Hydraulic lifters, also known as hydraulic tappets, help to ensure your vehicle runs quietly and performs as it should. They are situated by each of the engine’s valves. Testing your hydraulic lifters, if you suspect low pressure or another fault, could prevent a problem from escalating. Also, repairing hydraulic lifters when they stop working efficiently is vital as it can end up causing further, potentially costly damage to the surrounding parts.
How Do Hydraulic Lifters Work?
The purpose of a hydraulic lifter is to create clearance inside the valve train. It does this by using a plunger and a spring which work in union and are driven by the oil in the lifter itself. It is connected to the hydraulic valve with a rocker arm (a small rod).
Common Problems Associated With Hydraulic Lifters
A clear sign that you have a problem with your hydraulic lifter is a rhythmical tapping noise.
This could be due to a sticky lifter caused by dirt or other deposits in the oil/engine but it could also be a sign of something else.
The tapping will eventually get faster and faster and will turn into a knocking and then a banging if left unchecked. We highly recommend you don’t leave it that late as it is the parts banging together that are making the sound. This can cause excess wear and even break them completely which all adds up to the eventual fix cost.
Other things that can go wrong with a faulty hydraulic lifter include cylinder misfiring, which presents as a loss of acceleration. If left unchecked, the faulty lifter can push the rod out of its position causing a dead cylinder. This can go on to cause a multitude of other problems and damage and the vehicle should not be driven in this state in case it causes irreparable or very costly damage.
Why Hydraulic Lifters Fail
The following problems may be the reason behind the fault with your hydraulic lifter:
- Incorrect engine oil for your engine type.
- Low oil.
- Dirty oil.
- Wear and tear caused by high mileage.
- Lack of regular servicing.
- Sticking check valve.
- Problem with the lifter spacing.
Repairing & Testing A Hydraulic Lifter
Testing A Hydraulic Lifter
To test a hydraulic lifter, a ram is attached to a vertical standard, which is in turn attached to a base. At one end of the arm of the ram, there is a weight which operates it. At the other is the tester cup which is filled with a test fluid, usually light oil. The lifter is placed in the cup and covered with light oil.
The steel ball is put into the pushrod cup and the plunger worked until the lifter is full of liquid with no air bubbles. Then, the arm is adjusted to ensure that the ball in the pushrod cup is just touching it.
Prepare your timer (a watch or phone will do). Lift the lever, start the timer and then let the weighted ram move the plunger down. This will move the pointer across the scale, once it has reached the end, stop the timer – the time it has taken will give you the leak down rate.
It is recommended that you repeat the test a few more times to get an accurate rate. The ideal time leak down rate is anywhere between 5 seconds and 1 minute for a used lifter with new ones taking between 10 seconds and 1 minute. A sticky lifter will be slower and a worn or leaking valve will go too fast.
Repairing A Hydraulic Lifter
The following tips will help maintain your hydraulic lifter and can potentially extend the life of one that has begun to tick or tap.
- Change the oil and ensure you are using the right kind of oil.
- Use an oil addictive to improve the oil quality and help clean residue from the lifters as it passes through them.
- Get a hydraulic engineer or mechanic to adjust the lifter spacing or try it yourself if you know what you are doing, your vehicle manual will have lifter spacing details.
To replace the lifters or other component parts, it is best to consult a professional. It is likely they will need replacing. Take the mechanic or engineer’s advice regarding replacements but generally speaking, although used lifters are available, it is not always cost-effective to use these due to labour costs. Similarly, if one lifter has worn out the others will likely follow so it is better to replace them all in one go.
Conclusion
If you hear a knocking or tapping, then it is best to have it checked by a professional. Although, if you have the right equipment and tools, you could try testing and attempt the quick fix solutions mentioned above yourself.
If you require any advice on hydraulic lifters, would like your lifters professionally tested or have any questions about any other aspect of hydraulic servicing and repairs, then get in touch with us as MCH Hydraulics and our team of experts will be happy to help.