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Broken Valve Spring
I have a Superformance cobra, built in 1996, with a 460 crate motor. This past Saturday, I was pulling into my neighborhood and I heard a terrible noise. I limped it a few hundred feet to get it into the garage. After some diagnosing, I found a completely shattered valve spring, maybe 7 or 8 pieces. I was able to find the keepers and what was left of the seal. I have some new springs and seals on order. My biggest concern is that I can’t get the valve to move. It appears to be in the closed position, with everything off of it (rocker arm and spring seats removed), but I can’t get it to budge even the slightest bit. I have given it some light taps with the lead hammer, but it seems pretty stuck. I guess my main concern is if the valve could have bent, below where it sticks out of the head. Has anyone experienced anything like this?
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Does the valve stem align with the rocker arm - if not, that would seem to be a good indicator of a bent stem? I would think the pushrod would be severely bent too though.
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A valve that seems to be in the closed position is unlikely after a valve spring breaks. |
Well, its a good chance the top of the piston is damaged too. I'd prolly remove the spark plug and look around in the combustion chamber.
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For me, every engine failure was an opportunity to upgrade to better parts.
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As mentioned, the valve probably kissed the piston and bent the valve stem when the spring broke. You may have piston, block and cylinder head damage. You'll have to pull the offending head and inspect for damage.
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for indications of obvious damage but as Undy stated you're looking at pulling that head to be sure. |
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If the heads are not ported or otherwise modified the cheaper way home might be to just buy a replacement casting and move your stuff to the new head. Have a valve jbb done and put it back together. Ed |
For my own curiosity and the OP, what is the likely root cause of a bent valve?
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Generally - valve float, valve spring harmonics, and then contact with a piston. I have had twin cam 16v engines with ALL 16 valves bent. |
Working on removing the head. Got the exhaust and carb off. I took all of the bolts out of the intake, but it is a little stuck on. I figured it was a good spot to stop. I’ll report back when I get the head off.
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Ed |
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Ed |
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A valve head has to contact the piston to be bent. This could occur at ANY engine rpm, either from valve float at high rpm, or from valve spring failure, which could happen at the next startup, idling etc. In the owners case, the valve spring has broken into many pieces, the valve drops to full open, the moving piston smacks the valve head, and keeps smacking it until the valve head snaps off, wedged into the valve seat. 50% of the time the piston could be damaged, especially from large valves. |
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I was able to remove the intake and all 10 of the head bolts. I can definitely see a bent valve from the intake port.
I haven’t figured out how to get the head loose. Any ideas? |
Refit 2 head bolts, one each end, at about 4 threads in.
Refit the spark plugs for that head, leave the other bank out. Spin the engine on the starter. Head should break from the headgasket. Otherwise, a large prybar, waterpipe etc down the intake port, and pull over. |
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This picture is exactly what Gary described / predicted in post #15. Ed |
Do it manually with a pry bar. Don't attempt to spin the engine, you already have damage and don't want to make it worse. Just make sure you have ALL the head bolts removed. Good luck.
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2021-10-17 Edit: 460 CID standard bore is 4.36", so (4.36 ÷ 2)² x 3.14159 = 4.7524 x 3.14159 = 14.93 in² x 100 PSI = 1,493 lbs. My earlier numbers were incorrect. |
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