Camshaft and Follower Fundamentals Flashcards
Camshaft
Is a shaft with a series of eccentrics or lobes that control the opening and closing of valves
Camshaft motion transfer
Changes rotary motion into reciprocating motion
Camshaft nose
Usually the front of the shaft, a mounting surface for the camshaft drive gear or sprocket
Camshaft journals
The load bearing surfaces that support the cam in cylinder block or head
Camshaft lobes
The eccentrics that convert rotary motion into reciprocating motion of the cam follow
Valve lobe profiles
usually higher point with a shorter effective duration, will vary in shape depending on engine horsepower, speed of operation and air induction of engine
Injector lobe profiles
Usually shorter with a longer duration, vary depending on the design and requirements of the fuel injection system
Cam lobe nose
The very top of the camshaft travel and is the point of maximum lift
Cam lobe ramp (flank)
is the slope that the cam follower rides up and down on as the camshaft rotates
Cam lobe base circle
base diameter of the lobe, at this point there is no valve opening
Cam lobe lift
The distance the cam follower moves up as the shaft rotates
Cam lobe duration
The number of degrees between the point where the valve opens and the point where the valve closes.
Is measured in crankshaft degrees
Normally different for intake and exhaust valves
Camshafts are manufactured in one of 3 ways
Casting
Machined or forged from an alloy steel billet
Assembled from components
Where are cast camshaft used?
Most commonly used in low horsepower, light and medium duty diesel engines
What are two common camshaft locations
In-block
Overhead
Overhead valve engines (OHV)
Engines with the camshaft in the cylinder block and the valves in the cylinder head
Cam in-block
Camshaft motion is transmitted through the cam followers and pushrod to the rocker arm, the rocker pivots on a shaft and transmits cams motion to the valve
Camshaft bearings - Bushings
bushings that are retained by a press fit in the cylinder block cam bores
Cam lubrication
Bearings are lubricated through galleries on the block to bearings, lobes are also lubricated by splash off of the valve operating mechanism
3 basic types of cam followers
Solid
Roller
Hydraulic
Solid type cam lifters
form a solid link between the cam lobe and the valve operating mechanism. Straight body and mushroom type are two types of solid lifters. Mushroom type built to handle higher contact pressure
Roller type cam lifter
either be solid or hydraulic design. Rather then being flat bottomed, bottom is equipped with a wheel or roller
3 advantages of roller type lifters
Reduce frictional losses in the engine
Can handle much higher operating loads
Allow a quicker rate of valve opening and closing than solid type followers
Camshaft drive
Gear drive is the most common, gears may be helical or spur-cut and are usually made of cast or forged steel. usually either bolted or pressed onto the front of the cam and indexed by and keyway of dowel
Lobe separation angle
the offset between the centrelines of the intake and exhaust valves
Incorrect camshaft timing will result in:
Altered valve opening and closing points
Poor engine performance
Damage to engine components
Alter fuel infection timing on cam actuated injectors
Camshaft gear may serve as a drive for other engine accessories such as:
Fuel injection pump
Fuel transfer pump
Oil pump
Tachometer
Why would a camshaft be assembled from components or in sections?
Permit ease of manufacturing and service
Engines with cams in the block require what to transfer force from cam follower to the rocker arm?
Pushrod(s)
To control endplay, most diesel engines camshafts utilize a_______ or ________?
Thrust plate
Washer
Valve clearance is necessary with solid type follower to:
Allow for expansion of components as engine temperature increases
