Inside an engine, there is a mechanism for controlling the valve train. The valve train contains camshafts, lifters, rockers, valves and springs. It can be either a single camshaft or a dual camshaft, depending on the engine design, usage, load conditions, number of valves and the like.

SOHC stands for Single Over Head Camshaft and DOHC stands for Dual Over Head Camshaft. Every engine is designed according for a specific purpose. A valve train should be light so that it does not possess a lot of rotational inertia. Also, a heavier valve train means that more power will be required to open and close the valve mechanism, which eats into the share of usable power, hence also affecting fuel efficiency.

The Yamaha R15`s engine uses a SOHC design while the CBR 150R uses a DOHC one.

In the SOHC design, the single camshaft is situated in the cylinder head, above the valves. 2 or 3 valve designs are the most common ones but as mentioned earlier, 4 valve designs are also available, though they are a little more complex to manufacture. SOHC engines, as you may have seen in the case of the Yamaha R15 tend to have better low end torque (off the line).

Single Over Head Camshaft

Advantages Of SOHC Setup

1) Light in weight.
2) Better acceleration.
3) Lower cost and compact size.

Disadvantages Of SOHC Setup

Spark plug cannot be placed in the central position in case of a 4 valve SOHC design, thus may lead to incomplete combustion.
In the DOHC design, both camshafts are situated in the cylinder head. As is obvious, implementing a 4 valve design is easier with the DOHC setup. Most engines with the DOHC setup are known to rev higher than their equivalent SOHC designs. This also allows a much more optimized valve setup, thus improving performance. DOHC engines have lesser torque just off the line due to their bulk but higher up the rev ranges, this becomes an advantage as they have greater peak torque as well as horsepower.
Dual Over Head Camshaft

Advantages Of DOHC Setup

1) The spark plug can be placed directly in the central position, thus giving more complete combustion characteristics.
2) More precise valve timing.
3) Can handle more valves.
4) Greater performance modification potential.
Disadvantages Of DOHC Setup

1) Bulkier setup as compared to SOHC.
2) More complexity and hence more cost.

So to sum it up, SOHC engines have better low end grunt while DOHCs have better high end power. All in all, 4 valves are much better than 2 valves per cylinder because it allows the engine to breather better, any day. However, it does not really matter whether that is achieved via SOHC or DOHC.


The milling is a machining process in which, a rotary cutter is used to remove the material from work piece in the direction perpendicular to the axis of rotation. The milling process is done by the machine, which hold both the tool and work piece in jig and fixture, known as milling machine. There are two ways to cut the material from the work piece through milling machine. First one is named as conventional milling or Up milling and the other one known as climb milling or down milling. The main and basic difference between up milling and down milling is the direction of rotation of cutter to the feed.

The milling operation is used to face those work piece, which are not symmetrical from its axis. It is also used to cut pockets, drill, slot and shape the work piece according to the requirement.

There are two ways to cut the material from the work piece through milling machine. First one is named as conventional milling or Up milling and the other one known as climb milling or down milling. The main and basic difference between up milling and down milling is the direction of rotation of cutter to the feed.

In up milling the cutter rotates clockwise when cutting the work piece from right to left. In this type of milling the tool spins against the direction of feed. In this milling process, the cutting chips are carried upward by the tool.
Difference Between Up Milling and Down Milling

In down milling, the cutter rotates clockwise while cutting the work piece from left to right. In this milling operation, the tool spins with the direction of feed. The cutting chips are carried downward by the tool.
Difference Between Up Milling and Down Milling

Difference between up milling and down milling :-

Up Milling
 Down Milling
In up milling the cutter rotates against direction of feed.
In Down milling, the cutter rotates with direction of feed.
It is also known as conventional milling.
It is also known as climb milling.
In this, chip width size is zero at initial cut and increase with feed. It is maximum at the end of feed.
In this cutting process, chip size is maximum at start of cut and decrease with the feed. It is zero at the end of feed.
In this process, heat is diffuse to the work piece which causes the change in metal properties. 
In down milling most of heat diffuse to the chip does not change the work piece properties.
In up milling, tool wear is more because the tool runs against the feed.
In this, tool wear is less compare to the up milling, due to the cutter rotate with the feed.
Tool life is low.
Tool life is high.
The cutting chips are carried upward by the tool so known as up milling. 
The chips are carried downward by the tool so known as down milling.
The cutting chips fall down in front of the cutting tool which again cut the chips cause less surface finish.
The cutting chips fall down behind the tool. This gives better surface finish.
Due to upward force by tool, high strength zig and fixture required to hold the work piece.
In down milling, downward force act on work piece normal zig and fixture required.


