Diagnosing Valve Train Noise and Other Symptoms of a Bad Valve Train

Updated on October 19, 2018
Dan Ferrell profile image

Dan Ferrell writes about do-it-yourself car maintenance and repair. He has certifications in automation and control technology.

The valve train can develop problems that affect engine performance.
The valve train can develop problems that affect engine performance. | Source

Valve train problems can cause all kinds of engine performance problems, including:

  • High oil consumption
  • Blue smoke
  • Cylinder head noises
  • Misfires

Valve train problems may show up when, for example:

  • you allow the oil level to drop;
  • forget to change the oil at regular intervals;
  • operate the engine when it's overheated;
  • or go long periods without maintenance or without fixing engine problems.

But valve train problems can happen even if you service your engine on time and make necessary repairs, especially if your engine has a lot of mileage on it.

Whatever the reason, this guide helps you diagnose the most common valve train problems and their potential sources. Diagnose the problem sooner than later to avoid expensive repairs.

If you are concerned about an engine noise and aren't sure where it is coming from, check this article on diagnosing engine noise before you start troubleshooting valve train components. It will help you identify the origin of the noise, anywhere in the engine.

To make it easier, the following sections are divided into symptoms that can be produced by different types of valve train problems. Take a look at the index below. If one or more of these symptoms seems similar to the one you are dealing with, head over to that section. Reading additional sections will give you more ideas about types of problems that may develop and help you in your repair project.

Before you begin, though, keep in mind that although we are focusing here on valve train issues, none of these symptoms are exclusive to the cylinder head. So try to get as many clues as possible during your diagnostic phase, and troubleshoot suspected components when necessary. You'll find some troubleshooting suggestions to do this in the appropriate sections as well.

So let's start.

Index
I. Blue Smoke is Coming Out the Tailpipe
II. My Engine Misses at Idle
III. My Engine Backfires
IV. I Can Hear a Clatter
V. I Can Hear a Rattling Noise
VI. I Hear a Tapping Sound
VII. My Engine Has No Power
VIII. Preventing Valve Train Issues
Valve problems can result in tailpipe smoke.
Valve problems can result in tailpipe smoke. | Source

I. Blue Smoke Is Coming Out the Tailpipe

A worn valve stem seal, like a worn valve stem or guide, can let oil leak down the valve guide and into the combustion chamber. If enough oil leaks through, this can cause:

  • spark plug fouling
  • cylinder misfire
  • blue smoke through the tailpipe

Usually you'll notice the blue smoke during engine startup and deceleration.

How to Replace a Worn Valve Stem Seal

Often, you can replace worn valve stem seals without removing the cylinder head.

Some shops fill the combustion chamber with compressed air to hold the valve in place while replacing the seals. At home, you might not have compressed air, but you can use caulking cord or similar soft, thick cord instead.

  1. Set the transmission to Park (automatic) or Neutral (manual), and set the emergency brakes.

  2. Remove the spark plug from the cylinder you need to work on.

  3. Turn the piston you'll be working on to BDC (bottom dead center). Rotate the crankshaft using a socket and breaker bar on the crankshaft front bolt. If necessary, remove all the spark plugs to make it easier to rotate the crankshaft.

  4. Fill the cylinder with about 5 ft of cord. Use a large screwdriver to push the cord through the spark plug hole. The end of the cord should hang out of the spark plug hole after filling the cylinder so that you can pull it out afterwards.

  5. Bring the piston up to TDC (top dead center) by manually turning the crankshaft. This allows the cord to press against the valve and hold it in place.

  6. Now you can use a valve spring compressor to replace the valve seal.

  7. Install the new valve seal.

  8. Reinstall the rest of the valve components.

  9. Turn the piston towards BDC and remove the rope.

Consult your vehicle repair manual, if necessary.

