Lifters
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==Overview== | ==Overview== | ||
| − | The lifter of an overhead valve engine rides on the cam lobe, actuating the push rod that directs the movement to the valve stem. It is an essential part of the valve train and the importance of a proper break in between the lifter foot of a flat tappet and the cam cannot be overstated. | + | The lifter (or "tappet") of an overhead valve engine rides on the cam lobe, actuating the push rod that directs the movement to the valve stem. It is an essential part of the valve train and the importance of a proper break in between the lifter foot of a flat tappet and the cam cannot be overstated. |
==Types of lifters== | ==Types of lifters== | ||
| − | Lifters are either hydraulic or solid. They can be either a "flat tappet" type, or a roller type. These two types can be either hydraulic or solid (also called "mechanical") | + | Lifters are either hydraulic or solid. They can be either a "flat tappet" type, or a roller type. These two types can be either hydraulic or solid (also called "mechanical"). |
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===Flat tappet=== | ===Flat tappet=== | ||
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===Hydraulic lifter=== | ===Hydraulic lifter=== | ||
| − | The hydraulic lifter | + | The hydraulic lifter has been a mainstay for over 40 years in domestic automobile engines. Its design allowed a basically maintenance free valve train. They are usually quiet and reliable. |
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| + | The hydraulic lifter was invented as a means of reducing maintenance and quieting the valve train. Generally the pressure from the engines oil pump would provide the "self adjusting" hydraulic action and keep the lifter tight to the camshaft and push-rod. This action was well controlled by design within the normal operating ranges of most passenger vehicles although over-extension, known as lifter "pump up" of the lifter can occur at elevated RPM, allowing the valves to be held off the seat causing a loss of power. This means mechanical lifters are the preferred type of lifter for high RPM applications. Later versions of performance hydraulic lifters included anti-pump up-types and roller lifter types as well. | ||
| + | *[http://www.youtube.com/watch?v=lorANZ1Tptw '''Click here'''] for a video that shows an animation of a hydraulic lifter. | ||
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[[File:Lifter cutaway preload.jpg|border|400px|right]] | [[File:Lifter cutaway preload.jpg|border|400px|right]] | ||
[[File:Pontiac service manual lifter diagram.jpg]] | [[File:Pontiac service manual lifter diagram.jpg]] | ||
| − | ====Fast bleed down lifter==== | + | |
| + | ====Fast bleed down hydraulic lifter==== | ||
An example of a fast bleed down hydraulic lifter is the [http://www.rhoadslifters.com/ Rhodes] lifter. The Rhodes lifter accomplishes the fast bleed down by machining a precision groove on the plunger, possibly by using EDM (electron discharge machining) or laser. This groove allows the oil to bleed out of the lifter at a faster- yet controlled- rate. This allows the lifter to lower the lift and duration of the cam at lower RPM, typically from idle to ~3000 RPM or so, depending on the valve spring pressure and oil viscosity. At higher RPM, the lifter behaves as a normal lifter would. | An example of a fast bleed down hydraulic lifter is the [http://www.rhoadslifters.com/ Rhodes] lifter. The Rhodes lifter accomplishes the fast bleed down by machining a precision groove on the plunger, possibly by using EDM (electron discharge machining) or laser. This groove allows the oil to bleed out of the lifter at a faster- yet controlled- rate. This allows the lifter to lower the lift and duration of the cam at lower RPM, typically from idle to ~3000 RPM or so, depending on the valve spring pressure and oil viscosity. At higher RPM, the lifter behaves as a normal lifter would. | ||
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===Solid lifter=== | ===Solid lifter=== | ||
| − | + | Originally, virtually all lifters were a solid or "mechanical" lifter design that required regular maintenance to check and set clearance in the valve train to account for wear during normal engine operation. This insured that the valve would fully seat against the valve seat, which is important not only for good engine performance but for the valve (especially the exhaust valve) to transfer heat from the valve into the seat then on to the cooling system to prevent the valve from rapidly eroding (aka a "burned valve"). | |
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| + | With a solid lifter valve train, a predetermined amount of play is introduced between the tip of the closed valve and the rocker arm. This clearance is sufficient to allow for heat expansion of the components during operation. | ||
The solid lifter valve train requires periodic maintenance to account for wear, else the valve could eventually be damaged by insufficient clearance. That causes the exhaust valve to overheat and/or burn and a loss of performance can result from the intake not seating and sealing as it should. Excessive clearance can cause valve train damage and reduced performance and mileage. | The solid lifter valve train requires periodic maintenance to account for wear, else the valve could eventually be damaged by insufficient clearance. That causes the exhaust valve to overheat and/or burn and a loss of performance can result from the intake not seating and sealing as it should. Excessive clearance can cause valve train damage and reduced performance and mileage. | ||
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