Burnt valve

[m_wnzl]

What exactly does a burnt valve look like, and can it be reused if you lap it?

[96paseo]

Typically whitish-yellow appearance and coarse feel on the lip where it meets the seat. The valve themselves aren't all that expensive but the getting the head checked and re-worked is what is. Re-using the old one is not a good idea.

[sam333]

Its very common to have a peice missing from a burnt exhast valve.

Sometimes a pie shaped section will be missing from the head of the valve and you will have zero compression on that cylinder.

When you remove the valves they are always dirty and encrusted with carbon ( even when the valves are good).

What separates a burnt valve from just wear ,is on a burnt valve the damage is done by hot gases( exhast gases) eroding the valve.
Not having your valves adjusted properly is one common cause.

When they are too tight they dont rest long enough on the valve seat( that helps cool the valve through conduction) and they overheat and fail.