Engine Drive Train

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(E) Exhaust camshaft (I) Intake camshaft (S) Spark plug (V) Valves (P) Piston (R) Connecting rod


Typically forged or cast from iron, the crankshaft is a long cylindrical part of the engine which translates linear piston motion into rotational motion. The far end of the crankshaft is connected to the flywheel which is in place to reduce vibration. Connecting rods attach the mid-portion of the crankshaft to the pistons of the engine. These connecting rods are fastened onto the pistons and crankshaft by crank pins.

Cams and Camshaft

Cams typically come in three different types: the single overhead cam (SOHC), the double overhead cam (DOHC) and the pushrod.

In a single overhead cam, the camshaft spins and translating a force to the rocker arms which in turn open the valves. After the valves are opened a spring creates an opposing force which closes them as the cam turns. In the SOHC design, the camshaft is powered by the crankshaft.

The double overhead cam works much like the single, but instead of one cam per head there are two. This design is typically found in inline engines. As in the SOHC design the camshaft is powered by the crankshaft as well.

The pushrod cam is much like the SOHC and the DOHC, except for the location of the camshaft itself. In a pushrod engine the camshaft is inside of the engine block.


The core components of the piston system.

Fitted into a cylindrical chamber and sealed with rubber rings, a piston is a cylindrical shaped shaft that is used to create compression of the gas and air mixture in the engine. An explosion creates a linear motion of the piston which pushes on the connecting rod which translates the liner motion to rotational motion on the crankshaft. Pistons are often made from either low carbon steels or aluminum alloys.

How it works


The primary purpose of the crankshaft is to translate liner motion to rotational motion. The forces of these motions originate from an initial explosion of a gas-air mixture that occurs in a chamber that is sealed by the pistons. The linear motion of these pistons is transferred to the connecting rods. The connecting rods have an offset connection to crankshaft by crank pin bearings which allows for the connecting rods to oscillate on the crankshaft as the crankshaft rotates. This is the connection where the linear motion is translated to rotational motion. The rotational motion from the crankshaft is then connected to the camshaft as well as additional axes where the rotational motion can be transformed to work (i.e. the tires of a car).

Cams and camshaft

The cam, which controls the opening and closing of the valves, plays an important role in the drive train of the engine. Crucial timing is involved in this process, such that its malfunction would cause immediate failure. During the four-stroke cycle the air and gas valves alternate their opened and closed positions depending on the phase of the cycle. The opening and closing of these valves is determined by the position of the camshaft which is controlled by the crankshaft. The rotational motion of the crankshaft is transferred to specially set gears which simultaneously turn the cam which opens and closes the valves at particular times.



The piston has two primary functions:

1. To compress the air and gas mixture contained in the cylinder which creates a more forceful explosion

2. Translate the force created from the explosion to the rest of the engine

The sealed piston moves downward in the cylinder as it fills with the air-gas mixture. The momentum from the previous explosion causes the piston to move upwards compressing the mixture in the cylinder. The sparkplug ignites creating an explosion which pushes the piston in the downward direction. This action is the initial force which drives the rest of the engine.



The crankshaft concept has been around since it was invented in the 12th century by Al-Jazari.

Since then, the crankshaft has been adapted to suit the needs of a number of different engines, the largest markets being steam, aircraft, and automobile engines. More pistons have been added to suit larger engines, as well as the manufacturing of materials.

Changes made to the crankshaft have been in the construction materials and the process in which they are manufactured. One technology that was crucial to the evolution was the steel-making industry, in which new methods were developed to reduce impurities in the material. It wasn't until 1988 that the ladle furnance process was adopted to efficiently remove sulfur and gases, allowing the crankshaft to run smoother. Another important characteristic that the crankshaft needs to have is fatigue strength in the fillets, which has been improved by applying external forces by way of cold-rolling the material. This causes work hardening and residual stresses which both enhance the fatigue strength. Over the last 30 years the fatigue strength has improved by a factor of about 1.5.


Cams and camshaft

The cams and camshaft were first developed in order to perfect variable valve timing. When the engine was first built, every model varied so much and the cams and camshaft were a way to correct that error and variability. Just like the crankshaft, the camshaft has been modified slightly in order to accomodate different power and styles of engines. Also, in response to the cams, tappets were developed to make valve movement even easier.

The first twin-cam engine was brought about in 1954 and was called the Giulietta. Numerous other twin-cam engines premiered after that, all successful engine designs.


High tech piston with almost no side skirt to reduce material weight

The basic concept pistons got their start with steam engines. On a very large scale, steam power would drive a turbine to compress a giant piston mounted on a wooden beam. The cylinder in this case would be filled with water and the force of the piston acted as a water pump. But pistons as used in the internal combustion engines of today to drive the crankshaft have been in use for 141 years since their creation and implementation by Nicholaus August Otto.

Pistons from the start have generally always been cylindrical, hence the piston chamber being named the cylinder. Recently however other piston shapes have been employed, namely oval pistons used in Honda motorcycles. As engines have changed becoming more powerful, faster, or more efficient, the piston has also seen changes. Materials are improved to resist the increased heat for running at high rpm. Cast iron was used in the first engine but now an iron alloy mixed with silicon is used to improve heat strength. Lighter alloys are also used with thinner walls to improve efficiency. High performance drivetrains have machine drilled holes through the piston head to drastically reduce weight and improve efficiency even further. Even lubrication of the piston and crank assemblies have become more sophisticated to prolong the average lifespan of a piston.

