GLOSSARY OF CAMSHAFT TERMS

You know you do not need to know anything about cams to buy a camshaft and valve train components from Kustom Bitz, just follow our recommendations on matching parts and pay attention to what we say about how the cam will behave.  However it can be handy and real interesting if you do learn the camshaft terms and what they mean. If you learn them well you will easily pick up when your mates are talking rubbish and isn’t that good?

Advanced: The camshaft timing is advanced. Usually done with the timing gears or timing chain. Advancing the cam can make the cam appear a little smaller to any given engine. Advancing the cam makes the peak cylinder pressures [bmep] occur earlier in the rpm range. Advancing the cam shifts the optimum operating rpm range [power band] lower. Some camshafts are ground with advance built into them. Advanced cams can be real torquey in the lower rpm range.

Advertised Duration: The actual valve opening and valve closing period, taken from a theoretical point when valve leaves and regains the seat. Also referred to as the total duration, usually taken from 0.002-0.005 thou lift.

Anti-Pump Up Lifters: Standard OEM Hydraulic lifters are constructed in a manner that they pump up. That is as oil pressure builds up in the cushioning effect of the plunger inside the lifter so they pump up to a hardness that prevents the lifter bleeding down at low rpm and when the engine is stopped. This is fine for short duration low lift OEM cams however on longer duration higher lift performance cams this pump up effect can hold the valve of its seat in the higher rpm ranges, combine this with a high volume pump and you might have troubles. Anti-pump up liters or high rev lifters are designed so that they do not hold oil pressure and pump up and cause detrimental problems for your performance engine, hence they are noisier on start up and have a slight tickety ~ tick sound when running.

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.

A.B.D.C. After Bottom Dead Centre, referring to the piston in the cylinder bore relative to crankshaft rotation.

A.T.D.C. After Top Dead Centre, referring to the piston in the cylinder bore relative to crankshaft rotation.

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.

B.D.C. Bottom Dead Centre, referring to the piston in the cylinder bore relative to crankshaft rotation.

B.T.D.C. Before Top Dead Centre, referring to the piston in the cylinder bore relative to crankshaft rotation.

B.B.D.C. Before Bottom Dead Centre, referring to the piston in the cylinder bore relative to crankshaft rotation.

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 un-machined camshaft.

Camshaft Follower: A radius based, 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 Dowel: this is the pin that engages the timing gear or timing chain so that the camshaft turns in time with the crankshaft.

Cam profile: The actual shape of the camshaft lobe.

Checking Springs: Light gauge valve springs used only during engine assembly to check piston to valve clearances and to degree in the cam.

Clearance Ramps: The start and finish of the profile shape referring to the slow constant lift section in the initial .00035 - .00055 thou per degree of cam rotation. The clearance ramps up the slack in the valve train  and compensate for small deflections.

Coil Bind: A valve spring that has been compressed to the point that the coils are touching and preventing any further downward movement.

Collets: usually two per valve to hold the spring retainer in place when the spring is installed.  The pairs form a ‘V’ shape at the top of the valve stem and the spring pushing up on the retainer forces them into a groove in the valve stem, hence holding the retainer and spring in place. It is important to have grooved collets that match the grooves in the valve stem. You also have to match the collets ‘V’ measured in degrees so they are the same as the retainer.

Core: The term used for a camshaft that is used on an exchange basis for example when regrinding a camshaft.

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.

Detonation: Engine Detonation is also referred to as engine ping or pigging. This phenomenon is the fuel igniting as the piston is still on its way up the cylinder bore. The crank is rotating quickly with the connecting rod pushing the piston up so the piston has no where to go but up yet the pressures of the early ignition force the piston to rattle on the cylinder walls and that is what you can hear from the drivers seat. Not all detonation can be heard. Detonation can lead to piston fatigue and the piston falling apart and causing catastrophic engine failure. Also known as Pre-Ignition.

Degree Wheel: Installed on the crankshaft temporarily during the engine build to degree the cam in and check for correct valve timing events.

Degreeing: Degree the Cam in. This is the work you do of checking the valve opening and closing events to check that the cam is installed correctly in the engine. You are checking the valve timing events when you do this.

Differential Angle: The difference between the angle of cylinder centre line and the angle of the cam follower centre line. Most commonly found in V configuration engines like V6 and V8 engines. However this geometry is rare in straight six and 4 cylinder engines.

Duration: The amount of time in degrees that the valves are off their seats during the opening period of the cam. To calculate total duration take the opening degree plus the closing degree then add 180 deg.

Duration @ 50: More correctly said as duration at .050 thou lift - is the duration of the cam profile measured from .050 thousands of an inch opening lift, to the closing event at 0.050 thousands of an inch. This figure is the figure that tells you more about the camshafts characteristics, ie. How it is going to behave in an engine rather than looking at the total duration. This is mainly because up until .050 lift there is not much happening in the ports at all.  If you want to compare camshafts then compare their duration @ 50 figures to see if they are similar.

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 valve opening distance obtained by multiplying the cam lift by the rocker arm ratio. This does not take into valve lash on solid lifter camshafts.

Hard facing: 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.

Ignition: All components that create the spark to occur at the right time within the engine.

Ignition timing: The variable time that the spark occurs with reference to crankshaft rotation in degrees.

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.

Inner Valve Spring: This refers to the smaller valve spring used inside the standard single type spring. The advantage of an inner spring is lighter seat tension on the camshaft yet still obtain a high nose pressure, to give better valve control on high lift race cams.

