Valve train noise is usually due to excessive clearance between two internal engine parts.
Each valve utilizes a valve spring that returns it to its original closed position.
So, If a valve spring has broken or a camshaft lobe is worn down; it will cause the engine to create a tapping or clicking sound; due to the excess clearance.
Valve train noise is similar to a clicking sound of a sewing machine. The sound frequency of the valve train noise is one-half the crankshaft speed.
A clicking lifter is one very common valve train noise. If the engine is equipped with solid (mechanical) lifters; fixing this usually requires an adjustment.
Most likely because the amount of lash or free play is far too excessive. The problem with diagnosing and correcting valve train noise is that there are many components that can cause undesirable sounds.
Not every noisy valve train is suffering from improper adjustment. For this reason, even after the valves are adjusted properly, the engine may still be noisy. If this is the case, then the problem is not with the lash; instead, a mechanical failure due to wear is probably causing the sound.
Though there are many possible causes, the valve lifter is often the source of the noise. In any hydraulic application; another cause of valve train noise can be the result of machining of the cylinder head and valve seats; which changes the rocker-arm geometry.
Many mechanics think that this is caused by faulty hydraulic lifters; that is incorrect. The lifter is only responding to the conditions and trying to adjust for them. That’s why it is critical to make sure that the valve train is the culprit; when chasing any excessive noise before it becomes a major issue.
It is important to remember that several different conditions can produce a noise; identical to that caused by a failed or failing valve lifter.
Some of these are;
- Lack of lubrication between the rocker arm and the pushrod
- Lack of lubrication between the rocker arm and the end of the valve stem
- Excessive valve guide-to-valve stem clearance
- Badly worn valve tips and/or rocker arm pads
- Worn camshaft lobes
- A loose valve seat on heads with inserts
- A warped valve
- Excessive clearance between the lifter and the lifter bore hole in the block
- A loose rocker-arm shaft
- A broken valve spring
If the engine noise is not caused by one of the listed issues it may be a hydraulic valve lifter. Now you will need to isolate the failed lifter. A simple method is to use a piece of garden hose. Remove the valve covers. With the engine running, place one end of the hose near the spring retainer of each intake and exhaust valve; put the other end of the hose to your ear. Finally, It will be very apparent which is the offending valve lifter.
Other ways to find a faulty valve lifter. With the engine shut off. Push down on each of the rocker arms on the pushrod side. If the rocker arm is free to move or there is a spongy feeling; it is a good indicator that the valve lifter is leaking down too fast; or not retaining oil from the engine.
Once you locate the lifter that is causing the noise, you will need to determine the reason for its malfunction.
There are four types of noise you may experience. An inoperative or failing valve lifter may cause any one of them;
Loud, Rapping Sound
A stuck plunger inside the body of the lifter could also be the cause. This is usually due to excessive varnish between the plunger and body.
Also by dirt or other foreign materials wedged between the plunger and body. Another cause of a loud rapping sound is an excessively worn base or foot on the lifter itself.
Moderate Clicking Noise
This can be the result of excessive varnish. Wear on the bottom of the lifter mat also be a source of noise. The noise level depends on the amount of varnish and the degree of wear. Two other causes of a moderate clicking noise are excessively fast or slow leak down.
Slow leak down generally will cause the engine to be noisy only when cold and the oil is thick. With fast leak down, the valve train will be noisy when the engine is warm. Fast leak down will also occur if the ball-check in the lifter fails to seal.
This type of noise is hard to locate by its very nature. There will be a few clicks; and then it will be quiet; but the noise will reappear after a short period of time.
The usual cause of intermittent clicking; is a very minute piece of dirt that holds the ball check off the seat for a few seconds; and then passes through. In rare cases, the cause of the sound is a pitted or flat spotted ball-check.
General Valve Train Noise
When the sound is throughout the entire valve train; the cause is usually the weight of the oil or the oil supply itself. Too much oil in the crankcase will cause foaming and aeration. When air gets into the lifters, they will fail to operate properly. Insufficient oil supply to the lifters can also cause general valve train noise.
This could be the result of too little oil in the crankcase; an oil pump not operating properly; or clogged main oil gallery lines. Excessively thick engine oil will cause entire valve train noise when cold-starting an engine. The noise will diminish when the oil warms up and starts to flow properly. An engine with thick oil will be more prone to noise in colder weather than during the summer months.
So, As a mechanic you hear the phrase “my engine is making a strange noise” relatively often. Though there are many possible causes, the valve lifter is often the source of the noise.
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