measuring valve lift ?
03-10-2009, 10:20 PM
#1
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measuring valve lift ?
what's the easiest way to measure the lift of my cam while it's still in the engine . & is it cam lift or valve lift ? thanks .
03-11-2009, 12:23 AM
#2
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Well "Valve Lift" is the distance that the valve is opened. I can tell you that much but i am not as knowledgable as the rest of the guys here. So i am not exactly sure what you are looking to measure. I found this, it might help I hope.
Valve Lift - To figure valve lift take the distance that the cam lobe lifts the tappet and multiply it by the rocker arm ratio, this will give you the distance that the valve is opened or "valve lift".
Duration - This is the time that the valve is off the seat during tappet lift, measured in CRANKSHAFT degrees. As there has to be some point in which you begin to measure the lift of a cam there are usually two figures given on a spec card. The Advertised Duration and the Duration at some arbitrarily chosen point (Usually .050" lift) Some manufacturers measure duration at a different amount of lift and this can cause confusion. Most Cam manufacturers use the .050" figure, but it is wise to be sure when comparing different grinds. When checking a cam you should always check it at the tappet rather than the valve because of minor variations due to lash, and rocker arm ratio.
Centerline - The Centerline of a Cam is the actual position or phasing of the cam in relation to the Crankshaft. Meaning the position of the center line of the #1 INTAKE lobe of the cam in relation to the position of the #1 piston measured in crankshaft degrees of rotation AFTER TDC.
Lobe Separation - This is the PHYSICAL configuration of the cam in relation to the actual spacing of the intake and exhaust lobes from each other. Lobe separation is ground into the camshaft. You CANNOT change it (Unless you regrind the cam). You CAN change the Centerline by degreeing. These two terms are often confused with each other.
Symmetrical- A cam that is Symmetrical has both sides of the cam lobe exactly the same. In other words, the intake ramp of the cam lobe that accelerates the lifter to actuate the valve has the same shape as the portion of the ramp on the downside of the lobe that lowers the lifter. These designs are very easy on the valve train as it is a smooth transition from open to closed.
Asymmetrical - An Asymmetrical cam has opening and closing ramps that are different. These profiles are usually found on high performance cams and offer a high velocity opening and a lower velocity closing ramp in order to snap the valve open quickly and then set it back down more gently.
Dual Pattern - Again, a grind that is usually found in a high performance cam. The Intake lobe configuration is different from the exhaust lobe. Usually the exhaust lobe is ground with slightly more duration that the intake lobe. Cam Walk - A phenomenon that occurs with Roller cams due to slight inaccuracies in the lifter bore spacing. Most Roller cams use a cam button to control the tendency of the cam to unscrew itself from the block. Bushing the lifter bores can control this problem but is very expensive. A cam button will work quite well in 99% of cases.
Valve Lift - To figure valve lift take the distance that the cam lobe lifts the tappet and multiply it by the rocker arm ratio, this will give you the distance that the valve is opened or "valve lift".
Duration - This is the time that the valve is off the seat during tappet lift, measured in CRANKSHAFT degrees. As there has to be some point in which you begin to measure the lift of a cam there are usually two figures given on a spec card. The Advertised Duration and the Duration at some arbitrarily chosen point (Usually .050" lift) Some manufacturers measure duration at a different amount of lift and this can cause confusion. Most Cam manufacturers use the .050" figure, but it is wise to be sure when comparing different grinds. When checking a cam you should always check it at the tappet rather than the valve because of minor variations due to lash, and rocker arm ratio.
Centerline - The Centerline of a Cam is the actual position or phasing of the cam in relation to the Crankshaft. Meaning the position of the center line of the #1 INTAKE lobe of the cam in relation to the position of the #1 piston measured in crankshaft degrees of rotation AFTER TDC.
Lobe Separation - This is the PHYSICAL configuration of the cam in relation to the actual spacing of the intake and exhaust lobes from each other. Lobe separation is ground into the camshaft. You CANNOT change it (Unless you regrind the cam). You CAN change the Centerline by degreeing. These two terms are often confused with each other.
Symmetrical- A cam that is Symmetrical has both sides of the cam lobe exactly the same. In other words, the intake ramp of the cam lobe that accelerates the lifter to actuate the valve has the same shape as the portion of the ramp on the downside of the lobe that lowers the lifter. These designs are very easy on the valve train as it is a smooth transition from open to closed.
Asymmetrical - An Asymmetrical cam has opening and closing ramps that are different. These profiles are usually found on high performance cams and offer a high velocity opening and a lower velocity closing ramp in order to snap the valve open quickly and then set it back down more gently.
Dual Pattern - Again, a grind that is usually found in a high performance cam. The Intake lobe configuration is different from the exhaust lobe. Usually the exhaust lobe is ground with slightly more duration that the intake lobe. Cam Walk - A phenomenon that occurs with Roller cams due to slight inaccuracies in the lifter bore spacing. Most Roller cams use a cam button to control the tendency of the cam to unscrew itself from the block. Bushing the lifter bores can control this problem but is very expensive. A cam button will work quite well in 99% of cases.
03-11-2009, 01:22 AM
#3
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Darn computer tossed my answer away just as I was finishing reply. Man it was a good reply. I'll try to remember it all & send later today. Sleepy now.
03-11-2009, 02:28 AM
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03-11-2009, 02:58 AM
#5
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03-11-2009, 06:15 AM
#6
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Thats about the best way to do it DK. I would make sure that the indicator is on a solid part of the lifter to get a more accurate measurement and do it a few times.
03-11-2009, 10:45 PM
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