Spoilers are added to cars and other vehicles to make them more aerodynamic. Most are attached to the back of the vehicle, above the trunk, on the rear window, on the roof, or on the front. Various types and the positioning of a spoiler can do different things to improve a vehicle’s performance. However, the main reason people install these gadgets is to allow for better airflow over and around the vehicle, which in turn, creates better grip or traction on the road. Vehicles that run at high speeds often encounter control problems because, at high speeds, the increased airflow creates too much lift, which can be especially dangerous when the vehicle makes a turn, as this can make it fly off the road and lose control.

Benefits of a Car Spoiler :-

Installing a spoiler on a vehicle provides a variety of benefits for owners. The main benefits, perhaps, are for better traction and to add a sporty look, but also include other advantages, such as increased fuel efficiency, added visibility, reduced vehicle weight, and braking stability.


Benefit 1: Maintain Traction

The main benefit of installing a spoiler on a vehicle is to help it maintain traction at very high speeds. When a vehicle goes very fast (over 70 mph), the air pressure can lift the car, which makes it difficult to maneuver the car without the danger of having it spin out of control. Rear spoilers, in particular, push the back of the car down so the tires can grip the road better and increase stability.


Benefit 2: Increase Fuel Efficiency

Front car spoilers or air dams can increase gas mileage in some cars. Since these types of spoilers reduce the drag, instead of increasing it, by pushing the air around the vehicle, it does lower the amount of energy, or fuel, the car needs to burn to propel itself forward.

Benefit 3: Added Visibility

Another advantage of installing a rear spoiler on a vehicle is the added visibility, which means other drivers on the road can easily see the vehicle to help prevent rear-end collisions and other types of accidents. Certain spoilers, such as trunk cap spoilers, even have brake lights at eye level so the driver behind can easily be alerted when the vehicle is slowing down or braking.

Benefit 4: Reduce Weight

Believe it or not, a spoiler can reduce the weight of a vehicle. While this may seem counterintuitive, it makes sense in a way. The only thing keeping a vehicle stable on the road is its weight. Perhaps that is why many people have this perception that SUVs are much safer because their heavier mass keeps them steady. However, having a spoiler means that the car manufacturer can reduce the weight of the vehicle by using lighter materials or doing away with unnecessary weight without the worry that driving at high speeds causes the car to become unsteady and fly off the highway.

Benefit 5: Create a Stylish Look

Most car owners install spoilers as a fashion accessory, and spoilers do a pretty good job of making a vehicle look cool. This idea first became popular in the 1970s, when Porsche introduced the 911 Turbo, which featured whale tail spoilers on the back. Today, many cars come with built-in spoilers to evoke that sporty look, though many aftermarket spoilers are available for a wide variety of car makes and models.

Benefit 6: Increase Braking Stability

Adding spoilers that raise the downward force on the back of the vehicle not only increases traction, but the braking ability as well. Drivers have an easier time braking, even at high speeds, making driving even safer.


The defects in the weld can be defined as irregularities in the weld metal produced due to incorrect welding parameters or wrong welding procedures or wrong combination of filler metal and parent metal.

Weld defect may be in the form of variations from the intended weld bead shape, size and desired quality. Defects may be on the surface or inside the weld metal. Certain defects such as cracks are never tolerated but other defects may be acceptable within permissible limits. Welding defects may result into the failure of components under service condition, leading to serious accidents and causing the loss of property and sometimes also life.

1. External Defects in welding:

External defects of welding include overlap, undercut, spatter, crater, excessive convexity, excessive concavity, surface porosity, surface cracks.

1.1 Overlap:

  • Magnetic arc  blow.
  • Excessive size of electrodes.
  • Use old small welding speeds during joining of small thickness plates.
  • Excessive current conditions.

1.2 Undercut

Undercut area appears like a small notch in the weld interface.
  • Use of magnetic arc blows with direct current straight polarity.
  • Undersize electrode and insufficient current conditions etc.
  • Use of high welding speeds during joining of large thickness plates.
  • Excessive arc length.
  • Excessive side manipulation.
  • Use of damp electrodes.

1.3 Spatter:

During welding operation due to the force of arc, some of the molten metal particles are jumping from weld pool and falling into other areas of the plate is called as spatter.

  • Use of low welding speeds during joining of large thickness plates.
  • Excessive arc length.
  • Use of sample electrodes.

1.4 Crater:

  • At the end of welding in Gas Welding, a shallow spherical depression is produced known as the crater.
  • crater -This is due to improper welding technique and is formed at the end of weld run.
  • This may be remedied by proper manipulation of the electrode. when finishing a weld the operator should not draw away the arc quickly but should maintain the arc without moment until the crater is filled up.
  • On re-striking the arc, to continue the weld bead, the arc should strike approximately 15mm in front of the previous bead and travel backwards and then forward the direction of welding.
Incorrect torch angle or use of large angle at the end of the weld bead.

