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Old 12-15-2002, 02:49 PM
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Unhappy valvetrain problems

Ok I need everyones collective wisdom once more. Three months ago I put a Lunati 490 lift 292 duration cam in my 77 T.A. It is a 400 engine. In the last 2 months it has bent both pushrods on the #3 cylinder three times, only the #3 cyl. I set the valves 1/4 turn past zero lash. And if you are wondering,(like I did) no the valves are not sticking. I just removed the head today and there is nothing in the cylinder that would cause the valve not to open. And there are no marks on the piston and the valves to indicate a clearance problem. Any help here would be much appreciated. Thanks in advance. <img src="confused.gif" border="0">

[ December 15, 2002: Message edited by: pontiac man ]</p>

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Old 12-15-2002, 04:12 PM
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Maybe you gotta mixed up rocker ratio problem that causes the retainer to hit the guide, or maybe a bad lifter thats gone solid on ya. Roll the motor over statring fronm the Tdc on three and check the clearances every few degrees of crank rotation. I'll bet you find it then. Not enough tolerances that is.
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Old 12-16-2002, 03:49 AM
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I agree, check all your tolerances and have you're springs checked for allowable lift - DON"T trust what someone told you. I made that mistake once and the springs would coil bind .015". Comp Cams makes a good spring set 988-16, which I just installed in my 455, they allow up to .600" lift. You want to have .075" travel left in you're springs at full lift.
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Old 12-16-2002, 04:39 PM
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Ditto on what 455Poncho said.
I was sitting here thinking of what causes a bent pushrod, and physically stopping one end from moving is all I came up with. Spring bottoms out, rocker wont go down anymore, pushrod bends or lifter collapses.

I'll bet that all the others are close to bending on ya too. You already have a head off, might as well get them hopped up a bit & make them able to handle that cam. Good luck!
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