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Glossary

The purpose of publishing this information is to acquaint the cam customer with cam terms as generally used by cam manufactures, in order that they may be able to purchase, install, use and discuss special camshafts in a common language.

ABDC : After Bottom Dead Center..

AREA UNDER CURVE : The amount of area under the charted curve, a tool of the cam grinder, to compare lift, duration and general size of the cam profile..

ATDC : After Top Dead Center..

BARREL FLEX : Deflection or bending of the cam barrel or core, common in smaller diameter cams..

BARREL OR CORE : The main shaft portion of the camshaft..

BASE CIRCLE : The base of the cam lobe that is round and concentric with the journals (also known as the ‘heel’).

BBDC : Before Bottom Dead Center.

BLOW-DOWN DURATION : The period of time necessary for the cylinder pressure to drop to atmospheric pressure after the exhaust valve opens..

BOOST : The amount of pressure over atmospheric pressure in the manifold, usually described by p.s.i. or inches of mercury..

BTDC : Before Top Dead Center.

CAM FOLLOWER : Also called "Lifter". The component that follows the camshaft lobe and transfers the action of the cam to the rest of the valve train by riding on the camshaft lobe surface,.

CAM JOURNALS : The diameters on a camshaft which provide bearing areas.

CAM LIFT : The distance that the cam raises the lifter. .

CAM LUBE : A lubricant that is applied to the cam lobes before installing a camshaft to prevent wear during the break in period (the first 20 minutes of operation)..

CAM MASTER : A precision template that is used in the camshaft grinder to transfer the preferred lobe shape type the camshaft during production..

CAM PROFILE : The shape of a cam lobe..

CAMSHAFT : A shaft with multiple cams attached or integrally manufactured to actuate a cam follower. A cam is a rotating or sliding piece in a mechanical linkage used especially in transforming rotary motion into linear motion or vice-versa. The camshaft determines when the valves open and close, how long and how far they open..

CASTING : A metal object which was by molten metal or other material being poured into a mold. Casting is a manufacturing process by which a liquid material is usually poured into a mold, which contains a hollow cavity of the desired shape, and then allowed to solidify. .

CLEARANCE RAMPSThe ‘take-up’ portion of the lobe extending from the base circle to the point where valve actuation occurs..

COIL BIND : The point at which a valve spring that has been compressed to the point where the coils are stacked and there is no space left between the coils. .

CONCENTRIC : Running true or having the same center..

CORE DIAMETER : The diameter of the camshaft measured in-between the cam lobes..

DOHC : Dual over head cam.

DURATION AT THE CAM : Number of degrees measured at the cam from opening to closing at a given checking height. Crower cam cards list the cam duration figures at .050” lift..

DURATION AT THE VALVE : The same as duration at the cam except as measured at the valve, which is changed the ratio of the rocker arm..

DURATION : The number of degrees in which the valve is off the seat. The duration of a camshaft is usually related to the RPM range that is desired. For example: a tow truck that will see a 5000 RPM maximum would pull best with a cam around 255° duration. A passenger car with RPM range up to 5500 would like around 265° duration. A street-strip car, in order to perform well at the drags would require around 300°, and a sacrifice in low end street performance would be present. A non street gasser (unblown) would require 310-330° duration, and the blown gasser or fueler would require around 330-360° duration..

EXHAUST RETURN : The portion of the exhaust which may return to the cylinder after blow-down, due to a below atmospheric pressure condition caused by exhaust exit inertia. An undesirable occurrence, attributed to exhaust pipes which are too small in diameter, or too long, or both..

FLANK : The portion of the lobe, from the point of valve actuation to the nose of the lobe..

FLAT FACE LIFTER : A hydraulic or mechanical lifter which slides on the camshaft lobe surface. The flat face lifter rotates slowly on the taper ground into the cam lobe as it slides along the lobe surface..

FLOAT : The occurrence of the follower leaving the lobe at higher RPM’s, commonly due to poor lobe design..

FORGING : A process which a metal billet is struck with great pressure, while in a red hot state to create the desired shape. Forging can produce a object that is stronger than an equivalent cast or machined part. As the metal is shaped during the forging process, its internal grain deforms to follow the general shape of the part. As a result, the grain is continuous throughout the part, giving rise to a piece with improved strength characteristics.

HARDFACE : Usually a weld to apply a tungsten carbide, chrome-nickel alloy to the outer surface of the cam lobe. This process creates an extra-durable surface for the high spring pressures and high rpm of some extreme applications..

IMPERIALIZE : To manufacture or install roller bearings in the cam journals to eliminate the friction of plain bearings..

INDUCTION HARDENED : A process of heat treating where an object is placed inside a electric coil of heavy wire through which high frequency current is passed. Through the electrical properties of this induction coil, the object inside becomes heated in a defined area or areas instantly and is then quenched in oil..

INTAKE REVERSAL : A pushing back of the intake fuel/air mixture caused by short intake column length, excessive intake duration, or improperly tuned exhaust system. More evident at full throttle, low RPM..

INTAKE VELOCITY : The speed at which the air/fuel mixture travels while moving in the intake port..

INTERFERENCE FIT : In a dual, where the outer spring and inner spring fit together with a slight press. This produces a dampening effect on valve spring vibration and surge..

LASH : The same as VALVE LASH. This is the clearance between the valve tip and the rocker. Crower lists the recommended Valve Lash on the timing tag that is supplied with each camshaft, These numbers are specific to each camshaft. The lash is measured at the cam on over head cam engines..

LIFT GRADE : A charted curve of the valve lift per camshaft rotation..

