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iTrader: (2)

I DIDNT WRITE THIS but thought it might be helpfull <img src="https://ls1tech.com/threads/images/graemlins/smirk.gif" alt="" />


This Cam Glossary was created by Elgin Cams to help provide our clients a tool which they can in turn use to decipher all the cryptic acronyms used in the cam grinding industry. Hope you find it useful.

ABDC:
Degrees after bottom dead center.
ATDC:
Degrees after top dead center.
AREA UNDER THE CAM LIFT CURVE:
The area under the bell shaped curve with lift on the vertical axis and degrees of rotation on the horizontal axis. The greater the area under the lift curve, the greater is the lift and/or duration at some point on the camshaft profile.
BASE CIRCLE:
The concentric or round portion of the cam lobe where the valve lash adjustments must be made. (Also known as the heel.)
BBDC:
Degrees before bottom dead center.
BTDC:
Degrees before top dead center.
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 MASTER:
After the design of the cam is computed, it is transferred to a percision 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 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.
CARBURIZING:
Gas carburizing is a method to heat treat steel camshaft billets. In this method, the camshaft is placed in a carbon gas atmosphere furnace and heated to the proper temperature. When the shaft has absorbed the proper amount of carbon, it is removed from the furnace and quenched to the proper temper.
CAST BILLET:
A term used to describe a camshaft which is made from a casting. The material for the casting is a special grade of iron alloy called "Proferal." GLOSSARY OF CAMSHAFT TERMS (CONTINUED)
CHEATER CAMS:
See "Improved Stock Cams".
CHILLED IRON LIFTER:
A cam follower made from high quality iron alloy that is heat treated by pouring the molten iron into a honeycomb mold with a chilled steel plate at the bottom to heat treat the face of the lifter. It is compatible with steel and hardface overlay cams only.
CLEARANCE RAMPS:
The portion of the cam lobe adjacent to the base circle which lifts at a constant slow speed. It's purpose, in theory, is to compensate for small deflections and take up the slack in the valve train created by the valve lash. The opening ramp takes up all clearances in the valve train and causes the valve to be on the verge of opening. The closing ramp begins when the valve touches the valve seat and ends when the tappet returns to the base circle. 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 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.
FLAME HARDENING:
A heat treating process whereby a camshaft is exposed to an open flame and then quenched (cooled in oil).
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. Rocker arm production tolerences can vary this figure by as much as +/- .015".
HARDENABLE IRON LIFTERS:
A cam follower made from high quality iron alloy. This special alloy is compatible with cast iron billet camshafts. The entire body of the hardenable iron lifter is hard as compared to the chilled iron lifter where only the base is hardened.
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 fuel injection 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.
LIFTER PRINT (CAM PRINT):
The amount of travel the cam lobe has across the lifter face. Lifter diameter determines flank velocity.
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.
LOBE CENTERLINES-VALVE:
The point at which the valve is fully open. For example, full intake lobe lift at 110 deg. ATDC. full exhaust lobe lift at 110 deg. BTDC. This camshaft was ground with 110 deg. lobe centers and is timed straight up. It is neither advanced or retarded. Another example, full intake lobe lift at 105 deg. ATDC. full exhaust lobe lift at 115 deg. BTDC. This camshaft was ground also on 110 deg. lobe centers but is advanced 5 crankshaft degrees.
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 (TL). If the back side of the lobe is greater than the front side then we say that the cam has taper right (TR). 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 subtracting the valve lash dimension from the gross valve lift figure. Rocker arm production tolerences can vary this figure by much as +/-.015".
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.
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 engine the camshaft is positioned above the valves. (i.e. Porsche 944 engine)
OHV (PUSHROD ENGINES):
Overhead valve engines. In this type of engine the camshaft is positioned beneath the valves. (i.e. 350 c.i. Chevrolet 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.
PARKERIZING:
A thermo-chemical application whereby a nonmetallic, oil-absorptive coating is applied to the outside surface of the camshaft. This permits rapid break-in without scuffing the cam lobes.
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 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.
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).
SPRING SURGE:
The factor which causes unpredictable valve spring behavior at high reciprocating frequencies. It's caused by the inerita 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.



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iTrader: (16)

damn, talk about brought back from the depths. good info though.

Clipper

Thank you so much! Great info. Now, does anyone know of any similar docs explaining in detail each of the cam measurements, along with general effects associated with each measurement? I'm looking to make a very informed decision as far as a cam purchase, but I'm pretty new to cams, and don't feel the generalized "which cam is best" threads can fully apply to my sutuation and desires.