ABDC: After Bottom Dead Centre.

ATDC: After Top Dead Centre.


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 Centre.

BTDC: Before Top Dead Centre.


CAM FOLLOWER: Usually a flat faced or roller companion to the camshaft, which transfers the action of the camshaft to the rest of the valve-train by sliding or rolling on the cam lobe surface.

CAM LIFT: The distance that the cam raises the lifter - Not to be confused with valve lift.

CAM LUBE: A non-detergent lubricant containing Molybdenum-Disulphide which is spread on the cam lobes when installing a camshaft, to prevent galling and insure protection during the critical break-in period (the first 20 minutes of operation).

CAM MASTER: After the design of the cam is computed, it is transferred to a precision template, or master. The master is then installed in the cam grinding machine to generate the shape of the lobes of the production cam.

CAM PROFILE: The actual shape of the cam lobe.

CAMSHAFT: A shaft containing many cams that convert rotary motion to reciprocating (lifting) motion. For every two revolutions of the crankshaft, the camshaft rotates one revolution. The lobes on the camshaft actuate the valve train in relation to the piston movement in an internal combustion engine. The camshaft determines when the valves open and close, how long they stay open, and how far they open.

CHEATSTOCK CAM: The improved stock cam, this has stock lift and sometimes stock duration (depending on the class rules), but the flanks are modified so that they are faster acting. This process adds about a 5% increase in the area under the lift curve. This means there will be a power increase during the entire RPM range of the engine. This type of grind works very well in engines that have fuel injection systems that run off of manifold vacuum and are therefore very sensitive to camshaft duration changes.

CHILLED IRON LIFTER: A cam follower made from high quality iron alloy, which is surface hardened by pouring the molten iron into a honeycomb mould with a chilled steel plate at the bottom resulting in a denser and harder lifter surface (compatible with steel and hard face overlay cams only).

CLEARANCE RAMPS: The portion of the cam lobe just up off the base circle which lifts at a slower speed than the flank. Its purpose is to dampen or ease the initial lifter motion, rather than opening and closing suddenly. Ramps on hydraulic lifter engines are very small, maybe only as high as .003” and only serve as noise reduction devices because the dampening effect is mostly catered for by the hydraulic lifter. Ramps on solid lifter camshafts are much higher, anywhere from .006” to .020” (ramp height multiplied by your rocker ratio equals your maximum valve clearance). Ramp designs have a tremendous effect on power output and valve-train reliability.

COIL BIND: A valve spring that has been compressed to the point where the coils are stacked solid and there is no space left between the coils. The valve cannot open any further when this happens.

CONCENTRIC: Running true or having the same centre. In camshaft terminology, the cam bearings and lobes are concentric to each other when the cam is straight and there is .001" or less runout between all the cam lobes and bearings.

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


DURATION AT THE CAM: Number of degrees measured at the cam from opening to closing (at a given checking height) E.g. on a Kelford Cams cam card for a pushrod style engine we state cam duration figures at .050” checking height.

DURATION AT THE VALVE: Number of degrees measured at the valve from opening to closing (at a given checking height) E.g. on a Kelford Cams cam card for a Japanese overhead cam engine we state valve duration figures at 1.00mm checking height.


FLANKS: The sides of the cam lobe or the portion of the lobe that lies between the nose and the clearance ramp on either side.

FORGED: A metal object which was formed under pressure, while in a red hot, or semi-molten state.


HARDFACE OVERLAY: A process to apply a tungsten carbide, chrome-nickel alloy to the outer surface of the cam lobe. These combined alloys provide an extra-durable surface for the tremendous spring pressures and high RPM of today's all-out competition engines. Kelford Cams use 50HRC or 60 HRC hard weld rod, depending on the application.


INDUCTION HARDENING: A process of electrical heat treating whereby an object is placed inside a coil of heavy wire through which high frequency current is passed. Through the electrical properties of this induction coil, the object inside the coil becomes cherry red almost instantly and is then quenched in oil.

INERTIA SUPERCHARGING: A condition created by the piston as it reaches the bottom of its intake stroke, by which the inertia of the intake air column continues to pack the cylinder until the pressure exceeds that of the atmosphere.

INTERFERENCE FIT: In a dual spring combination where the outside diameter of the inner spring and the inside diameter of the outer spring nearly approximate each other so that there is a slight press fit between the 2 springs. This produces a dampening effect on valve spring vibration and surge.


LASH (VALVE LASH) / TAPPET CLEARANCE: This is the clearance between the valve tip and the rocker or cam bucket (sometimes measured at the cam on overhead cam engines). Kelford Cams spec cards state where this is to be measured and whether to set the clearance hot or cold. Alloy block sprint car engines may have .015” clearance difference from hot to cold, therefore these engines need high clearance rampsand need to be set hot. The lash is relevant to your particular camshaft, not to the engine type, and must be set correctly so as not to run off the end of the clearance ramp.