Overall, the piston design has changed little since the early days of use but the materials have become more dependable with increasingly demanding operating conditions.



"Crankshaft." Wikipedia, The Free Encyclopedia. 6 May 2007 [1].

"Technical Developments and Recent Trends in Crankshaft Materials." 7 May 2007 [2].

Smith, Jeff. "Basics of a Crankshaft." 7 May 2007 [3].

Cams and camshaft

"Camshaft ." How Stuff Works. 6 May 2007 [4].

"Alfa Romeo Twin Cam engine." Wikipedia, the free encyclopedia. 7 May 2007 [5].

"Variable Valve Timing." Wikipedia, the free encylcopedia. 7 May 2007 [6].


"Piston." Wikipedia, The Free Encyclopedia. 6 May 2007 [7].

Honda. 8 May 2007 [8].

"Evolution of Piston Design.:" [9].

What's in an engine and why? Washington University. 6 May 2007 [10].

Piston. 6 May 2007 [11].

3D Parts (Piston and Cylinder Head)

Subassembly Bill of Materials
Part Name # Req'd Function Mfg Process Material CAD File Image
Connecting Rod 1 Transmits force of combustion to crankshaft torque Machined Aluminum Connecting Rod
Piston con rod.jpg
Connecting Rod Bracket 1 Bottom bracket for attaching to crankshaft Machined Aluminum Connecting Rod Bracket
Piston conrod cap.jpg
Connecting Screw 2 Screws connecting rod to bottom bracket Machined Screw Steel Connecting Screw
Piston con rod screw.jpg
Piston Dipper 1 Lubricates parts with oil from oil Pan Machined Steel Piston Dipper
Piston dip.jpg
Piston O-Ring 1 Fixes pin to piston head Wire Steel O Ring
Piston ring.jpg
Pin 1 Attaches piston head to armature connecting rod Machined Aluminum Pin
Piston pin 1.jpg
Piston Head 1 Compresses fuel in cylinder, transmits force of combustion to crankshaft, drives out exhaust Machined, treated Cast Iron Piston Head
Piston head 2.jpg
Compression Ring 2 Seals chamber for compression Machined, rolled Steel Compression Ring
Piston comp ring.jpg
Oil Control Ring 1 Controls the supply of oil Machined, rolled Steel Oil Control Ring
Piston oil ring.jpg
Head Gasket 1 Seals cylinder to ensure maximum compression and prevent leakage Molded, Heat Pressed, Coated MLS (multiple layers steel) Head Gasket
Head gasket.jpg
Cylinder Head 1 Head of valves and situates spark plug over the cylinder Machined, Molded, Welded Cast Iron Cylinder Head
Cylinder head.jpg
Head Bolt 8 Secures cylinder head to engine block Machined Steel Head Bolt
Head bolt.jpg
Piston Assembly 1 Transmits combustion force to drive the crankshaft Various processes Various materials Piston Assembly
Piston assem.jpg

3D parts (Drivetrain)

Subassembly Bill of Materials
Part Name # Req'd Function Mfg Process Material CAD File Image
Exhaust Valve 1 Allows gases to exit compression chamber after ignition Machined Steel Exhaust Valve
Exhaust valve.jpg
Intake Valve 1 Allows entry of fuel and air mixture before ignition Machined Steel Intake Valve
Intake valve.jpg
Valve Lifter 2 Connected to camshaft and open the valves at the correct time Machined Steel Valve Lifter
Valve lifter.jpg
Valve Spring 2 Loads the valves to maintain a force to open and close them Machined Steel Valve Spring
Valve spring.jpg
ValveSpring Clip 2 Holds the valve springs in place Machined Steel Valve Spring Clip
Valve spring clip.jpg
Crankshaft 1 Converts power from piston to shaft torque Cast then lathed Cast Iron Crankshaft
Crankshaft 1.jpg
Camshaft 1 Connected to the crankshaft with a gear. Makes one revolutions for every two crankshaft revolutions. Machined Steel, Plastic Camshaft
Cam Lobe 2 Pushes valve lifter up, opening the valve. Machined Steel Cam Lobe
Cam lobe.jpg
Camshaft Assembly 1 Essential to engine timing. Machined Steel, Plastic Camshaft Assembly
Camshaft assem.jpg
Valve Cover 1 Allows access to valve springs, etc. Machined Aluminum Valve Cover
Valve spring cover.jpg
Valve Cover Screw 2 Fasten valve cover to block. Machined Steel Valve Cover Screw
Valve cover screw.jpg
Valve Cover Rubber Connect 1 Mates valve cover to tube. Molded Rubber Valve Cover Rubber Connect
Valve rubber connect.jpg
Valve to Carburetor Tube 1 Connects carburetor to valves. Extrusion Aluminum Valve to Carburetor Tube
Valve carb connect.jpg
Carburetor Rubber Connect 1 Mates carburetor to tube. Molded Rubber Carburetor Rubber Connect
Carb rubber connect.jpg
Valve Cover Assembly 1 Covers valves and connects to carb. Various Steel, Aluminum, Rubber Valve Cover Assembly
Valve cover assem.jpg

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