* A positive stop device to locate TDC. You can make one of these by using a piece of angle iron that is bolted to the block at the head bolts with a bolt protruding into the cylinder. An old spark plug with the porcelain drilled out and tapped for a bolt that will act as the positive stop can also be used when the heads are in place.

Camshaft Terms
Asymmetrical Lobe: A camshaft's lobe that has a different profile on both the opening side and the closing side.

Base Circle: Is the backside (heel) of the camshaft lobe.

Centerline: The point of a lobe that has the maximum amount of lift. This is commonly used as a reference point when degreeing a camshaft.

Degree Wheel: A flat metal disk with measurement in degrees. The measurements start at 0 degrees going a full 360 degrees in increments of 1 degree or less than 1 degree. A degree wheel is bolted onto the crankshaft while in use.

Dial Indicator: A measuring instrument used to measure rotating parts, such as cam lobes.

Duration: How long a valve is open during crankshaft rotation. This is usually measured at 0.050-inch of valve lift on the opening side of the lobe to 0.050 on the closing side of the lobe because there is little airflow at low lift values. It is stated in degrees of crankshaft rotation.

Lift: The distance a valve rises off the valve seat. This can vary depending on the rocker arm ratio, valve lash and pushrod deflection.

Lobe Separation (angle): This is the degrees measured between the maximum lift on the intake lobe and the maximum lift on the exhaust lobe. This cannot be changed without regrinding the camshaft.

Positive Stop Device: A tool that is used to prevent motion beyond a given point.

Adjustment, Advancing, Or RetardingIf the camshaft isn't corresponding to the cam card, there are several methods of adjustment that will move the camshaft into the correct position. The smaller sprocket on many timing-chain sets has three or more keyways. By using any of the different keyways you can advance or retard the camshaft. When using this method, there are matching numbers on the larger sprocket that need to be matched to what you set the smaller sprocket on. Also, you can use eccentric bushings in the upper sprocket. These bushings are put in the aligning dowel pinholes and can be turned to advance or retard the camshaft timing. When using this method, the mounting holes will need to be drilled out so there is room for the gear to be rotated. Another option is the use of an offset key on the crankshaft. This method, just like the multiple keyways in the smaller sprocket, works by turning the gear to either advance or retard the camshaft timing.

Do not confuse advancing or retarding the camshaft with degreeing it. Degreeing the cam consists of checking the installed centerline location of the camshaft and the opening and closing point of the lifters at 0.050 inches on the lobe. Advancing or retarding the cam by use of cam gear bushings or the crank gear changes only the installed position of the cam relative to the crankshaft. When you change the cam's phasing, it causes all lobes to open or close sooner or later relative to the position of the crankshaft.

You might want to advance or retard your camshaft to increase performance. By advancing or retarding the cam, you can change the torque curve to better match track conditions. For example, and depending on the cam's grind, a 2-degree advance of the camshaft can move the powerband approximately 100 rpm sooner, while the same degrees of retard can cause the powerband to come on 100 rpm later.

SOURCE
Crane Cams
530 Fentress Blvd.
Daytona Beach
FL  32114
3-86/-252-1151
N/A
www.cranecams.com
Dave Pletcher Racing
4470 63rd Cir. N.
Pinellas Park
FL  33781