LIFT CURVE: By installing the camshaft in a block or head, you can plot the lift of the cam in relation to each degree of camshaft rotation by installing a dial indicator on the valve retainer and a degree wheel on the crankshaft. All that is necessary is to rotate the crankshaft every 2 degrees and take a reading on the dial indicator at each of these intervals and transfer the readings to an Excel spreadsheet to produce a graph of the lift curve, from there you can deduce velocity, acceleration and jerk, to analyse the valve motion.

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. The design of the lobe determines the usage of the camshaft.

LOBE CENTRES (CAM): The distance measured in degrees between the centreline of the intake lobe and the centreline of the exhaust lobe in the same cylinder.

LOBE TAPER: This is the amount by which the diameter of the front of the base circle is different from the diameter of the rear of the base circle. The amount of taper can be anywhere from zero to .003" depending on the engine. If the forward side of lobe is greater than the rear side we say that the cam has taper left. If the back side of the lobe is greater than the front side then we say that the cam has taper right. Lobe taper has a dramatic effect on the speed of rotation of the lifter. If the lifter does not rotate at the proper speed, premature lifter and cam wear will occur.


NET VALVE LIFT: The actual lift of the valve. This lift can be determined by multiplying cam lift by rocker ratio and subtracting valve clearance (lash), if any.

NITRIDING: Gas nitriding is a surface heat treatment which leaves a hard case on the surface of the cam. This hard case is typically twice the hardness of the core material up to .010" deep. This process is accomplished by placing the cam into a sealed chamber that is heated to approximately 950 degrees Fahrenheit and filled with ammonia gas. At this temperature, a chemical reaction occurs between the ammonia and the cam metal to form ferrous nitride on the surface of the cam. During this reaction, diffusion of the ferrous-nitride into the cam occurs which leads to the approximate .004" case depth. The ferrous-nitride is a ceramic compound which accounts for its hardness. It also has some lubricity when sliding against other parts. The nitriding process raises and lowers the chamber temperature slowly so that the cam is not thermally shocked. Because of its low heat treat temperature, no loss of core hardness is seen. Gas nitriding was originally conceived where sliding motion between two parts takes place repeatedly so is therefore directly applicable to solving camshaft wear problems.

NORMALLY ASPIRATED / NATURALLY ASPIRATED: An engine that utilises either carburettors or fuel injection, without a mechanical device (i.e. supercharger, turbocharger, nitrous).that forces the fuel/air mixture into the combustion chambers.

NOSE OF THE LOBE: The highest portion of the cam lobe from the base circle (full lift position).


OHC: Overhead cam engine. In this type of engine the camshaft is positioned above the valves. DOHC = double overhead cam. SOHC = single overhead cam.

OHV (PUSHROD ENGINES): Overhead valve engines. In this type of engine the camshaft is positioned beneath the valves. (i.e. 350ci Chevrolet V8, Nissan A12 etc.)

OVERLAP: A situation where both the intake and exhaust valves are open at the same time when the piston is at top dead centre on the exhaust stroke. The greater the seat duration is on the intake and exhaust lobes, and the tighter the lobe separation, the greater the overlap will be (measured in degrees of crankshaft rotation).


PARKERIZING: A thermo-chemical application whereby a non-metallic, oil-absorptive coating is applied to the outside surface of the camshaft. This helps initial break-in without scuffing the cam lobes.

PRE-LOAD: To load before applying a different load for example setting a hydraulic lifter beyond zero clearance into preload by a set amount

PROFERAL IRON: A very high quality cast iron alloy. Used primarily for camshafts because of its excellent wearing ability.


ROLLER TAPPET: The roller tappet performs the same function as the mechanical or hydraulic tappet. However, instead of sliding on the cam face, the lifter contains a roller bearing which rolls over the cam surface.


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

SPLIT OVERLAP: An occurrence when both the intake valve and the exhaust valve are off their seats at the same time by the same amount at TDC.

SPRING FATIGUE: Valve springs have a tendency to lose their tension after being run in an engine for certain periods of time, because of the tremendous stress they are under. At 6,000 rpm, for example, each spring must cycle fifty times per second. The tremendous heat generated by this stress eventually effects the heat-treating of the spring wire and causes the springs to take a slight set (drop in pressure).

SPRING SURGE: The factor which causes unpredictable valve spring behaviour at high reciprocating frequencies. It's caused by the inertia effect of the individual coils of the valve spring. At certain critical engine speeds, the vibrations caused by the cam movement excite the natural frequency characteristics of the valve spring and this surge effect substantially reduces the available static spring load. In other words, these inertia forces oppose the valve spring tension at critical speeds.

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


VALVE BOUNCE: When there is a lack of valve spring tension, or where a poorly designed cam having excessive deceleration and velocity characteristics 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 harmful damage

VALVE EVENTS: The opening and closing points of the valve with relation to the crankshaft.

VALVE FLOAT: A detrimental condition caused by poor cam design mismatched components, over revving the engine, or by inadequate valve spring open pressure, resulting in a lag of the valve gear components where they fail to follow the cam profile.

VALVE LASH: Same as valve clearance or tappet clearance, necessary to allow for thermal expansion of the valve train components during operation.

VALVE TRAIN: The components or train of parts used to operate the valves in conjunction with the cams.