spotty valve deposit

[AC sports]

What do you make of these deposits?
Only on one inlet valve.
Only a spot on the back of the valve.

[Carnut1]

Coked oil from guide clearance.

[AC sports]

Yes. Ok. Should have made myself clearer... why only that one spot? I guess the valve doesn't rotate then, so would the guide bore not be perfectly round? .

[Carnut1]

That may be. Fuel wash may be enough to keep the oil off so the heat does not coke it.

[Newold1]

Is this the same engie that bent all those exhaust valves?

[ProPower engines]

What do you make of these deposits?
Only on one inlet valve.
Only a spot on the back of the valve.

From this pic it appears to be running down the stem.
You may also have a hot spot in that 1 chamber or high temp overall.
the single spot may be just the hottest part of the valve and the rest is washed away by fuel but that looks more like an oil and fuel deposit from the depth of it.
JMO

But regardless if the others don't show this a guide issue is apparent and needs attention

[AC sports]

Makes sense. This is the same engine that bent the exh valves. Actually all the inlets display it, but minimal compared to this one, which is quite obviously a spot section.

[Newold1]

From the problems in this engine with valves it looks like in the future and new builds you might have to spend more time on setting up the cylinder heads with better valve guide install and fitment. What type of valve seals does this engine use?

[AC sports]

I've built quite a few of these and never had an issue. They are a very robust engine. I'm going to revisit the valve guides. They run a standard type push on seal both on exh and inlet.