Broken Valve Spring

splenderleith · #1 (**permalink**) 10-10-2021, 06:44 PM

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?

DanEC · #2 (**permalink**) 10-10-2021, 07:57 PM

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.

Gaz64 · #3 (**permalink**) 10-10-2021, 10:27 PM

Quote:

Originally Posted by splenderleith

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?

Please post some photos of all valve stem heights with the rockers off.

A valve that seems to be in the closed position is unlikely after a valve spring breaks.

t walgamuth · #4 (**permalink**) 10-11-2021, 03:43 AM

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.

Tommy · #5 (**permalink**) 10-11-2021, 05:04 AM

For me, every engine failure was an opportunity to upgrade to better parts.

undy · #6 (**permalink**) 10-11-2021, 05:35 AM

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.

Unique427 · #7 (**permalink**) 10-11-2021, 06:09 AM

Quote:

Originally Posted by undy

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.

If you have access to a bore scope, poke inside the spark plug hole
for indications of obvious damage but as Undy stated you're looking at
pulling that head to be sure.

eschaider · #8 (**permalink**) 10-11-2021, 12:23 PM

Quote:

Originally Posted by splenderleith

...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. ...

It is called a bent valve. You will likely find the guide is damaged also and needs to be replaced along with the valve. You will also need to have the valve seat redone.

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

Tommy · #9 (**permalink**) 10-11-2021, 02:00 PM

For my own curiosity and the OP, what is the likely root cause of a bent valve?

Gaz64 · #10 (**permalink**) 10-11-2021, 03:35 PM

Quote:

Originally Posted by Tommy

For my own curiosity and the OP, what is the likely root cause of a bent valve?

Engine running, cheap valve springs. Doesn't need to be high rpm.

Generally - valve float, valve spring harmonics, and then contact with a piston.

I have had twin cam 16v engines with ALL 16 valves bent.

eschaider · #11 (**permalink**) 10-12-2021, 09:06 AM

Quote:

Originally Posted by Tommy

For my own curiosity and the OP, what is the likely root cause of a bent valve?

Contact with a piston.

Ed

t walgamuth · #12 (**permalink**) 10-12-2021, 11:56 AM

Quote:

Originally Posted by eschaider

Contact with a piston.

Ed

I would expect it was over revved. With all the rev limiters available today this is less likely but I would still think most common. It could be done by downshifting at too high rpm also.

eschaider · #13 (**permalink**) 10-12-2021, 05:13 PM

Quote:

Originally Posted by t walgamuth

I would expect it was over revved. With all the rev limiters available today this is less likely but I would still think most common. It could be done by downshifting at too high rpm also.

Best efforts not withstanding, sadly there is always a way to circumvent safeties we attempt to build in. That said, it does not matter how high you overspin the engine or even float a valve. If a piston does not hit the valve, the valve will not bend.

Ed

Gaz64 · #14 (**permalink**) 10-12-2021, 05:28 PM

Quote:

Originally Posted by eschaider

Best efforts not withstanding, sadly there is always a way to circumvent safeties we attempt to build in. That said, it does not matter how high you overspin the engine or even float a valve. If a piston does not hit the valve, the valve will not bend.

Ed

Yes, that is exactly correct.

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.

splenderleith · #15 (**permalink**) 10-11-2021, 07:05 PM

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.

ZOERA-SC7XX · #16 (**permalink**) 10-13-2021, 11:16 AM

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.

DanEC · #17 (**permalink**) 10-13-2021, 04:47 PM

He’s correct - just like a hydraulic brake line. 100 psi is 100 psi. The issue might be when it’s multiplied by the cross sectional area of the bore in square inches as cycleguy55 said.

eschaider · #18 (**permalink**) 10-14-2021, 12:00 PM

OP,

What you have here is commonly called a blown engine. By and large you do not want to replace just the broken parts with new good parts, that is a formula for follow on failure.

There is a good chance your engine will look similar to HTM101's when you finally get it taken down. If you have one dead piston when you replace just that one piston you could find it challenging to get it to the same weight as the other seven for balance purposes. The upshot is a new set of oversize pistons, pins and rings, boring the block, individually fitting each new piston to its new cylinder and or course rebalancing of the rotating assembly.

You can frequently that find shrapnel from the cylinder with the broken valve has found it's way to other good cylinders and done damage over there also. This would likely also require other pistons being replaced. Just buy a whole new set and do the job correctly.

When you finally get the head off, if the valve head has been pushed into the port throat damaging the valve seat, while repairable, the short way home could just be replace the old damaged casting with a new one. The exception to this would be a head casting that had significant additional work done on it for example like a nice porting job.

If you have a cracked or gouged cylinder you can certainly bore it and put a sleeve in it. For a high performance engine however, I might begin looking for a replacement block. For FE engines with all the availability issues they currently have, this will certainly become more challenging, especially in the current economic and supply chain impacted climate.

When a valve spring breaks there can be certainly two and sometimes three or more pieces. Your broken spring has many pieces. This could be an indicator that the engine was operated for some time after the initial break because the failure was not apparent to the driver. If that is the case then there is the possibility for broken spring pieces to have found their way into the oil system and done additional damage elsewhere in the engine.

Bottom line this is an R&R for the engine with a complete rebuild not just a cylinder head repair.

Ed

splenderleith · #19 (**permalink**) 10-14-2021, 06:05 PM

Still no luck getting the head to budge enough to get a plastic spackel knife under it. I am starting to lose confidence that I will ever get it off. I will try to get some thin hex nuts to get the studs out.

NROTOXIN · #20 (**permalink**) 10-16-2021, 02:07 PM

Quote:

Originally Posted by splenderleith

Still no luck getting the head to budge enough to get a plastic spackel knife under it. I am starting to lose confidence that I will ever get it off. I will try to get some thin hex nuts to get the studs out.

I'm looking at my car and without removing the 9/16 studs the heads cannot be removed due to foot box interference. Removing the 9/16 studs on the lower/back deck of the engine in the car appears very difficult to impossible.