I’ve asked a few engine builders over the past couple days and one seemed confident that the pitting is caused by the stem seals leaking and oil running down the valve, then burning and “sticking” to the exhaust valve . It makes sense, as the #2 cylinder in her car also had the most evidence of valve seal leakage.
Why do valves pit?
The intake valves run cooler because the air and fuel sucked into the engine before the compression stroke cools them down. ... It can also be caused by excessive valve lash that slams the valve down hard as it closes.
What does pitted valves mean?
Burning and pitting are generally caused by the valve failing to seat tightly, permitting exhaust blow-by . This condition is often caused by hard carbon particles on the valve seat. It may also be due to weak valve springs, insufficient tappet clearance, warpage and misalignment.
What can cause a burnt exhaust valve?
One of the most common burnt valve causes is an ineffective seal between the valve and valve seat . Burnt valves occur when the valve can no longer seal correctly after excessive temperatures have damaged the material of the valve. When this happens, combustion gases are able to escape.
What are the symptoms of a stuck exhaust valve?
Symptoms. Valve sticking will typically manifest as a clicking noise that regularly occurs every two to three seconds at idle . This noise may be especially pronounced at start-up when the engine is cold. In severe cases, the valve may hang open and cause a cylinder misfire or even hit the piston and damage the engine.
What causes a piston to hit a valve?
a valve could hit a piston because the timing is off and the volve doesnt close in time and the piston comes up and helps it ... a rough idle wouldnt cause that but try looking at all the valve springs, if one is broken the valve wouldnt spring shut but would be once again helped by the piston.
What could cause a valve stem to wear in one area?
Possible causes include an incorrectly set valve clearance − or the valve seat insert or valve guide were not remachined centrically. An excessively large or small valve guide clearance can also have fatal consequences.
Should you Lap new valves in old head?
New seats, with new valves should require no lapping to get a good seal – my machinist refuses to lap in the first place, considering it to be a half-baked solution.
How much does it cost to fix a burnt exhaust valve?
How Much Does it Cost to Fix a Burnt Valve? Replacing a burnt valve (or the entire cylinder head) is a costly and labor-intensive repair. If you choose to have a professional do the job, you can usually expect to pay somewhere between $1,000 and $2,500 to get the job done.
What does a bad exhaust valve sound like?
A burned exhaust valve will often make noises that sound like a puff or putter. ImperialClub.com refers to it as a “chuff-chuff .” These sounds go off each time the cylinder tries to fire. ... If it gets sucked in every so often, it is likely a burned exhaust valve.
What is the most common valve failure that affects compression?
| A B | What is the most common valve failure that affects compression? Degradation of the valve face and the valve seat surface | why must the “charge” in the combustion chamber be compressed before ignition Improved vaporization of fuel and air |
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How do you free a stuck exhaust valve?
Hit the valve with a brass hammer, gently, trying to close it — exhaust valves always stick in the open position. This works well, but slowly. It could take days, maybe a week or longer. Keep soaking, tapping, and hitting until the valve breaks loose.
How do I know if I need a valve adjustment?
When do I need to have a valve adjustment? You should have your valve lash inspected at manufacturers recommended intervals. A sure sign that it’s time for a valve lash adjustment is if your engine is making a loud clicking or tapping noise when starting up or if you experience a loss in engine power.
Does the piston hit the spark plug?
Black95awd. please excuse the poorly drawn diagram, but as you can see there is no way (unless your piston is in pieces) that it will hit the plug. it may be out of time and hitting valves. If this is the case then you will have to replace valves because they will be bent.