LIFT : The total travel of the valve from the seated position to full open. This requirement varies from engine to engine, but generally speaking, if performance is the prime concern, the highest lift that can be run in the limitations of valve springs, RPM, duration, and life of valve guides, is the best. For example, a .600 lift would not be practical for a street engine because valve guides would be prone to early wear; however, for a large displacement wedge engine requiring 340° to 350° duration, and an operating range up to 9000 RPM, this lift would be very practical. Also, to attempt to use a .600’’ lift and 250° duration would be poor judgment as it would make the valve lift rate so severe that it would break valve train components. The highest useful lift is an average of all the factors involved in a particular engine and its use..

LOBE CENTER : The angular displacement between the center line of the intake lobe, and exhaust lobe of the same cylinder. This factor may be altered in order to ‘fine-tune’ the combustion chamber. For example an engine using the general lobe center of 110° would have a split overlap timing of 40-80 80-40. If for some reason, more low end power plus a cooler combustion chamber were desired, the lobe center could be changed to 105°, which would give the timing of 45-75 75-45 using the same cam master. Some high nitro, blown engines, may use a 100° lobe center cam which would give more combustion chamber cooling, in order to accommodate the high heat of the nitro mixture. A 340° cam with a 100° lobe center would have a timing of 70-90 90-70..

LOBE : The lobe is eccentric to the cam bearings of the camshaft and transmits a lifting motion through the valve train to operate the valves. .

NITRIDING : Nitriding is a surface heat treatment which leaves a hard case on the bearing surfaces of a crankshaft. .

NORMALLY ASPIRATED : An engine that utilizes either carburetors or fuel injection not mechanical device that forces a fuel and air mixture into the combustion chambers..

NOSE OF THE LOBE : The highest portion of the cam lobe. The full lift position..

OHC : Overhead cam engine. In this type of engine the camshaft is positioned above the valves. .

OVERLAP : The number of degrees in which both intake and exhaust valves are open to accomplish combustion chamber scavenging..

PARKO OR PARKERIZING : A thermo-chemical, oil-absorptive coating which applied to the outside surface of the camshaft. This helps initial break-in of the cam lobes..

PRE-LOAD : To lightly load with pressure before applying a greater load..

PROFERAL OR PRO 55 : A superior quality cast iron alloy. Used higher load, extreme profile camshafts because of its excellent durability..

RAM : The term applied to the effect caused by the intake air column packing the cylinder to an above atmospheric pressure..

ROLLER LIFTER : A lifter that uses a roller bearing to roll over the cam lobe surface instead of sliding like a flat face lifter. Camshafts made for Roller lifter application do not have taper ground into the lobe surface..

SEAT BOUNCE : An undesirable condition occurring at high RPM’s when the valve touches the seat, reopens due to excessive seating velocity. Usually due to poor cam lobe design..

SEAT DURATION : The total time (measured in degrees of crankshaft rotation) that the valve is off of its valve seat from opening until when it closes..

SOHC : Single over head cam..

SPLITTING THE OVERLAP : The starting point on Cam Positioning. A common error in camshaft installation with regard to being improperly timed the crankshaft. There are several reasons why a camshaft can be out of time. They are (1) Improperly marked timing gears, (2) Chain stretch, (3) Indexing error on welded strokers. These inconsistencies can be overcome by splitting the overlap – that is, advancing or retarding the cam (when the crank is on T.D.C. EXHAUST) so that the intake and exhaust lifter have equal lift at this point. Simply use a straight edge (ruler, tool bit, etc.) to check the top of the lifter. This is the place to begin with any Crower Cam. From here, the Cam may be advanced to give more low end power, or retarded to give more top end power. Be sure to check ignition timing after making a change in cam positioning..

SPRING DAMPENER : A flat coiled metal strip, usually inside the outer spring which due to friction, tends to reduce undesirable spring harmonics..

SPRING HARMONICS : Stages in the RPM range when springs fail to provide the designed load to the spring retainer, due to self-contained inertia problems in the spring wire..

STOCK LIFT CAM : This cam has stock lift , but the duration and flanks are modified so that they are faster acting..

SWEEP : The amount of travel the cam lobe has across the lifter face. Lifter diameter determines flank velocity..

TAPER : This is the amount by which the diameter of the front of the base circle differs from the diameter of the rear of the base circle. Lobe taper effects the speed of rotation of the lifter. If the lifter does not rotate at the proper speed, premature lifter and cam wear will occur..

TIMING EVENTS : The opening and closing points of the valve with relation to the crankshaft. Crower timing tags include the timing events for each specific cam..

VALVE ACTION : The speed at which the valve opens and closes is also a factor, which is related to the RPM range of the engine. The low RPM engine may use a faster action than the high RPM engine, Should the low RPM engine have a short duration ‘slow action’ cam, the area under the lift curve would not provide the air flow necessary for good performance. If the high RPM engine has a fast action cam, most likely the valve float would occur prematurely..

VALVE BOUNCE : When there is a lack of adequate valve spring pressure or where a poorly designed cam is used, The valve lands with such force on the valve seat that it has a tendency to bounce back up again, causing a loss of power and resulting in engine damage..

VALVE FLOAT : A detrimental condition caused by mis-matched components ,poor cam design, over revving the engine, or by inadequate valve spring open pressure, resulting in a condition where the lifter and other valve train components fail to follow the cam profile..

VALVE LASH : This is the clearance between the valve tip and the rocker or cam bucket or measured at the cam on over head cam engines. Crower lists the recommended Valve Lash on the timing tag that is supplied with each camshaft, These numbers are specific to each camshaft..

VALVE LIFT : The lift of the valve. This lift can be determined by multiplying cam lift by rocker ratio and subtracting the valve lash..

VALVE TRAIN : All components used to open and close the valves. .