Installed Straight Up: the camshaft is installed on the standard corresponding timing gear/chain marks to the crankshaft. It is not installed advance or retarded.

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: Is the tear drop shaped part of the cam shaft that the cam follower runs around. More commonly referred to as the lumpy shaped part. Hence the term Lumpy cam, real hot cams have bigger lumps.

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 lobe center line = open degrees + closed degrees divided by 2 then subtract the open degrees Exhaust lobe center line = open degrees + closed degrees divided by 2 then subtract the closed deg = lobe centre line

Lobe Separation Angle: Or phase angle, is the angle from the inlet lobe centre to the corresponding Exhaust lobe centre. Some times Lobe centers are confused with this term by some people. However the lobe separation angle can tell you more about a camshafts characteristic than anything else.

Lifter: A radius based, flat faced or roller bearing, running directly on the cam lobe, transferring the action of the camshaft to the rest of the valve train. Also referred to as “Cam followers”

Lift: Generally used loose term refers to follower movement at the camshaft – “camshaft lift” or “Lift at the Cam” and Valve opening amount “Lift at the Valve”

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 high rates of lift and 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 carburetor or is fuel injected without any mechanical device like a blower, supercharger or turbo charger 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.

Pinging: Engine Ping, engine knock, see detonation.

Piston to Valve Clearance: A physical check of how much clearance there is from the top of the piston to the valves when all the engine is installed. This requires engine assembly and disassembly to check. It is a very important and necessary check for any newly built engine. Usually the exhaust valve is the most critical because the piston chases the valve closed as the exhaust gases are expired from the cylinder.

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 centers. Also referred to as the 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.

Pre-Ignition: see Detonation.

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. Typically this is ½ to ¾ turn on the adjusting nut that either holds the rocker arm on the stud or an adjuster on the rocker arm at the pushrod end.

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. NOTE: liberally cote the lobes and under the base of the lifter but use sparingly within your new engine so as you do not create issues with the piston rings not bedding in.

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 rationTappet setting = (0.020" x 11.5) minus 0.001"= 0.029" (Normal tappet setting)

Regrind: Term used when a worn camshaft is re-profiled to the same profile or modified to a different profile. Some cams may require the bulk of the shaft to be undercut to keep the base circle above the shaft diameter. Note usually reground cams have limits on the amount of lift you can achieve because of the physical lack of material to create the valve opening distance.  That is why most performance cams are new billets.

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

Retard: Retarded the camshaft timing is retarded. Usually done with the timing gears or timing chain. Retarding the cam makes the peak cylinder pressures [bmep] occur later in the rpm range. Retarding the cam shifts the optimum operating rpm range [power band] higher. Generally speaking you want to avoid retarded cam timing because the engine will feel real sluggish. Note that late 1970’s and 1980’s carburetor pollution controlled engines used retarded cam and ignition timing to promote full burn in the combustion chamber to meet emissions requirements. Also at the expense of much lower horsepower and torque.

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/cA 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. Therefore there is no pre-load on a solid lifter camshaft, instead you have a valve lash adjustment which is typically .020 to .030 thou.

Solid camshaft: If hydraulic followers are replaced by solid followers the camshaft profile must be changed so as to suit the solid followers.  Solid lifter cams are higher in maintenance because you have to adjust the valve lash as the engine wares. Typically solid cams are race only cams and produce incredible power and torque for mid range acceleration.  The sportsman drag racers you see in groups 2 and 3 adjusting valve lash between rounds and checking spring pressures have their engines dialed in on that tight edge of making power that wear is an issue and continual checking ensures they can consistently make the same power run after run and run on their dial in, and the engine lives through each round.

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. It can be made from 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. High end roller type camshafts can be made 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.

Tappet 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, more typical on solid lifter cams. Also known as valve lash adjustment.

T.D.C. Top Dead Centre, referring to the piston in the cylinder bore relative to crankshaft rotation.

Total Duration: is the total time that the valve is open, usually specified from .005 lift.

Valve: The engine part that allows fuel to enter the cylinder for compressing and another valve allows the spent gasses to escape after being compressed and ignited.

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 as the lobe flips over after lifting. This will cause loss of power because the valve then bounces like a bouncing ball, it oscillates, hence no sealing of the cylinder for compression at TDC. If prolonged, valve bounce will cause valve failure, shorten camshaft/ lifter life and cause considerable damage to engine components. Hence it is important to use matched or recommended valve springs for a particular camshaft. As a rule of thumb ….. ‘standard OEM springs are good for nothing ……. not even for a towing cam’.

Valve Lash: 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, more typical on solid lifter cams. Also known as Tappet Setting.

Valve Spring: Holds the valve closed and maintains appropriate pressure within the valve train to ensure matched components can cope with the lobe profile of that particular camshaft.

Valve Timing: The valve timing is the opening and closing of the inlet and exhaust valve with relation to the rotation of the crankshaft. The valve timing is set with the timing gears, the duration and lift is built into the camshaft. Typically given in degrees. Also referred loosely to Valve Events, however to be correct ….. you install the timing chain to give you the correct valve events for the opening and closing of the valve to the cam’s intended performance specifications.

Valve Train: The components or parts used to operate the valves in conjunction with the camshaft. Can include parts like the timing chain, valve springs, lifters, rocker arms, rocker arm studs, push rods, etc.