get you close to position.
5.)Turn the crankshaft 1/4-turn counterclockwise to lower the piston, then install the piston in the #1 spark plug hole. Screw the center post on the stop all the way in. Gently turn the crank clockwise until the piston hits the stop and record the reading. Turn the crankshaft in the opposite direction until the piston comes back up and hits the stop, then record that reading.
10-28-2006, 02:03 PM
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6.) If your original TDC estimation was correct, you'll have an equal amount of travel on either side of TDC (34 degrees BTDC and 34 degrees ATDC, for example). In most cases you'll have unequal readings, such as 38 degrees BTDC and 30 degrees ATDC. In this case, just split the difference and adjust the degree wheel without moving the crank. Here is an example:
38 degrees - 30 degrees = 8 degrees
8 degrees / 2 = 4 degrees
7.) Be sure to check the accuracy of your adjustment by turning the degree wheel from stop to stop again. You should have an equal amount of travel on each side of TDC.
8.) Place a solid lifter of the type that matches your cam on the #1 intake lobe. Install the appropriate pushrod and rocker on the same valve. If an adjustable pushrod is available, use it; you can make it longer to compensate for the shorter mechanical lifter and keep the geometry the same.
9.) Place the dial indicator and magnetic base on the cylinder head. If you have aluminum heads, you'll need to mount a flat piece of steel to the valve cover mounting holes for the magnetic base to attach to. Pre-load the dial indicator a little more than your maximum valve lift, and be sure the probe on the dial indicator is resting on the valve spring retainer and in alignment with the travel of the valve. This will reduce any geometric error in the valve lift measurements.
10.) Rotate the engine clockwise until you reach the point of maximum lift. Start slowing down as the needle slow down. When the needle stops moving you have reached the point of maximum lift. Double check the indicator probe to see if it is still touching the valve spring retainer. If you didn't pre-load the indicator enough, the probe will be resting gin the air. That will stop the movement of the needle, but the cam won't be at max lift.
38 degrees - 30 degrees = 8 degrees
8 degrees / 2 = 4 degrees
7.) Be sure to check the accuracy of your adjustment by turning the degree wheel from stop to stop again. You should have an equal amount of travel on each side of TDC.
8.) Place a solid lifter of the type that matches your cam on the #1 intake lobe. Install the appropriate pushrod and rocker on the same valve. If an adjustable pushrod is available, use it; you can make it longer to compensate for the shorter mechanical lifter and keep the geometry the same.
9.) Place the dial indicator and magnetic base on the cylinder head. If you have aluminum heads, you'll need to mount a flat piece of steel to the valve cover mounting holes for the magnetic base to attach to. Pre-load the dial indicator a little more than your maximum valve lift, and be sure the probe on the dial indicator is resting on the valve spring retainer and in alignment with the travel of the valve. This will reduce any geometric error in the valve lift measurements.
10.) Rotate the engine clockwise until you reach the point of maximum lift. Start slowing down as the needle slow down. When the needle stops moving you have reached the point of maximum lift. Double check the indicator probe to see if it is still touching the valve spring retainer. If you didn't pre-load the indicator enough, the probe will be resting gin the air. That will stop the movement of the needle, but the cam won't be at max lift.
10-28-2006, 02:15 PM
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11.) If everything is OK, turn the face of the dial indicator to zero. Turn the crank until you reach .050" before max lift and mark the position on the wheel. Continue turning the crank until the needle indicates .050" after max lift and record the reading. Add the two readings together and divide by two. For example:
150 degrees on one side
66 degrees on the other side
150 + 66 = 216 degrees
216 / 2 = 108 degrees
12.) This result (108 degrees in our example) will be the point of maximum lift, which is the theoretical intake centerline. If you're within one degree of the specification on the cam card, you're all set. If you are further off than that, you must adjust the cam's position and repeat the degreeing procedure. If you got a smaller number, the cam is advanced and would need to be retarded. Say in our example the cam came out at 106 degrees instead of 108. That means it is advanced and you would need to retard it two degrees. Getting a larger number than what is on the cam card means that the cam is retarded. In our example, getting 110 degrees reading for a cam speced at 108 indicates the cam is two degree retarded, so you would have to advance it two degrees.
13.) Once the intake centerline is correct, check the opening and closing points of the #1 intake valve at .050" lift. Pre-load the indicator as before and turn the crank in the same direction until the valve closes. The needle will stop moving since it will be on the heel of the lobe. Set the indicator face to zero, then slowly turn the crank until the needle just starts to rise as the valve opens. Turn very slowly until the needle reads .050" of valve lift. Record the reading on the degree wheel, then turn the crank and count the revolutions of the needle from .050" open until the valve reaches maximum lift. At that point, the needle will momentarily stop, then change direction.
