Advertised Duration: The actual valve opening and valve closing period, taken from a theoretical point when valve leaves and regains the seat.

Area Under the Curve: The area the curve envelopes when lift and duration are plotted on a graph, two cams have the same duration and lift but the area will be greater.

Base Circle: Also referred to as the heel, and is the round portion of the camshaft where the tappet settings are made.

Base Circle run out: This is the most common problem faced in the camshaft area . The base circle must be within 0.0015" on any hydraulic cam. If the run out is over his engine will not idle on all cylinders.

Billet Cam: This is the term for a camshaft made from a solid piece of cast iron or steel bar. 99% of steel camshafts are made this way.

Boost: The amount of pressured air forced into the engine by mechanical means, measured in lbs per sq. in. or by a barometer in inches of mercury. One inch of mercury is equal to 2lbs per sq. inch and atmosphere is equal to approximately 14.7lbs per sq. inch.

Castings: This is the term used for a new camshaft. Most new cast iron camshafts start life out as a casting not as a billet. Ivan Tighe Engineering have the facilities to make new ones off billet cams for special applications.

Camshaft Follower: Usually a radiused, flat faced or roller bearing, running directly on the cam lobe, transferring the action of the camshaft to the rest of the valve train.

Camshaft Master: This is a precision template or master which is used to grind the lobe shape on camshafts. For each different profile, a different master is required.

Cam profile: The actual shape of the camshaft lobe. At Ivan Tighe Engineering these profiles are generated by computer or by mechanical method.

Clearance Ramps: The start and finish of the profile shape. This is the slow constant lift section (.00035" - .00055") per degree of cam rotation. The reason for this is to compensate for small deflections and take up the slack in the valve train.

Coil Bind: A valve spring that has been compressed to the pint that the coils are stacked solid, preventing any further downward movement.

Core: The term used for a camshaft that is used on an exchange basis. A core is required if a regrind camshaft is supplied.

Damper: This is the term used for the flat spring used in some single or dual spring applications. The flat spring allows a more complex spring for valve control without raising the spring tension considerably.

Differential Angle: The difference between the angle of cylinder centre line and the angle of the cam follower centre line. Most commonly found in V6 and V8 engines and in rare 4 cylinder engines.

Desmodromic: A complex type of valve gear where each valve is operated by two lobes. One lobe opens using a normal rocker and the other closes using a reverse rocker to close the valve. No valve springs are required to control valve motion.

Duration: The amount of time in degrees that the valves are off their seats during the opening period of the cam.

Duration = opening degree + closing degree + 180 deg

Fitted Dimension: Referring to the valve spring. This is the height of the fitted spring when the valve is closed. Measured from the cylinder head to the seat of the spring retainer (also known as installed height).

Flame Hardening: This is a hardening technique using oxy/acetylene torch
to heat a camshaft to a cherry red which is then quenched in a water based coolant.

Flank: The side of the cam lobe that lies between the nose and the base circle. This is the area that most wear occurs.

Gear Drive: This gives precision perfect cam timing and eliminates cam and distributor timing errors or changes due to wear or chain stretch.

Gross Lift: The theoretical valve lift obtained by multiplying the cam lift by the rocker arm ratio. This does not take into consideration the tappet setting.

Hardfacing: This is the process used to build up O.H.C. type and most motor cycle camshafts. The original profile is ground back and a layer is placed over the top - the camshaft is then trimmed and finish ground.

Heel: Same as the "Base Circle" - the concentric part of the cam lobe where the tappet settings are made.

Induction Hardening: An electrical process of heat treating, where a camshaft is passed through a coil, through which a high frequency current is passed. The camshaft inside the coil is quickly heated to a cherry red and quenched in oil. Ivan Tighe Engineering hardens all new camshafts using this process.

Inner Valve Spring: This refers to the smaller valve spring used inside the standard single type spring. The advantage of the inner spring is lighter seat tension cam still obtain high nose pressure, giving better valve control.

Interference Fit: This term is used in reference to valve springs. The inner spring is a very tight or push fit in the outer spring. This allows lower spring tension to be used. This type of spring requires lots of lubrication or spring breakage may occur.

Lash Caps: A small cap placed on top of the valve to give the hydraulic lifter more preload. Available for 9/32, 11/32, 3/8 and 8mm valve stems.

Lobe Centers: This it the angle between the inlet or exhaust lobe on the one cylinder and the Top Dead Center position when the camshaft is in the engine. Measured in degrees and normally between 95deg and 120deg the inlet is measured after T.D.C. - exhaust is measured before T.D.C.

Lobe Center Calculation: Inlet: op. deg + cl. deg /2 - op. deg = lobe center line
Exhaust: op. deg + cl. deg /2 - cl. deg = lobe centre line

Lifter: See "Cam Follower".

Lubriteing: This is the black coating on all the cast iron camshafts. It is simply an anti scruff coating so as to stop metal to metal contact on initial start up. The process is applied at approximately 100deg c and uses a combination of phosphor and graphite. Contrary to popular belief it has no effect on hardness at all. Also sometimes called Parkerising.

