Editing Lifters

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[[File:Hydraulic Lifter.jpg|thumb|200px|left|Generic hydraulic lifter]][[File:Schubeck hydraulic lifter made for zero lashing.jpg|thumb|150px|right|[http://www.schubeckracing.com/flathydraulic.html '''Schubeck hydraulic lifter'''] made to be zero-lashed]] <br><br>

==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.

==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"). Originally virtually all lifters were a solid 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"). 

The hydraulic lifter (or "tappet") 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.

===Flat tappet===
Flat tappet lifters are flat on the bottom. Actually they're not perfectly flat, they have a very gradual radius ground onto them to help the lifter to rotate (along with the angle of the cam lobe), and resemble a cylinder of steel with a snap ring on one end holding in a pushrod cup.

Flat tappet cam/lifter valve trains were the primary form of valve actuation for domestic engines from the early '50s until about the mid-'80s. They were reasonable durable and reasonably reliable, although there were better designs. Not until the EPA mandated a change in the motor oil formulations did they fall out of favor. 

====Mushroom flat tappet lifter====
Mushroom lifters were used in high performance flat tappet applications. The larger diameter of the mushroom lifter's foot allowed it to handle more aggressive cam lobe profiles. They weren't used on production engines much at all, the assembly process when using them is labor intensive- something the OEM always tries to avoid.

===Hydraulic lifter===
The hydraulic lifter was a mainstay for over 40 years in domestic automobile engines. Its design allowed a basically maintenance free valve train. They were quiet and reliable.
[[File:Lifter cutaway preload.jpg|border|400px|right]]

====Fast bleed down 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 putting a groove on the plunger by EDM (electron discharge machining) or laser. This groove allows the oil to bleed out of the chamber at a faster, yet controlled rate. This allows the lifter to vary 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.
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Below, the groove on the plunger can be seen at the arrows. The plunger is partially removed from the lifter body; the retainer clip and pushrod cup were previously removed.

[[File:Rhodes lifter groove.jpg]]

===Solid lifter===
Before the hydraulic lifter, the solid or "mechanical" lifter was used exclusively. 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.

Solid flat tappet lifters are still used in some high performance engines, solid roller valve trains are the choice for racing when allowed and street/strip engines used at high RPM. They are as durable as a hydraulic lifter in flat tappet form, but suffer the same wear problems due to the decrease of wear additives that have been removed from current motor oil.

Solid lifters are not used in modern engines because they make enough noise that they could confuse knock sensors.

===Roller lifter===
Shown below is a GM hydraulic roller lifter. The arrow shows the location of the cup, spring and check ball assembly mentioned [[Lifters#Replacing lifters|'''below''']].
[[File:Oem hyd roller lifter expolded view.jpg|left|frame|OEM GM hydraulic roller lifter]]
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==How to tell a hydraulic lifter from a solid lifter==
The rule of thumb for visually discerning a solid lifter from a hydraulic lifter is the fact that hydraulic lifters contain a spring loaded plunger assembly that is retained with a snap ring or wire lock. A hydraulic lifter will compress, but this can be difficult to see once the hydraulic lifter is filled with oil unless the lifter is placed into compression long enough for the oil to bleed out of it, allowing the lifter to compress.

Some solid lifters are one piece construction. Others look much the same as a hydraulic lifter, but good quality solid lifters will usually have an internal C-clip type retainer rather than a wire clip. The clip is visible when looking at the lifter from the top where it contacts the pushrod. 

On a solid lifter valve train, usually if the lifters all have about the same lash while on the base circle of the cam, '''and''' the lifters do not compress either by placing a thumb over the pushrod seat of the rocker and pressing down or by cranking in some preload and waiting to see if the spring pressure bleeds the lifter down, they're solid. To clarify, the intake and exhaust lash measurement may well be different from ''each other'', but similar among themselves, i.e. intake valve lash all about the same and the exhaust valve lash also all about the same. Like seeing 0.016" intake clearance and 0.020" exhaust clearance as an example. 