150 degrees on one side
66 degrees on the other side
150 + 66 = 216 degrees
216 / 2 = 108 degrees
12.) This result (108 degrees in our example) will be the point of maximum lift, which is the theoretical intake centerline. If you're within one degree of the specification on the cam card, you're all set. If you are further off than that, you must adjust the cam's position and repeat the degreeing procedure. If you got a smaller number, the cam is advanced and would need to be retarded. Say in our example the cam came out at 106 degrees instead of 108. That means it is advanced and you would need to retard it two degrees. Getting a larger number than what is on the cam card means that the cam is retarded. In our example, getting 110 degrees reading for a cam speced at 108 indicates the cam is two degree retarded, so you would have to advance it two degrees.
13.) Once the intake centerline is correct, check the opening and closing points of the #1 intake valve at .050" lift. Pre-load the indicator as before and turn the crank in the same direction until the valve closes. The needle will stop moving since it will be on the heel of the lobe. Set the indicator face to zero, then slowly turn the crank until the needle just starts to rise as the valve opens. Turn very slowly until the needle reads .050" of valve lift. Record the reading on the degree wheel, then turn the crank and count the revolutions of the needle from .050" open until the valve reaches maximum lift. At that point, the needle will momentarily stop, then change direction.
10-28-2006, 02:24 PM
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14.) Continue turning the crank as the valve closes and the needle makes the same number of turns until the valve is a .050" before being fully close. Record the reading on the degree wheel, then compare both readings to the specifications on the cam card. Again, if they are within one degree they are fine. If not, the cam position will need to be adjusted. Follow your timing set instructions on making any adjustment. Recheck after you're done.
Note: When checking opening and closing points, look at the cam card to see if the .050" lift is measured at the lifter or the valve. If it is measure at the lifter, you need to multiply the lift figure by your rocker ratio since you are measuring at the valve.
15.) Set up the indicator, lifter, and proper pushrod on the exhaust lobe of the #1 cylinder for a quick check of the maximum lift, lobe center, and opening and closing points.
16.) Now that the cam is correctly positioned, remove your checking equipment and recoat the #1 lobes and lifters with your cam maker's recommended break-in lube. Replace the checking springs with the originals and assemble the remainder of the engine. Pay close attention to getting the engine ready to start immediately after the key is turned. Put a timing light on the #1 plug wire and have the fuel system primed and ready to flow. Quick startup and proper cam break-in is essential. Make sure to follow all of your cam maker's break-in instructions to get the maximum performance life possible out of your camshaft.
And that's it!
Note: When checking opening and closing points, look at the cam card to see if the .050" lift is measured at the lifter or the valve. If it is measure at the lifter, you need to multiply the lift figure by your rocker ratio since you are measuring at the valve.
15.) Set up the indicator, lifter, and proper pushrod on the exhaust lobe of the #1 cylinder for a quick check of the maximum lift, lobe center, and opening and closing points.
16.) Now that the cam is correctly positioned, remove your checking equipment and recoat the #1 lobes and lifters with your cam maker's recommended break-in lube. Replace the checking springs with the originals and assemble the remainder of the engine. Pay close attention to getting the engine ready to start immediately after the key is turned. Put a timing light on the #1 plug wire and have the fuel system primed and ready to flow. Quick startup and proper cam break-in is essential. Make sure to follow all of your cam maker's break-in instructions to get the maximum performance life possible out of your camshaft.
And that's it!
10-28-2006, 06:19 PM
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Car: 89rs
Engine: 400Sb
Transmission: Tremec 3550
Good effort. Just a little more practical info:
In general, unless it is a custom ground cam, all most all are ground with a 4 degree advance. If the lobe separation angle is 110, the intake centerline will be probably 106. That will make the exhaust 114 centerline. If it comes up something other than that, it is probably pretty nonstandard. Also in general (especially if you are installing it in the motor for the first time - you really dont know if it might need to be advanced or retarded to improve the performance for your combination) you really cant improve on the original intake centerline.
The short answer is, make sure it has the proper manufacture intake centerline and try it there. If you need to move the power band around (which is kind of tough for a non-custom ground cam), do that AFTER you have spent some time trying it on the factory intake centerline.
In general, unless it is a custom ground cam, all most all are ground with a 4 degree advance. If the lobe separation angle is 110, the intake centerline will be probably 106. That will make the exhaust 114 centerline. If it comes up something other than that, it is probably pretty nonstandard. Also in general (especially if you are installing it in the motor for the first time - you really dont know if it might need to be advanced or retarded to improve the performance for your combination) you really cant improve on the original intake centerline.
The short answer is, make sure it has the proper manufacture intake centerline and try it there. If you need to move the power band around (which is kind of tough for a non-custom ground cam), do that AFTER you have spent some time trying it on the factory intake centerline.
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