Valve Train
Valve Train
The valve train is considered to be all the components that are involved in introducing and releases gases into and out of the engine. Most if not all of the ways to introduce and release the gases involve valves (except two stroke engines.) But the setups for running the valves are different.
The main component of the valve train is the cam shaft. The cam shaft is just a long rod with lobes, or cams, on it. The cam shaft basically tells the valves when, how long, and how far to open by the size of the cams. The difference between many of the setups is the placement of the cam shaft.
Basics
The camshafts are connected to gears, or sockets. These gears have a belt around them that is ran from the crankshaft. This belt is called the timing belt. This belt rotates the camshaft so that it will open the valves at the right time. The lobes on the camshaft push rockers. These rockers are little pivoting metal peices that connected to a thin rod in the center. When the camshaft pushes one end of the rocker up, the other end goes down. When the rocker goes down it pushes the valve down, hence opening the valve. The valve has a spring wrapped around it on the outside of the cylinder that pushes the valve closed when the camshaft is not pushing it.
Different Setups
If you read the SOHC Engine Vs. DOHC Engine page then those are the first two types. The third type of engine/valve train is refered to aa a pushrod engine. It is usually just in V-Type engines. There is only one cam shaft located on the block, instead of in the header, in the center of the V. It is connected to the rockers on both sides by what is called a pushrod. When a cam on a cam shaft comes up it pushes the pushrod up and causes the valves to open that way.
Variable Valve Timing
As discussed on the VTEC
page, has 3 cams for 2 valves. The cams switch at a certain rpm to get better performance. Another type of Variable Valve Timing takes place in Ferrari's. The cams are longer and they slope from left to right adding another dimension to the system. When the engine is moving faster the whole cam shaft is pushed slowly by a separate mechanism. As it slides, the cam gets larger and more agressive so that it makes the engine more efficient and powerful.
Problems
Valves can experience many problems and cause many problems for the engine it it attached to. If you replace a camshaft or any other part of the valve train it is crutial that you keep it all lined up. Otherwise your valves will open at the wrong time and create a lot of damage. Many car tuners will experiment for hours on a wheel dyno fixing their valve timing so that they get the best performance from it.
If you change the camshaft, you must be sure of the valve clearance. If a valve moves to far down in its cycle it will hit the piston and will be ruined. This can be prevented by buying a specific camshaft for the car you buy.
The springs on the valves must be very strong. They are compressed at very fast speeds when the engine goes into the high rpms. If they are not strong enough they can brake and/or not push backenough or in some cases at all. This would cause the valves to float. In the worst case they would hit the pistons and do damage to the cylinders.
Return to Main Page
Copyright © 2002 ppddaiddddyy's site
All Rights Reserved.
