Home ยป Tools

The Rover V8 and Buick 215 Engine Cam Terminology

  • ABDC:
  • Degrees after bottom dead center.
  • ATDC:
  • Degrees after top dead center.
  • BBDC:
  • Degrees before bottom dead center.
  • BTDC:
  • Degrees before top dead center.
  • BASE CIRCLE:
  • The concentric or round portion of the cam lobe where the valve lash adjustments must be made. (Also known as the heel.)
  • CAM FOLLOWER/TAPPET:
  • Usually a flat faced or roller companion to the camshaft that transfers the action of the camshaft to the rest of the valve train by sliding or rolling on the cam lobe surface.
  • CAM LIFT:
  • This is the maximum distance that the cam pushes the follower when the valve is open. This is different from valve lift. See GROSS VALVE LIFT."
  • CAM PROFILE:
  • The actual shape of the cam lobe.
  • CAMSHAFT:
  • A shaft containing many cams that covert rotary motion to reciprocating (lifting) motion. For every 2 revolutions of the crankshaft, the camshaft rotates 1 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.
  • 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 at when this happens.
  • CONCENTRIC:
  • Running true or having the same center. 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.
  •  DURATION AT .050":
  • The amount of time measured in degrees of crankshaft rotation from when the valve is open .050" far until it is .050" from closing.
  • FLANKS:
  • The sides of the cam lobe or the portion of the lobe that lies between the nose and the base circle on either side.
  • GROSS VALVE LIFT:
  • This is obtained by multiplying the cam lift by the rocker arm ratio.
  • HYDRAULIC VALVE LIFTERS:
  • These lifters are designed to maintain zero lash in the valve train mechanism. Their advantages include quieter engine operation and elimination of the periodic adjustment required to maintain proper lash as with solid valve lifters. Hydraulic lifters do, however, maintain a constant pressure on the camshaft, which solid lifters do not; therefore, the antiscuff properties of lubricating oils are more critical with hydraulic lifters.
  •  IMPROVED STOCK CAMS (CHEATER CAMS):
  • The improved stock cam has stock lift and duration 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 FAQ's systems that run off of manifold vacuum and are therefore very sensitive to camshaft duration changes.
  • 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.
  •  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):
  • This is the clearance between the base circle of the camshaft lobe and the camshaft follower or tappet.
  •  LIFT GRAPH:
  • By installing the camshaft in a block or head, the mechanic can plot the lift of the cam in relation to each degree of camshaft rotation by installing a dial indicator on the cam follower or tappet and a degree wheel on the crankshaft. All that is necessary is to rotate the crankshaft every 5 degrees and take a reading on the dial indicator at each of these intervals and transfer the readings to the graph paper.
  • 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. (i.e. street use or all out competition).
  •  LOBE CENTERS-CAM:
  • The distance measured in degrees between the centerline of the intake lobe and the centerline of the exhaust lobe in the same cylinder.
  • 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 F 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 .010" 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.
  • OHV (PUSHROD ENGINES):
  • Overhead valve engines. In this type of engine the camshaft is positioned beneath the valves. (i.e. Rover V8 engine)
  • OVERLAP:
  • A situation where both the intake and exhaust valves are open at the same time when the piston is at top dead center on the exhaust stroke. The greater the seat duration is on the intake and exhaust lobes, the greater the overlap will be in degrees.
  •  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 in degrees of crankshaft rotation that the valve is off of its valve seat from when it opens until when it closes.
  • 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 50 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).