Chipped valve

[mini64]

Chipped exhaust valve took me out of the races the other week. I assume I over revved him and slapped the piston with the valve but there is no evidence.

[bitsobrits]

Are you sure it's not just an extremely burned valve?

If a piece of the valve that large actually broke off (and presumably exited via the exhaust), you would be able to see mucho telltale marks in the piston crown and cylinder head.

[rgh0]

Check if the valve stem or head is bent, if you hit the piston you normally put a bend in it. Been their done that

A small bend can lead to exhaust gas leakage past the valve and seat. These hot gases can rapidly burn out the valve like you appear to have.

Clean the valve and check the face of the fracture with missing bit. If its a fracture that will be obvious versus a oxidation burnt surface.

Even a small leak due to wear and without hitting the piston ( or other valve) and bending the valve can lead to a valve burning out rapidly. Lean mixtures and over advanced ignition and loose exhaust stem clearances and poor conductivity valve guides can also contribute to or cause the problem especially in a race engine with constant full throttle high rev use.

cheers
Rohan

[Chancer]

Agreed, its burned out, check the seat insert very carefully for damage or cracking.

[The Veg]

You got off easy.

This happened to a BMW motorcycle I owned back in 2007:

[mini64]

seems I had no idea what a burnt valve could look like. googled it and found many valves looking like mine. Sure enough the "fracture surface" on mine didn't look like a fracture but indeed almost like a torch cut surface!

Valve measures straight and seat looks fine. Valve seems tight in guide. I don't believe I have lean running or advanced timing issues but will recheck when all is back together. maybe it's just time for a head rebuild? Any opinions on the below cylinder head photos?

number four cylinder with burnt valve:

number 1

number 2

number 3

[Bud English]

Why is the spark plug in the #3 position so recessed? Just not tightened in?

[mini64]

Correct-plugs loose

[rgh0]

It looks like something small went through the cylinder with the failed exhaust valve from the dings in the cylinder head. This may have been a bit of the failed valve or it may have been something else that caused the valve to fail.

It may have been a bit of broken ring or an electrode off a spark plug or something small that came in the inlet. Worth a look around to see if you can find where it came from.

cheers
Rohan