1.5 Excessive Convexity:

  • Use of low welding speed with direct current reverse polarity.
  • excessive current conditions.
  • Use of large size electrodes for joining of small thickness plates.

1.6 Surface Porosity:

  • Porosity is a group of small voids whereas blow holes or gas pockets are comparatively bigger isolated holes are cavities.
  • They occur mainly due to entrapped gases.
  • The parent metal melted under the arc tends to absorb gases like H2, CO, N2 and O2 from the atmosphere.
  • These gases may also be produced due to coating gradients in the electrode (or) moisture, oil, grease etc., on the base metal. The causes may be summarised as
    • Improper coating of an electrode.
    • Longer arc.
    • High welding currents.
    • Incorrect welding techniques.
    • Electrodes with a damp coating.
    • Rust, oil, grease etc on the job.
  • High Sulphur and carbon contents in the base metal.

1.7 Surface Cracks:

Cracks (both external and internal):
  • Cracks may be on the microscopic or macroscopic scale.
  • They may appear in the base metal, base metal – weld metal boundary or in the weld metal. The crack may be on the weld surface or inside causes are
  • The rigidity of the joint (the members are not free to expand or contract).
  • Poor ductility of the base metal.
  • High sulphur and carbon content of these metal.
  • Electrode with the H2 content.
  • The presence of residual stresses.
  • Joining of high thermal expansion materials without preheating.
  • Joining of high thermal expansion materials without preheating.
  • Welding of ferrous materials by using hydrogen as a shielding gas.

2. Internal defects in welding:

Internal defects include slag inclusion, lack of fusion, necklace cracking and incomplete filled groove.

2.1 Slag Inclusion:

  • Slag is formed by reaction with the fluxes and is generally lighter.
  • It has low density. So it will float on the top of the weld pool. And would chipped off after solidification.
  • However, the stirring action of the high-intensity arc would force the slag to go into weld pool and if there is not enough time for it to float, it may get solidification inside the fusion and end up as slag inclusion.
  • Use of forehead welding technique in welding.
  • Incorrect select of flux powder.
  • Improper cleaning of the weld beads in multipass welding.
  • Undercut on the previous pass.
  • Incorrect manipulation of the electrode. Slag inclusion like property weakens the metal by providing the discontinuities.

2.2 Lack of fusion:

  1. Incorrect torch angle in gas welding
  2. Insufficient current conditions in Arc welding.
  3. Joining of high melting point and high thermal conductivity

2.3 Necklace cracking:

In the case of electron beam weld does not penetrate fully, a blind weld results. In such situations, the molten metal is unable to flow into the penetration cavity and wet the side walls of the workpieces. This will result in cracking, known as “Necklace Cracking” and has been noticed in all materials such as Ti alloys, stainless steels, nickel base alloys and carbon steels.

2.4 Incompletely filled groove:

Occurs in butt welds.
Causes for incompletely filled groove are:
  • Inadequate deposition of weld metal.
  • Use of incorrect size of the electrode.


1. Toyota Motor Corporation started in 1937 as a division of Toyoda Automatic Loom Works. While the Toyota Group is now best known for its cars, they are still in the textile business as well.
2. The founder of Toyota Motor Corporation actually spells his name T-O-Y-O-D-A. Kiichiro Toyoda, to be exact. The spelling of the company name was changed to Toyota because when it is written in Katakana (a Japanese script) it only takes 8 strokes to write, and 8 is a lucky number in East Asian culture.

3. Kiichiro Toyoda, son of the founder of Toyoda Automatic Loom Works, got ideas for the first Toyota cars from the United States. He traveled to the US in 1929 to investigate automobile production because Japan needed to start producing domestic vehicles due to their war with China. Early Toyota’s bear a striking resemblance to the Dodge Power Wagon and Chevrolet.
4. Even though Toyota started in Japan, the company has created more than 365,000 jobs in the United States.
5. The Korean War saved Toyota. The company was on the verge of bankruptcy, and produced only 300 trucks in June of 1950. In the first few months of the Korean War, the US ordered more than 5,000 vehicles from Toyota, and the company was revived.
6. Toyota first came to America in 1957.
7. In the year 2011, Toyota was ranked as the third largest car manufacturer in the world, behind General Motors and Volkswagen Group.
8. Toyota is the world’s leading manufacturer of hybrid vehicles, and there are more than 1,700,000 Toyota hybrids on the road right now.

9. Toyota invests $1 million dollars every hour in research and development worldwide. They do this in pursuit of building better and safe cars.
10. Eighty percent of Toyotas sold 20 years ago are still on the road today!