This auto repair article is about engine valves and some of the common problems they can cause when something goes wrong with them.
Learn how overhead systems work and see how to address noise, engine misfires and smoke problems when they go bad.
Also provided is an overview of the symptoms and solutions for when an engine is having a problem with an intake valve as opposed to an exhaust valve. These conditions have a completely different set of symptoms.
How the Valves Work
The main function of an engine valve is to open and close rapidly. This allows the air and fuel charge inside the combustion chamber and after it’s ignited the exhaust valve allows the waste gases to flow out.
The engine can’t inhale and exhale unless the valve opens and closes at the right time. If you need any further explanation of how this 4 stroke process works I provide more detail about the individual cycles on my page about how engines work.
Depending on your age you may remember that back in the day it was common for the local auto repair shop to say, “hey you need a valve job”. You do not hear this as much today.
This is because of the improved manufacturing process and tighter tolerances on modern engines. Regardless, if you put enough miles on even a modern engine you might experience a problem with the valve train.
Noise or Tap Valve Train Problems
Some of the more common problems people experience with engine valves would be noise and smoke.
Often when you hear a ticking noise from the engine a mechanic will tell you that this is a valve tap. If the upper end of the engine becomes noisy it could be due to inadequate lubrication.
This can be caused by low oil pressure, but also obstructed oil passages due to engine sludge or poor maintenance.
The main reason that a valve tap should not be ignored is a lack of lubrication issue could cause rapid stem and valve guide wear. This could eventually lead to engine failure. This is why when an upper engine noise surfaces it usually doesn’t get better it gets worse.
If the engine valve tap is addressed quickly low oil pressure problems can be solved.
In some cases replacing a worn-out oil pump does the trick. If the tap is caused by lack of maintenance and restricted oil passages (depending on the severity) this could also be turned around.
Cleaning the oil pick up screen with either engine flushes or better yet physically cleaning it by removing the pan can help. Also the oil lubrication galleries can be cleared with mechanics wire and solvents. When full lubrication is restored the engine might be saved.
Worn Valve Seals and Blueish Smoke
When it comes to engine smoking issues, it can be caused by engine valves, but also other parts like worn piston rings.
However, when you get a puff of blue smoke that’s seen on cold engine start up, most often you can pin the problem on excessive valve guide clearance or worn valve seals.When I say puff, I mean it only smokes a short period of time.
If the engine smokes all the time or on heavy acceleration the problem is more likely to be worn piston or oil control rings. This condition is confirmed with a wet and dry compression test.
However, in both cases, I recommend professional diagnosis. And if possible a second opinion before spending a lot of money on large engine repairs.
You can inspect engine valve seals for dry rot, wear and condition. You’ll also need to measure the guide clearance with a dial indicator and compare this precise measurement to manufacturer specifications.
If the clearance is too great, oil can be drawn down both the intake and exhaust valve guides and burned in the combustion chamber with the air/fuel charge causing a bluish colored smoke from the tailpipe.
As far as the solutions for smoke problems, if they are pinpointed to valve train issues they can often be solved without engine replacement. In fact in the case of worn valve seals they can be replaced using special tools without even removing the cylinder heads.
If it turns out that the smoke problem is related to excessive valve guide to stem clearance a short-term solution can be applied known as knurling the valve guides.
Knurling of valve guides is a process for restoring the proper clearance. A special tool is used that physically cuts into the guide and metal is raised up on either side of the tools cutting blade.
This actually decreases the inside diameter of the hole that the valve fits in. Then a finishing tool flattens the new ridges so the engine valves move smoothly in their bores.
Back in the old days many auto repair shops performed their own valve jobs and machine work. Today it is more common that the auto repair center will remove the cylinder heads and send them out to a specialized shop that performs the actual repairs.
In either case there can be skill involved and human error can reduce the longevity of the repairs. If you have a valve job performed it’s nice to know what kind of warranty the maintenance center and or machine shop will provide to cover workmanship.
Intake Vs Exhaust Valve Problems
When an engine valve is damaged and is no longer sealing off the combustion chamber we consider the valve burned. It gets this nick name, because when you take the engine apart you’ll often see heat damage.
When you have a burnt valve it will make a popping sound on the combustion stroke of that cylinder. You can tell if the burned valve is on the intake side or exhaust side by where the popping noise is heard from.
If it pops out of the exhaust system tail pipe its an exhaust valve issue. If the pop sound is heard better through the throttle body in the engine compartment, then the intake valve is the cause. You can isolate the cylinder by performing a compression test. The cylinder with the problem will have much lower compression then the healthy cylinders.
Although I wouldn’t consider engine repairs a good project for the driveway mechanic learning more about the process can help you negotiate with the repair shop. I have about 10 more pages on the subject of understanding and testing automotive engines that might help.
Hows this for an interesting idea? Build your own scale plastic working car engine model and you’ll completely understand how a motor works by the time your finished.
If you would like to learn more about the you fix cars website this next link will take you to the homepage from this article about engine valves.