Solid lifters will have a distinctive "ticking" sound at idle caused by the clearance between the tip of the rocker arms and the valves.

If you adjust the rocker arm and lifter to "zero lash" using a valve whose lifter is on the heel of the camshaft lobe, if you then adjust the rocker arm nut down further than zero lash, a hydraulic lifter will compress and allow this to happen. If it's a solid lifter, you will be compressing the valve spring and you will feel considerable resistance to turning the adjustment nut down further. A hydraulic (in most cases) should allow at least a full turn of the adjustment nut, if not two or more turns before the valve spring starts to compress. If the engine has just been running, there will be resistance caused by the hydraulic lifter being pumped full of oil, but after waiting after turning down the adjustment nut, a hydraulic lifter will "bleed out", allowing the lifter to compress. A solid lifter won't do this, and the valve spring will remain compressed.

If you find that you have solid lifters but don't know what lash to adjust them to, you can use 0.020" to 0.025" clearance on both intake and exhaust as a starting point.

==Break in of flat tappets==
The motor oil formulation has been changed due to concerns for the environment. These changes involve a reduction of the wear additive essential for a flat tappet cam to survive the harsh conditions they operate under. Because of this, special steps must be taken at break in and at oil changes to prevent premature wear or failure of the flat tappet cam and lifters.

For more on the steps that need to be taken to avoid a cam and lifter failure, see [http://www.crankshaftcoalition.com/wiki/Camshaft_install_tips_and_tricks Camshaft install tips and tricks].

==Replacing lifters==
[[File:Lifter expolded view.jpg|thumb|200px|left|Arrow points to check ball retainer]]
[[File:Lifter clips 002.jpg|thumb|350px|Three styles of lifter cup retainers. The [http://www.truarc.com/pdfs/Truarc%20Catalog.pdf internal C-clip type] is stronger and should be used especially with solid lifters or when "zero lashing" lifters.]] 
{{Caution}}Lifters and cam lobes become wedded as soon as the engine fires up and the cam is broken in. From that point forward, the same lifter '''has''' to be kept on the same lobe, preferably in the same engine. To replace a faulty lifter with a new lifter (or to replace a used cam with a new cam, reusing the same lifters) is to ask for a catastrophic failure requiring the engine to be torn down to remove the shrapnel left from the destruction of the cam lobe(s) and lifter(s).<br><br>

Before replacing a stuck or noisy lifter with a new lifter (which should be considered only in an emergency situation), disassemble the lifter that is in question. You will see a cup, spring and check ball retainer (left) snapped onto the bottom center of the "piston" of the lifter. Often all that has happened is the cup assembly isn't fully seated into the recess on the bottom of the piston, or a speck of dirt has lodged between the check ball and seat. <br style="clear:both"/>

Remove the cup using a pick and see that the tiny spring and check ball are there and that the ball isn't scored and that the seat on the piston that the ball seals, doesn't have any ridge or imperfections that would prevent the ball from seating properly. 

A better choice if the lifter's bore is OK but the piston is found to be unrepairable, would be to replace the piston assembly from another identical lifter and reuse the lifter body, then replace the lifter back on the same lobe it came from.

{{Note1}}The lifter is the most precisely machined part in the engine. The piston OD is matched to the lifter body ID, the close tolerances are required to give the correct amount of bleed down. For that reason, swapping out the piston from one lifter to another will not always work, so plan on having to go through more than one lifter to find a good match to the old piston OD. The MAIN thing is that the piston not be too tight. Slightly loose will still perform OK, although there's a chance there could be some slight tapping at idle. But if the lifter and cam cannot for whatever reason be replaced as a set, this is STILL preferrable to putting a new lifter on a used cam.   
*[[Lifters#Roller lifter|'''Return to Roller lifter''']].

[[Category:Engine]]
[[Category:Adjust valves]]