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Author Topic: Valve stem failure  (Read 3724 times)

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CDXXVII

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Valve stem failure
« on: August 19, 2013, 09:29:14 PM »
All new exhaust valves and one of them has gotten peened over by the rocker arm after 120 miles of street driving. Nothing radical in the valve train (stock LR cam/stock valve springs). Most likely a heat treat problem. Not sure if I should pull both heads and scrap all eight.
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jayb

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Re: Valve stem failure
« Reply #1 on: August 19, 2013, 10:32:51 PM »
I agree that it is a heat treat or hardening issue; I had that happen once to one of my engines and that was the general consensus for cause.  Unfortunately the valves go through the heat treat process in batches, not one at a time.  There's a good chance that more than one valve could have this problem.  I'd replace all eight; why take chances...
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Jay Brown
- 1969 Mach 1, Drag Week 2005 Winner NA/BB, 511" FE (10.60s @ 129); Drag Week 2007 Runner-Up PA/BB, 490" Supercharged FE (9.35 @ 151)
- 1964 Ford Galaxie, Drag Week 2009 Winner Modified NA (9.50s @ 143), 585" SOHC
- 1969 Shelby Clone, Drag Week 2015 Winner Modified NA (Average 8.98 @ 149), 585" SOHC

   

machoneman

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Re: Valve stem failure
« Reply #2 on: August 20, 2013, 06:12:32 AM »
2X on faulty heat treat. Can't see from the pic if you have adjustable rockers but......one could use a thin lash cap as a potential fix, drive it and check again if more valves show wear signs. It's a cheap, easy and quick fix but I'd only do so if one is hard up for bucks. Me, I'd replace all eight and sleep well  :) 
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Bob Maag

CDXXVII

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Re: Valve stem failure
« Reply #3 on: August 20, 2013, 06:53:02 AM »
Yes, adjustable rockers. Bucks is not a problem but time is. Maybe a temporary lash cap so I can drive the remaining two months of the season. (I live in the north.)  Then, if other failures show I will know better where I stand when I pull the heads this winter. More time in winter for these projects.
 Who has the lash caps?
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machoneman

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Re: Valve stem failure
« Reply #4 on: August 20, 2013, 06:56:15 AM »
Comp, Crane, etc. at Jegs, Summit.  Also sold individually, just get the right size for your stem and try to get the thinnest one (>than .080 if available).  Maybe someone here can send you one.

http://www.summitracing.com/parts/cca-621-1?seid=srese1&gclid=CJOfl4j8i7kCFa87MgodbTEAzQ

http://www.jegs.com/p/Comp-Cams/Comp-Cams-Valve-Lash-Caps/753205/10002/-1
« Last Edit: August 20, 2013, 07:08:00 AM by machoneman »
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Bob Maag

CDXXVII

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Re: Valve stem failure
« Reply #5 on: August 20, 2013, 05:14:38 PM »
Stem diameter is stock 0.371"
Lash cap 0.371-0.375" would work.
Anybody have a loose one taking up space?
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Qikbbstang

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Only problem I see driving it with lash cap a few months is --- what part of the
« Reply #6 on: August 22, 2013, 11:34:02 AM »
valve is that keeper holding on to...Kind of to close for comfort.............
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CDXXVII

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Re: Valve stem failure
« Reply #7 on: August 22, 2013, 09:30:28 PM »
Thanks. The keepers would not be effected unless they come in contact with the lash cap. I would have to make sure it does not.
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