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Old 06-05-2010, 06:36 PM
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SBC valve tips mushroomed

I bought a set of 416 heads for my 283....after getting them home and looking at them I discovered that one of the heads has 3 exhaust and 1 intake valves where their tips (end that touches lifter) is mushroomed.....like someone to a ballpean hammer to them. The guy said that he had set them up for .500 lift and that he had ran the least lift Voodoo cam for a couple thousand miles. (.437" / .454" lift).
So whatcha think caused this?

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Old 06-05-2010, 07:27 PM
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Valves installed at the wrong height and not corrected with the proper pushrod length can cause this.

Also, stem tips are generally case hardened to prevent mushrooming of the tips by the rockers. If the valves have been ground down in an attempt to get the installed height correct, the grinding may have removed the hard casing of the tip and allowed the rocker to mushroom the softer material underneath the case hardened outer shell.
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Old 06-05-2010, 07:55 PM
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A bad rocker arm can also cause this. Tho most of this type of damage I see is on high mileage truck motors. That have worn thru the rocker arm hardness.

I have seen regular and long slot stamped rockers that have been exposed to weak springs, excessive RPM. Incorrect geometry, bind or just worn out to begin with. A lot of guys don't check the contact area or don"t know what to look for...

If installed on good valve tips, the worn out piece will smear the tops and mushroom the tops or round them over.
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Old 06-05-2010, 07:59 PM
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A valve job that neglected to reheat treat the tips will do what you've described.
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