Engine Variable valve Actuating Mechanisms | Valve Train System and Components | Variable Valve Timing Technologies

Valve Actuating Mechanisms:

01- Engine valve actuating mechanism - Valve lifting mechanisms

Each valve must open at the proper time, stay open for the required length of time and close at the proper time. Hence the timing of the valves are controlled by valve actuating mechanisms. Intake valves are just open before the piston reaches the Top Dead Centre (TDC), and exhaust valve remain open after TDC. At this particular instant both valves are open at the same time. This overlap results in better volumetric efficiency and lower operating temperatures.

01-Engine Valve lifting Mechanisms

  • Mechanisms with side camshaft
    • Double row side valve (T-Head) type
    • Single row side valve (L-Head) type
    • Overhead inlet and side exhaust valve (F-Head) type
    • Single row overhead valve (I-Head) type

01-Side camshaft

  • Mechanisms with overhead camshaft
    • With inverted bucket type follower operated by single camshaft
    • With end-pivoted rocker arm operated by single camshaft
    • Inlet valve operated by inverted bucket type follower and exhaust valve by pivoted rocker arm (Double camshaft)
    • Double overhead camshaft with inverted bucket type followers
    • Double overhead camshaft with separate rocker arms

01-Overhead camshaft - SOHC

Valve Train Components:

01- Engine Valve Train

  • Camshaft
  • Camshaft drive
    • Chain drive
    • Gear drive
    • Toothed belt
  • Valve tappet
    • Solid Lifters
    • Roller lifters
    • Hydraulic lifters
    • Followers
  • Push rod
  • Rocker arm and rocker shaft


A Shaft with a cam for each intake and exhaust valve. Each cam has a high spot called cam-lobe which controls the valve opening. Camshaft actually controls rotary motion to reciprocating motion.


Camshaft drive:

Cam gear is twice as large as crank gear. This makes the cam turn at 1/2 the speed of the crank

01-cam shaft drives

Valve Tappets:

The tappet follows the cam lobe and pushes the push rod. Solid and Roller lifts require adjustable rocker arm. Hydraulic Tappet requires oil to control.

01-valve tappet - valve lifters - Engine valve timing

Push Rods:

Metal rod which transfers force from the lifter to the rocker arm

01-valve push rods

Rocker Arm:

Rocker arm transmit the forces of the pushrod to the valve

01 - Rocker arm  - Engine Valve train Mechanisms

Variable Valve Timing (VVT) technologies:

VVT is an engine technology which allows the lift or duration or timing (some or all) of the intake or exhaust valves to be changed during the engine operation

  • Phase changing systems
  • Profile switching systems
  • Variable event timing systems
  • Variable lift systems
  • Electronic valve actuating systems

VVTi Engines:

VVTi system is a cam phasing system that can be applied on both inlet and exhaust cam shafts. This movement is controlled by engine management system according to need and actuated by hydraulic valve gears.

01-VVTi Engine

VTEC Engines:

VTEC stands for Valve Timing Electronic Control, where the system set the optimum valve timing by continuous changing of timing to open or close in Intake and Exhaust valves in response to the engine load, rotation and other operating conditions. This system controls the emission of NOx and HC and the fuel economy is increased.

01-VTEC Engine

01-VTEC animation


iVTEC stands for Intelligent VTEC. Honda implement this most successful valve actuation system by continuously variable intake valve timing and computer controlled management for optimized torque output and fuel efficiency.


AVTEC stands for Advanced VTEC. Honda implement this continuously variable phase control system to respond to the drivers power needs independent of engine speed. This system presents 13% better fuel economy and 75% lower emissions than iVTEC.

FIAT Multi – Air Technology:

A new engine air management technology introduced by FIAT which is much better than any VVT technology

01- FIAT multi air valve lifting technology

01- working principle of FIAT multiair valve timing technology better than VTEC

Valve Troubles:

  • Burning of valve face
  • Necking of valve stem
  • Valve face wear
  • Valve stem and guide wear
  • Valve cracking or Breakage
  • Noisy valve operation

Induction Brazing | Furnace Brazing | Copper Brazing Torch | Laser Brazing Process

There are numerous brazing methods are available. Some of them are Induction Brazing,  Furnace Brazing, copper brazing torch, infrared brazing, laser brazing, dip brazing, resistance brazing.

Brazing process steps:

Step 1: Both joints are cleaned (not polished) and fluxed

Step 2: A heat (about 450° C) is applied to the base metal, were the filler metal is melted. Excess heat burn the fluxes. So we have to repeat the process again.

Step 3: Filler metal is applied to the joint

Step 4: Filler metal adheres to both the surfaces forming a bead

Various classifications of Brazing’s are:


Hand Torch brazing:

In torch brazing, flux is applied to the part surfaces and a torch is used to direct a flame against the work in the surrounding area of the joint. A reducing flame is typically used to inhibit oxidation. After the work piece joint areas have been heated to a suitable temperature, filler wire is added to the joint, usually in wire or rod form. Fuels used in torch brazing include acetylene, propane and other gases with air or oxygen.

Furnace brazing:

Furnace brazing uses a furnace to supply heat for brazing and is best suited to medium and high production. In medium production (usually in batches), the components and brazing metal are loaded into furnace, heated to brazing temperature and then cooled and removed.

Induction brazing:

Induction brazing utilized heat from electrical resistance to a high frequency current induced in the work. The parts are pre-loaded with filler metal and placed in a high frequency AC field. The parts do not directly contact the induction coils. Frequency ranges from 5 kHz to 5 Mhz.

Resistance brazing:

Heat to melt the filler metal in resistance brazing is obtained by resistance to the flow of electrical current through the parts. As distinguished from induction brazing, the parts are directly connected to the electrical circuit in resistance brazing. The equipment is similar to that used in induction welding, except that a lower power level is required for brazing.

Dip brazing:

In dip brazing, either a molten salt bath or a molten bath accomplishes heating. In both methods, assembled parts are immersed in the baths contained in a heating pot. Solidification occurs when the parts are removed from the bath.

Infrared brazing:

Infrared brazing uses heat from a high intensity infrared lamp. Some IR lamps are capable of generating up to 5000 W of radiant heat energy, which can be directed at the work-piece for brazing.