digplanet beta 1: Athena
Share digplanet:


Applied sciences






















A hydraulic valve lifter, also known as a hydraulic tappet or a hydraulic lash adjuster, is a device for maintaining zero valve clearance in an internal combustion engine. Conventional solid valve lifters required regular adjusting to maintain a small clearance between the valve and its rocker or cam follower. This space allowed for thermal expansion, and prevented the parts from binding. This clearance space meant noisy operation and earlier wear, as the parts would rattle against one another until the parts heated up and expanded. The hydraulic lifter was designed to compensate for this tolerance, allowing the valve train to operate with zero clearance--leading to quieter operation, longer engine life, and eliminating the need for periodic adjustment of valve clearance.

The hydraulic lifter, situated between the camshaft and each engine's valve, is a hollow steel cylinder encasing an internal piston. This piston is held at the outer limit of its travel with a strong spring. The lobed camshaft rhythmically presses against the lifter, which transmits the motion to the engine valve one of two ways:

1) through a pushrod which actuates the valve via a rocker mechanism; or
2) in the case of overhead camshafts, via direct contact with the valve stem.

Oil under constant pressure is supplied to the lifter via an oil channel, through a small hole in the lifter body. When the engine valve is closed (lifter in a neutral position), the lifter is free to fill with oil. As the camshaft lobe enters the lift phase of its travel, it compresses the lifter piston, and a valve shuts the oil inlet. Oil is nearly incompressible, so this greater pressure renders the lifter effectively solid during the lift phase.

As the camshaft lobe travels through its apex, the load is reduced on the lifter piston, and the internal spring returns the piston to its neutral state so the lifter can refill with oil. This small range of travel in the lifter's piston is enough to allow the elimination of the constant lash adjustment.


The first firm to include hydraulic lifters in its design was the Cadillac V 16 engine (Model 452) first offered in 1930. Hydraulic lifters were popular on automobiles designed in the 1980s, but most newer cars have reverted to bucket-and-shim mechanical lifters. Although these do not run as quietly and are not maintenance-free, they are cheaper and rarely need adjustment because the wear caused by operation is spread over a large area.[citation needed]


There are a number of potential problems with hydraulic lifters. Frequently, the valvetrain will rattle loudly on startup due to oil draining from the lifters when the vehicle is parked. This is not considered significant provided the noise disappears within a couple of minutes, typically it usually only lasts a second or two. A rattle that does not go away can indicate a blocked oil feed or that one or more of the lifters has collapsed due to wear and is no longer opening its valve fully. The affected lifter should be replaced in the latter situation.

It is a myth that in certain circumstances, a lifter can "pump up" and create negative valve clearance. The engine oil pump cannot generate enough pressure to cause "pump-up". The problem is due to weak valve springs which permit float at high engine speeds. The followers attempt to take up what they see as extra clearance. As this speed is maintained, the lifter will continue to expand until the valve is held off its seat when it should be closed. Maintenance of the valve springs at the correct strength is therefore very important to avoid engine damage.


Tappets should be fitted while FULL of oil/diesel liquid: the original-equipment manufacturers specify that the installer should be unable to compress them BEFORE re-fitting, given that these components are intended to take up the slack in the valve train. The reason they tap when faulty is because they cannot keep the gap correctly.

Original courtesy of Wikipedia: http://en.wikipedia.org/wiki/Hydraulic_tappet — Please support Wikipedia.
This page uses Creative Commons Licensed content from Wikipedia. A portion of the proceeds from advertising on Digplanet goes to supporting Wikipedia.
9437 videos foundNext > 

Rebuilding Hydraulic Lifters

This video shows the disassembly, cleaning, and rebuilding of hydraulic valve lifters. These belong to a VW 16V head but many are similar. A couple of these ...

How-To: Inspect a Hydraulic Valve Lifter

Here I show you how to inspect a valve lifter, and explain what causes premature lifter wear. Thanks for watching. Please subscribe!

hydraulic tappets / hydraulic valves (or hydraulic lifters)

The internal work of the hydraulic valve lifters, commonly found on lots of cars and some motorcycles too. the idea behind this is that LIQUIDS CAN NOT BE CO...

Hydraulic Valve Lifter

Hydraulic Valve Lifter Get the book here: https://www.createspace.com/4321251 Video lays the groundwork for a discussion on hydraulic valve lifter, what they...

Hydraulic lifter bleed down. Bad Hydraulic Lifters

352ci Ford in my 1966 F-100 shortbed. Just finished installing a new cam and lifters. Even needed new pushrods to get the preload correct. After all that, wh...

How to fix hydraulic lash adjuster tick on miata, ford, Hyundai, Mercury, and KIA.

These exact same lifters are also are used on Ford Probe, Escort, Hyundai Accent, Optima, Sephia, Spectra, Mazda 626, millenia, Protege, MX-6. mx-5, mx-3, 62...

(29) Golf Gti Mk2 1.8 Hydraulic Tappets Guides

Placing the hydraulic tappets home. Just make sure everything is really well oiled.

How to adjust hydraulic lifters on a BBC/SBC - 3

This is an easy way to adjust your hydraulic lifters...either rollers or flat tappet. Even if you have never done anything like this before, you can get the ...

ASN Hydrostoessel // Hydraulic Tappet

Hydrostoessel // Hydraulic Tappet defekt.

Roller Cam vs Flat Tappet Cam - Summit Racing 101

Dave takes a quick dive into the basics of camshafts and their lifters, specifically the roller camshaft lifter and the flat tappet camshaft lifter. Dave dis...

9437 videos foundNext > 

1 news items

Autochannel (press release)

Autochannel (press release)
Sat, 30 Aug 2014 12:52:30 -0700

Think adjustable hydraulic tappet; there are still valve springs so if anything in the electrohydraulic system fails, the valve closes and does not catastrophically meet with the piston. The exhaust valves are actuated normally, by the single overhead ...

Oops, we seem to be having trouble contacting Twitter

Talk About Hydraulic tappet

You can talk about Hydraulic tappet with people all over the world in our discussions.

Support Wikipedia

A portion of the proceeds from advertising on Digplanet goes to supporting Wikipedia. Please add your support for Wikipedia!