This article explains camshaft, lifter, tappet and follower configurations
present in the automotive industry.
Overhead Camshaft Configuration
- A lifter is located either in the engine
block or cylinder head, and is controlled by oil pressure supplied by the oil pump.
This overhead camshaft configuration uses a lifter and a roller follower to push
against the valve spring to open the valve, either intake or exhaust.
Overhead Camshaft Lifter Follower (Cutaway Cylinder Head)
Step 2 - The lifter provides the automatic adjustment
(In older engines, valve lash must be adjusted by hand) which is supplied by oil
pressure. When the lifter is forced away from the camshaft by rotation, the oil
valve inside the lifter is closed which traps the oil inside the lifter while opening
the valve. The follower then transmits the force to the valve stem.
Step 3 - Although this follower is designed with
a roller, some simply ride against the camshaft without a roller.
- As in all hydraulic lifter configurations,
engine oil pressure is used to lubricate and pressurize the lifter plunger.
Camshaft In Block
Step 5 - The alternative design to overhead valve
train construction is the in block camshaft, (IBC) this design is traditionally
an older design and less efficient than its counterpart due to the added weight
of the additional components such as a push rod and full rocker arm which required
a heavier valve spring.
Lifter Oil Passage (Cutaway)
Step 6 - From the topside of the block, the lifter
rides inside the lifter bore which is located underneath the intake manifold. From
the lifter, a push rod is used to actuate the rocker arm which activates the valve
spring that is located on the cylinder head.
Camshaft In Block (Bottom)
A cylindrical rod is situated in the cylinder block or cylinder head which has
oblong lobes or cams which push the intake and exhaust valves. This force is applied
on the valve directly or through an intermediate mechanism such as a rocker arm,
lifter (cam follower) and push rods are used to press against the valve for movement.
Camshaft to crankshaft correlation timing is adjusted by the
Lifter In Block
There are two kinds of camshaft, lifter-tappet, follower configurations used
in the automotive industry: IBC (In Block Camshaft) and OHC (Overhead Cam). IBC
has been used since the early years of the automotive industry. This type of configuration
uses a centrally located camshaft (in block) with lifters and push rods that open
and close the valves in the cylinder head(s).
Lifters follow the camshaft lobes which dictate how far the valves open (lift),
and how long they stay open (duration). Lifters come in different configurations
such as; solid, hydraulic, roller, mushroom, all of which work on the same principle.
Solid lifters have no hydraulic adjustment and rely on the valve lash (air gap)
to be manually set at the stem of the valve where it contacts the rocker arm. Solid
lifters are used mostly in racing applications where higher engine rpm and long
duration can damage normal hydraulic lifters.
Roller lifters are exactly as the name implies, they are designed with a roller
wheel and needle bearings that ride along the camshaft. These lifters reduce drag
caused by friction and are found in most production vehicles.
When a lifter fails it can cause an engine misfire and cause abnormal noises,
this unusually occurs when the valve inside the lifter is leaking and fails to hold
Article first published 2016-02-03