Exhaust valve stem wear, why?

[JPSTANG]

Havent posted in a while so here goes.
Went in to do valve guide seals cause I would get the blues after decelerating and stepping on it again or long time under manifold suction like going slow up my road.

Read on here about another guy that had somewhat the same issue and his seals were different looking than stock, larger center. Decide it was worth a look at mine.
Think I figured out why his were that way, see the attached pictures and give me your best guess why it would wear only at the top like this. And it is only the top where the seal is at, rest of stem is shiny new, but loose in the guide. Effectively it chewed the seal lip away and caused it to leak.
Little more back ground for the best educated guess. Yes my cats did get partially plugged, they r gone now. Yes I did have knock, but these valves where on only 3 cylinders 2/7/8. Compression was good across the board all numbers between 210/215.
Thoughts?

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[Mad Horse]

Have you run a fingernail over the damaged part of the stem? Could it just be seal material that has attached itself?

 

[JPSTANG]

Yeah it actually took the chrome coating right off, just at the tops.

 

[GT Pony]

Yeah it actually took the chrome coating right off, just at the tops.

Are the valve stems actually chrome plated, or are they just stainless steel?

If only a few valves showed this wear, I'd say it was a manufacturing flaw - like a badly reamed/finished (not smooth enough) valve guide that caused abnormal wear that just kept getting worse with more miles.

 

[JPSTANG]

They appear to be chrome plated to me. But I guess not quite sure now that you ask. Just wierd if most people's oil consumption problems would be also attributed to this and they never know. I didn't have oil consumption all that bad though.

 

[GT Pony]

They appear to be chrome plated to me. But I guess not quite sure now that you ask. Just wierd if most people's oil consumption problems would be also attributed to this and they never know. I didn't have oil consumption all that bad though.

Could just be a badly galled up surface, and it makes it look like there was some kind of metal layer on the stem - ??

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