Exhaust Valve

[jpian0923]

Here is a picture of my Cylinder #2 exhaust valve. What would cause this?

[Dave Neptune]

Many things?

Jim, it may be nothing and it may be burned. I have often see where a mechanic has ground off the edges of a burned vale that has cleaned up when regrinding the seat. Often there will be a slight crack forming at the edge and it is just ground away. Not all that uncommon in flatheads.
What is more important is how the seat in the block looks. Is it rusted out underneath or just a good seat.
Were you loosing compression? Could also be caused by the exhaust valve hanging up a bit or even way out of adjustment. This would keep the valve just slightly open enough to burn.
Could also be a bit of a bent valve causing a burning too.

Get a pic of the seat and was the valve adjusted OK?

Dave Neptune

[hanleyclifford]

It almost looks like a brazing repair has been made to the block. The damage appears mechanical, not corrosive; there could be a small crack adjacent to the damage. Suggest you remove the gasket carefully looking for possible water migration. Very curious. Please post more pictures.

[jpian0923]

I had compression of 40 to 45 psi in cylinder 2. It was over 100 in all the rest.

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I had thought it was the rings.

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There is no damage to the head.

[hanleyclifford]

Did not expect damage to the head but it will be interesting to see that valve seat once the valve is out. That valve looks battered. Can we see the other side where it is faced?

[Loki9]

That looks like a burned valve. One cause is a failure to rotate as it lifts. That can be caused by a worn cam shaft or a stuck (from rotating) lifter.

[Al Schober]

Not a biggie, assuming you can get the block to a shop where they can install inserts for the exhaust valves. Last block I did apparently didn't clean up well when they were doing the exhaust seats, so they installed 4 hardened inserts without even asking me. No extra charge vs the quoted price for grinding the seats. If you can't find a valve, get back to me - I'm sure I've got an extra in a coffee can in the garage.

[jpian0923]

Does this look like normal operation?
The valves all seem to go up and down freely and go up about the same height.
I don't see any of the valves rotating. Should they?

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Everything seems normal here as well. The tapets rotate freely when its corresponding cylinder is at TDC.
The gaps are not too far off either.

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Can you tell anything about the seat, or do I need to clean it up a bit?

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[jpian0923]

Why so much carbon?...and how can I prevent that in the future?
Seems to me that all that carbon can really foul up the normal operation of an otherwise healthy engine.

[hanleyclifford]

Carbon build up can be caused by running too cold (anything below 160 is too cold IMO). It is also caused by running too rich and in some cases by worn rings or valves. The valve stem OD should be measured as well as the valve guide ID to see if the clearance is within tolerance; in this case I doubt it. If you have a big set of drill bits (129) you can get a decent idea of valve guide ID by trial and error until you try to insert a bit that won't go in.

[Loki9]

The valves should rotate when the engine is running, they probably won't when turning it over slowly. They only turn a few degrees per lift.

[jpian0923]

Jeff,
Would you attribute the lack of valve rotation to carbon build up or to a bad valve and seat mate? Or to a worn guide? Or to all of the above?

Haven't had time to remove all the valves but once I do I'll give everything a good cleaning and inspection. Hoping to only replace the bad valve.

[hanleyclifford]

As you remove the valves make sure you have a system for keeping everything organized so all components stay with their respective holes. I hope you will post several pictures from different angles of that valve. It's very curious looking. Also a picture of the valve chamber looking straight down ito it.

[Loki9]

Jeff,
Would you attribute the lack of valve rotation to carbon build up or to a bad valve and seat mate? Or to a worn guide? Or to all of the above?

Haven't had time to remove all the valves but once I do I'll give everything a good cleaning and inspection. Hoping to only replace the bad valve.

Hard to say, but check that everything is clean a moves easily. The rotating comes from a slight angle on the lobe of the cam shaft that presses on the lifter off center. The lifter rotates and in turn rotates the valve. It only works well at elevated RPM, often there is little or no rotation at idle.

[hanleyclifford]

Hard to say, but check that everything is clean a moves easily. The rotating comes from a slight angle on the lobe of the cam shaft that presses on the lifter off center. The lifter rotates and in turn rotates the valve. It only works well at elevated RPM, often there is little or no rotation at idle.

It would be a first in my experience on an A4 but this introduces yet another twist to the question. Perhaps the camshaft lobe lift should be checked by manually rotating the engine and measuring (spec is .239" lift).