Mushroom Lifter: This is a flat type lifter that has the head of the lifter a larger diameter that the body of the lifter. These are standard equipment in some 4cyl. Engines, but are fitted in some races engines to allow profiles with very rates of lift (very high lift with short duration)

Nett Lift: The actual lift of the cam as measured at the valve. This can be obtained approximately by multiplying the cam lift by the rocker ratio and subtracting the tappet clearance. In an O.H.C. rocker engine this is only a guide, the actual may vary by up to .040" or more.

Normally Aspirated: An engine that has a carburettor or is fuel injected without any mechanical devise that forces air under pressure onto the combustion chamber.

Nose of Cam: The highest point of the cam lobe and often the area where most wear occurs.

Offset Bushes: These are round offsets available for pin drive camshafts, so they can be advanced and retarded without drilling other holes in the drive gears.
The drive hole in the cam gear is simply drilled to take the bushing. Available for most common pin drive cams.

Offset Key: This is a stepped key that is used to advance and retard camshafts that are driven by a key rather than a dowel.

O.H.C.: Over Head Cam type engine

Outer Valve Spring: In a double spring combination the outer spring is always the larger of the two springs. The outer is also the higher tension and should be wound in a different direction to the inner.

Overlap: The period where both inlet and exhaust valves are open at the same time - when the piston passes T.D.C. every second time. To determine the degrees of overlap add the opening of the inlet and the closing of the exhaust together from the valve timing supplied by the manufacturer.

Phase Angle: The angle between the inlet and exhaust lobe of a camshaft and is measured in degrees. This is taken as the angle on the camshaft not in the engine and is often confused with lobe centres. Can also be called lobe separation angle.

Posi Locks: These re the locking type nuts used to lock the adjustment on a studded roller rocker. A long type of nut with a grub screw so as to lock the nut on the stud.

Preload: The term used for the load that is applied to the hydraulic lifters during engine assembly. A lifter requires at least 0.010" preload so not to rattle.

Pre-lube: A molly based grease that is supplied in the box with all new camshafts. It is used to coat the lobes when fitting the cam to eliminate the possibility of lobe failure at the critical start period.

Ramps: This is the slow acceleration section at the start and finish of most camshafts profiles. For solid cams the ramps may be as long as 15deg and 0.020" - for hydraulic cams this must be below 0.006" for the cam to function.

Ramp Height: This is the height from the base circle to the top of the ramp of the cam profile. The advertised valve timing is taken at the top of the ramps. The tappet settings are also determined by the ramp height.

e.g. .020" ramp height 1.5:1 rocker ration
Tappet setting = (0.020" x 11.5) minus 0.001"
= 0.029" (Normal tappet setting)

Regrind: Term used when a worn camshaft is reprofiled to the same profile or modified to a different profile. To achieve this the bulk of the shaft may need undercutting to keep the base circle above the shaft diameter.

Rockwell Hardness: The type of hardness testing used to check the hardness of most hardened materials. Rockwell C process uses 120deg diamond with a weight of 150kg. of preload on it. This is loaded into material, and depth of the indent is measured . The result of this is given in a Rockwell C measurement.

e.g. A cast iron cam is approximately 56r/c
A steel roller cam is approximately 60r/c

Solids: This term is used in reference to solid cam followers - the hydraulic section of the lifter is replaced by solid internals.

Solid camshaft: If hydraulic followers are replaced by solid followers the camshaft profile must be changed so as to suit the solid followers.

Split Overlap: This occurs on the overlap stroke when inlet and exhaust valves are open the same amount at the same time. If the camshaft being used has the same profile on both lobes, split overlap will indicate that the cam is in square in the engine (neither advanced or retarded).

Spring Fatigue: The tremendous heat generated by continual stressing of the valve spring will eventually cause it to sag or fatigue, A valve spring will settle approximately 10% as soon as fitted.

Spring Height: See Installed Height

Spring Pressure: The force exerted by the spring on the valve to keep the valve following the camshaft profile correctly.

Spring Retainer: This is a stepped type washer that located the top of the valve spring on to the top of the valve. Can be made if steel, aluminium or titanium. Stepped retainers also available to extend spring installed height.

Steel Billet: A solid piece of steel bar stock that is made into a camshaft. Ivan Tighe Engineering machine their roller type camshafts in this manner.

Super Charged: A driven pump that forces air into the engine. This type use engine power to turn the supercharger and the impellers can be centrifugal, roots or vane type.

Tappett Setting: The valve clearance that the cam profile requires to be set at to achieve best working conditions. This is required to allow for thermal expansion.

Valve Bounce: this occurs when the engine is revved higher that the valve springs will permit. The valve will no longer follow the cam profile and will crash back onto the valve seat. This will cause loss of power and , if prolonged, will cause valve failure, shorten camshaft/ lifter life and cause considerable damage to engine components.

Valve Train: The components or parts used to operate the valves in conjunction with the camshaft.