A fouled spark plug due to oil leaks can cause a misfire.
A fouled spark plug due to oil leaks can cause a misfire. | Source

II. My Engine Misses at Idle

Extreme high temperatures in the combustion chambers can damage the valve face or seat. High temperatures like this can be caused by an EGR valve that is stuck closed or by carbon deposits. If heat chips the surface of the valve face or seat, this can cause:

  • Combustion pressure leak
  • Misfire, usually at idle
  • Noisy valve train

How to Diagnose a Burned Valve

  • If compression pressure is leaking through an intake valve, you may hear a puffing sound coming out of the carburetor or throttle body.
  • If the pressure is leaking through an exhaust valve, you may hear a puffing sound coming through the exhaust tailpipe. Watch the following video for an example of a bad exhaust valve noise coming through the tailpipe.

To confirm a compression leak and its probable source, do a compression test, cylinder leakage test, or vacuum test.

With a burned valve, you'll need to remove the cylinder head, machine the valve seats, and replace the burned valves (or all the valves).

III. My Engine Backfires

Cylinder head problems may come from a floating valve as well. A valve-float condition occurs when the valve is unable to close and seal the combustion chamber properly. Usually, this happens because of a weakened or broken valve spring.

A weakened spring is more common on high-mileage engines. After miles of service the spring loses strength, allowing the valve to float.

A valve can also float because of a broken valve spring. Usually, the clearance between the valve stem and rocker arm widens and causes a clatter noise too.

Any of these conditions can result in:

  • Engine miss
  • Tapping noise
  • Backfire

Although mechanical problems are the main cause of a floating valve, excess engine speed can also prevent a valve from closing properly, leading to engine performance problems.

How to Diagnose a Clattering Sound Coming From the Cylinder Head:

  1. Remove the valve cover
  2. Idle the engine
  3. Watch the valve movement
  4. Push the suspected valve rocker arm with your thumb to quiet the valve
  5. If the noise stops or changes significantly, you've found the problem valve.

If you suspect a worn valve spring, and the other valve train components seem to be in relatively good shape, remove the spring for inspection. See the method described in Section 1 above to remove a valve seal.

There are three main measurements used to check a valve spring. If the spring is not broken:

  • Use a sliding caliper to check for valve spring installed height.
  • Use a combination square to check for valve spring free height.
  • Use a valve spring tester to check for valve spring tension (you may need to take the spring to a machine shop for this test).

Compare your results to the specifications. Consult your vehicle repair manual.

Low oil level can cause valve train noise.
Low oil level can cause valve train noise. | Source

IV. I Can Hear a Clatter

Hydraulic lifter problems are similar to those of a worn valve guide or rocker arm (see the following sections). A sticking, worn or failed lifter can cause a clatter sound as well.

However, identifying a problem with one or more lifters can be tricky. Make these preliminary checks:

  1. Check for correct oil level.
  2. Examine oil condition.
  3. Test valve adjustment.
  4. Check the condition of other valve train components (rocker arms, pushrods, springs).

If none of these components seems bad, you may be dealing with a sticking lifter.

Before you begin to disassemble valve train components, you may want to try a detergent additive for the engine oil, if your vehicle uses hydraulic lifters. The additive may help to restore the lifter, if it is sticking; otherwise, you may need to replace the lifter(s).

How to Find a Noisy Valve Lifter

On some vehicles, removing a valve cover to locate a noisy lifter is not too difficult. To identify the problem lifter, you can use a mechanic's stethoscope, but a piece of rubber hose can work fine too.

  1. Remove the valve cover.
  2. Set the parking brake and the transmission to Neutral (manual) or Park (automatic).
  3. Start the engine and let it idle.
  4. Put one end of the hose against your ear and move the other end over the valve spring area of each valve.
  5. The lifter that is causing the noise will sound louder when you place the hose over the valve with the failing lifter.

You can use this method to locate valve train noises coming from a particular cylinder as well.

Rocker arms can also suffer from lack of oil.
Rocker arms can also suffer from lack of oil. | Source

V. I Can Hear a Rattling Noise

Just like worn valve guides, stems and springs, worn rocker arms are rare, unless they've been in service for quite a long time, there are problems in the lubrication system, or the system has been neglected.

Although a worn rocker arm most likely won't affect engine performance, it can cause valve train noise. You may hear a light tapping or rattling noise coming from one or more of the affected rocker arms.

