This auto repair article is about engine valves and some of the common problems they can cause. Also provided will be an overview of common symptoms and solutions when an engine is having a problem with intake or exhaust valves.
The main function of an engine valve is to open and close rapidly. This allows the air/fuel charge in and after combustion allows the exhaust gases to flow out. 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 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.
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 leading to an 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.
When it comes to engine smoking this can be caused by engine valves but also other parts like worn piston rings. When blue smoke is seen on start up on a cold engine most often you can pin the problem on excessive valve guide clearance or worn valve seals.
If the engine smokes all the time or on heavy acceleration the problem is more likely to be the piston rings. In both cases I recommend professional diagnosis and if possible a second opinion before spending a lot of money on large engine repairs.
Engine valve seals can be inspected for wear and condition. The stem to guide clearance can also be measured and compared to 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.
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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.
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link will take you to the homepage from this article about engine valves.