If you start out with a pair of new heads and drive responsibly you can
get 140K out of a pair of heads.
I did and the 140K heads on my workbench still look pretty good too.
It takes a lot of abuse to overheat heads enough for valve seats to drop
out.
This event happens when the heads are overheated many times.
I've restored several type IV engines and if you've got dropped seats you
better check your ring lands and rod bearing on that cylinder.
I certainly cannot speak on rebuilt heads, I've always bought new AMCs
and never had any problems at all.
I bough my last set of AMC heads from  Gordon Johnsons Machine, 375 South
200 West, Bountiful, Utah, 84010.Call him at 801-298-2142. I can't quote
prices but he left me smiling.
I'll be glad to any discussion that may benefit you on the subject of Air
Cooled Type IV.

Stan Wilder
83 Air Cooled Westfalia

On Wed, 20 Feb 2002 17:30:58 -0800 John Tullier <elefntkpr@YAHOO.COM>
writes:
> For those of us with air cooled power plants, there is
> the valve seat issue.  Personally, I wouldn't mind
> hearing more about that one whereas I am currently
> holding one of my valve seats in my hand...I should
> rather it be pressed into the head honestly.
>
> Be safe and free of malfunction.
>
> John Tullier
>
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