How To Determine Cam Specifications of an Unknown Cam
03-22-2005, 11:10 AM
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How To Determine Cam Specifications of an Unknown Cam It isn't really that hard to figure out what the specs of your cam are. It would be easier to check the specs in the vehicle than it would be to pull the cam out, send it to have it checked, and re-install it. I have checked several cams this way. You might not be EXACT but you will be within a couple of degrees if you follow my directions:
(1) Remove the valve cover, spark plug, and rocker arms on #1 cylinder.
(2) You have to find TDC (Top Dead Center) of cylinder #1. Older cars had marks on the balancer, but several ways to do this exist for unmarked balancers. I prefer to accomplish this by pushing ~2 feet of clothesline or 1/4" nylon rope into the spark plug hole. (Be sure to leave some rope hanging out of the hole for later removal). Then rotate the crank clockwise by hand until it stops. Make an alignment mark on the balancer and timing cover. Then rotate the crank counterclockwise until it stops and make another mark on the timing cover. Remove the rope. Make a third mark on the timing cover exactly 1/2 way between the marks. When the balancer aligns with this third mark, it will be at TDC. Erase the other two marks to avoid confusion.
(3) Wrap masking tape - I suggest the better "blue" or "green" painters type so it is reusable, around the balancer, starting at the TDC mark. Remove the tape without ripping it, and measure it's length to get the balancer's circumference. Timing tapes are available for many engines but I don't know if there are any for the LS1 balancer circumference (length). To make your own, Divide the cicumference measurement by 360 to determine how many millimeters of balancer rotation equal 1 degree. (Or divide by 90 like I do to equal 4 degrees). You can now mark the tape accordingly and re-install on the balancer mark.
(4) Obtain a dial indicator. Mount it so it will indicate the movement of the intake pushrod as the crank turns.
(5) Slowly turn the balancer clockwise until the indicator shows .050" movement. Write on a notepad the number of degrees this occurs at. Continue rotating clockwise and make a note of the maximum lift observed. Continue rotating clockwise until the indicator is .050" from the "0" (or closed) position. Record that number of degrees. It is important to only make the degree measurements when rotating in a clockwise direction to prevent a false reading due to slack in the timing chain. If you have to reverse the balancer rotation, such as when you miss the .050" mark, just go counterclockwise at least 30-40 degrees before turning it clockwise again. That will remove the slack from the timing chain again.
(6) Install the dial indicator on the exhaust pushrod and repeat step #5 for the exhaust side.
(7) you now can convert your rotation degree readings to degrees BTDC (before top dead center) , ABDC (after bottom dead center), BBDC, and ATDC. Note that 180* is BDC. So 135* balancer rotation would be 45* BBDC. 227* rotation would be 47*ABDC.
Your cam's LSA (lobe seperation angle) can also be determined by the information obtained above. PM me if you need help converting the measurements.
PS - It helps to make a timing "pointer" out of a piece of coat hanger to replace the alignment mark on the timing cover. Attach one end to a timing cover bolt, then align the other end of the wire with the mark on the cover and have it point at the tape.
(1) Remove the valve cover, spark plug, and rocker arms on #1 cylinder.
(2) You have to find TDC (Top Dead Center) of cylinder #1. Older cars had marks on the balancer, but several ways to do this exist for unmarked balancers. I prefer to accomplish this by pushing ~2 feet of clothesline or 1/4" nylon rope into the spark plug hole. (Be sure to leave some rope hanging out of the hole for later removal). Then rotate the crank clockwise by hand until it stops. Make an alignment mark on the balancer and timing cover. Then rotate the crank counterclockwise until it stops and make another mark on the timing cover. Remove the rope. Make a third mark on the timing cover exactly 1/2 way between the marks. When the balancer aligns with this third mark, it will be at TDC. Erase the other two marks to avoid confusion.
(3) Wrap masking tape - I suggest the better "blue" or "green" painters type so it is reusable, around the balancer, starting at the TDC mark. Remove the tape without ripping it, and measure it's length to get the balancer's circumference. Timing tapes are available for many engines but I don't know if there are any for the LS1 balancer circumference (length). To make your own, Divide the cicumference measurement by 360 to determine how many millimeters of balancer rotation equal 1 degree. (Or divide by 90 like I do to equal 4 degrees). You can now mark the tape accordingly and re-install on the balancer mark.
(4) Obtain a dial indicator. Mount it so it will indicate the movement of the intake pushrod as the crank turns.
(5) Slowly turn the balancer clockwise until the indicator shows .050" movement. Write on a notepad the number of degrees this occurs at. Continue rotating clockwise and make a note of the maximum lift observed. Continue rotating clockwise until the indicator is .050" from the "0" (or closed) position. Record that number of degrees. It is important to only make the degree measurements when rotating in a clockwise direction to prevent a false reading due to slack in the timing chain. If you have to reverse the balancer rotation, such as when you miss the .050" mark, just go counterclockwise at least 30-40 degrees before turning it clockwise again. That will remove the slack from the timing chain again.
(6) Install the dial indicator on the exhaust pushrod and repeat step #5 for the exhaust side.
(7) you now can convert your rotation degree readings to degrees BTDC (before top dead center) , ABDC (after bottom dead center), BBDC, and ATDC. Note that 180* is BDC. So 135* balancer rotation would be 45* BBDC. 227* rotation would be 47*ABDC.
Your cam's LSA (lobe seperation angle) can also be determined by the information obtained above. PM me if you need help converting the measurements.
PS - It helps to make a timing "pointer" out of a piece of coat hanger to replace the alignment mark on the timing cover. Attach one end to a timing cover bolt, then align the other end of the wire with the mark on the cover and have it point at the tape.
05-06-2005, 10:59 PM
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I thought somebody else might want to know how to figure out the camshaft specs for a "performance package" or H/C kit that they paid big bucks for.
I thought somebody else might want to know how to figure out the camshaft specs for a "performance package" or H/C kit that they paid big bucks for.
