Yes, AMC heads have this problem of the keepers touching each other and not
holding the stem well, and in time the stem will wear to the point of
failing.
I usually just put the keeper in the vise and use a small angle grinder to
take off enough that will make a gap.  I think, if I remember it right, only
needs 0.3mm to be taken off from each keeper.
I have seen valve stems that are totally useless and the valves had to be
changed.
Zoltan

----- Original Message -----
From: "John Rodgers" <inua@CHARTER.NET>
To: <vanagon@GERRY.VANAGON.COM>
Sent: Tuesday, October 31, 2006 4:29 PM
Subject: Re: AMC heads (part 2)

> Ben,
>
> Interesting stuff on your website.
>
> Before I get into this, let me say I AM NOT by any means an auto
> mechanic, not even close. So what I have to say may not even be quite
> right or even have application to an automotive engine. Guys (and gals)
> who work them all the time know what is what.
>
> I come from that aircraft mechanic perspective. I was taught on piston
> aircraft engines the critical nature of valve specs to the engine, it's
> operation and longevity. In that training we were taught that the intake
> valve was cold, the exhaust valve was hot, and that told the tale.
> Exhaust valves suffered a lot from the heat of combustion, because they
> didn't have the benefit of the cooling of the fuel-air charge coming in
> past it for combustion as with the intake valve, but the exhaust valve
> got the full brunt of the heat of the burnt fuel going out of the
> cylinders. Thus it was that often exhaust valves stems were sodium
> filled to help transfer some of the heat up the stem to the oil
> circulating around the cylinder top. The sodium would get hot, liquify,
> and slop back and forth in the valve stem first toward the valve face,
> then to stem end, each time transporting heat from the face to the stem
> end protruding into the circulating oil system.
> Crucial to the life of a valve was the alloy. It has to be tough, hard,
> and capable of transferring the heat. Also, such was the case for the
> valve seats to take the hammering they get under extreme conditions.
>
> On the aircraft engines, it was also crucial that the valve face and
> seat be ground to mate properly. "Properly"  for an aircraft engine was
> a valve face ground  with three different facet angles on it, and if I
> recall, the valve seat was similar. The real trick was to hand "lap" the
> seating surface of the valve face to the seat. Very fine grinding
> compound in a moderate lubricant was applied lightly to the valve face,
> and then with the head at the right angle so the valve stem would be
> vertical to the floor, a tool was used to rotate the valve back and
> fourth 90-180 degrees. The valve was then lifted, rotated 90 degrees,
> then set back in place, and oscillated back and fourth again. This was
> continued until there was a continuous, non-metallic-glistening lapped
> circle of the ground surface on the valve face and on the valve seat.
> The "lap-line" was specified to be approx 1/8 inch wide, and located in
> the center of the center third  of the ground valve face. .  The final
> test of the proper seat was to remove the valve, wash of all grit,
> re-insert the valve in to the valve guide - with out benefit of springs
> to seat the valve, The weight of gravity provided the force of the seal
> between valve and valve seat. The cylinder was then filled with
> gasoline. If the gas did not leak, then the work passed the test. If the
> gas leaked, woe be unto us  - we got our fannies kicked., an "F" for our
> grade, plus the luxury of doing a re-grind to get it right.
>
> I don't know if auto shops go to this much trouble for car engines. For
> an airplane, you had to have it right. It's a bit difficult to park on a
> cloud when there is a malfunction.  But I think if auto work was done
> with such attention to detail, a lot of our V-gon problems would
> disappear. To me, a proper valve job would include hand-lapped valve
> seats. It would involve also a check  to ensure no variation in the
> length of the valves - even new valves.
>
> Ben, a question(1)
>
> Can one take those valve stem retainer halves  and simply grind them
> down on a surface plate with 400-600 grit wet/dry paper and take off
> enough to get them to fit with the tiny gap-o-sis that is needed??
>
> Question (2)
> Do you know what metal is used for the valve guides in todays
> engines.Aircraft engines use to use bronze guides. That may have changed
> by now. Curious to know about modern auto engines.
>
> Regards,
>
> John Rodgers
> 88 GL Driver
> Chelsea, AL
>
> Benny boy wrote:
>> So lately i have worked on some engines with somewhat old AMC heads... so
>> of
>> course, i have seen other scary stuff... after some e-mail exchange with
>> Bob
>> Donald about those problems... i have uploaded my page to show you how
>> bad
>> AMC valve are... or can be, because it's not always the case, that is the
>> real main problem!
>>
>> http://www.benplace.com/amc.htm
>>
>> Cheers, Benny boy (working like a dog)
>>
>>
>>
>
>
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