To diagnose the problem:

  • Check the engine oil condition.
  • Check for proper oil circulation around the valve train.
  • Identify the noisy rocker arm using a mechanic's stethoscope or rubber hose as described in the previous section.
  • Remove the rocker arm and check for indentation or rough spots at the point of contact with the valve or, if applicable, the push rod.

Any of these problems can shorten the service life of a rocker arm, if they cause a lack of proper lubrication, or a widened clearance between the rocker arm and valve stem.

Too much valve clearance will cause a noisy valve and speed up valve stem and rocker arm wear.
Too much valve clearance will cause a noisy valve and speed up valve stem and rocker arm wear. | Source

VI. I Hear a Tapping Sound

A worn valve guide or stem is more common on high-mileage engines. Wear increases the clearance between the valve stem and the guide. With a wider clearance, oil will run along the guides and down into the combustion chamber.

Common symptoms include:

  • Tapping noise as valve rocks
  • Spark plug fouling
  • Abnormal oil consumption

If engine oil contaminates the spark plug electrode end, this can also lead to cylinder misfire.

How to Check for Worn Valves or Stems

  1. Remove the valve cover
  2. Pry on each valve sideways using a large screwdriver.

If you are able to move one or more valves from side to side, you'll need to remove the head for guide or valve repairs.

Timing belt or related components problems affect valve train operation.
Timing belt or related components problems affect valve train operation. | Source

VII. My Engine Has No Power

Problems with a timing belt or a timing chain may cause the engine to lose power.

Timing Belt Problems:

The most common timing belt failure is a broken belt because of prolonged service life, or a related component failure.

However, a worn timing belt can also stretch too much, or a failed component may cause the belt to skip a sprocket tooth. These problems may cause engine performance issues like:

  • Engine knock or ping
  • Increase in fuel consumption
  • Retarded ignition timing
  • Engine power loss

If you have an interference engine, a broken timing belt can wreak havoc with your engine. The best preventive measure is to replace the belt at the manufacturer suggested interval.

Timing Chain Problems:

A worn timing chain is not common, but it can happen on high-mileage engines. However, some timing chain assemblies use a hydraulic tensioner and guides made out of nylon.

It's more common for a hydraulic tensioner or the guide to cause problems due to dirty oil, lack of oil, or low system pressure. Although low pressure may cause noise along the valve train as well. Also, the guides can wear out to the point the tensioner is unable to hold the chain tensed.

Any of these problems will cause a slack on the chain between the camshaft and crankshaft sprockets. Besides a rattling noise, this will upset timing, preventing valves and pistons synchronization, and loss of engine power.

How to Check for Slack in Your Timing Chain

Besides diagnosing a rattling noise coming from the front engine cover, you can do the following check.

For this test, you'll need to remove a valve cover to gain access to the valve train, or, if your model has a distributor, remove the distributor cap.

  1. If your vehicle has a distributor, remove the distributor cap; otherwise, remove the valve cover.
  2. Remove the spark plugs to make it easier to rotate the crankshaft, if necessary.
  3. Using a socket of the appropriate size and a breaker bar, rock the crankshaft back and forth a few degrees, using the crankshaft bolt at the front of the engine.
  4. If the crankshaft moves a few degrees without moving the distributor rotor or valve, either the timing chain, the hydraulic tensioner, or the guide has failed.

A broken timing belt can cause severe damage like bent valves.
A broken timing belt can cause severe damage like bent valves. | Source

VIII. Preventing Valve Train Issues

Valve train issues may come in the form of noises, smoke, or engine performance problems.

Unless your engine has logged too many miles, most valve train problems will come from maintenance-related issues like lubrication system problems or misadjusted valves.

But keep in mind that even relatively simple issues can turn into expensive repairs if left unattended for a long period.

Start by taking care of the problem with the help of this guide and restore valve train and engine power.

To prevent common valve train problems, change the engine oil at the recommended intervals, and make valve adjustments as necessary. Consult your repair manual.

If you don't have the repair manual for your particular vehicle model, you can buy a relatively inexpensive aftermarket copy from Amazon. Haynes manuals come with step-by-step procedures for many maintenance, troubleshooting, and parts replacement procedures. So the manual pays for itself soon.

Questions & Answers

    © 2018 Dan Ferrell

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