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  #1 (permalink)  
Old 03-10-2019, 07:07 PM
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Default 427 broken valve spring

So I found this today, after ruling out spark and fuel on a dead cylinder.



What might cause such a catastrophic failure like this, so I can avoid it going forward?

It's been getting below freezing at night here, though I always let the car idle for 5-8 minutes until the water temp gauge starts moving, and never drive it hard until the oil temp is fully up.

I did have it in the shop over the Summer for some work which involved taking the valve train apart. Possibly damaged then or mis-installed? Seems like that would have happened much sooner if that were the case.

Hopefully, the valve is not bent.. or worse!
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Old 03-10-2019, 08:25 PM
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Was the top.of the valve peened over?
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Old 03-10-2019, 09:19 PM
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More importantly, who makes the valve springs?

A failure like tells me to throw all 16 (32) in the trash, and replace with a better brand to suit the camshaft.

Something is not right in the setup, too many coils clashing etc.

Gary
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Old 03-10-2019, 11:00 PM
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According to the docs that came with the vehicle, Competition Cams - though the part number no longer matches anything they sell today. The setup is 20+ years old, though had less than 5k miles on it.
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Old 03-11-2019, 12:11 AM
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@Moriaty, (Really sorry I missed your July PM last year, was really busy with our vintage race meet) we had the same thing happen last year, to a members Superformance (Roush 402? 408? SBF) He had driven his 300-400 since buying it, after it being in long term storage. After his valve spring failure, his mech. here in Silverdale Wa., said it was from just sitting, he replaced all the valve spring's and checked heads & piston's gave it a clean bill of health, no harm & foul. If you need his # (Mech) over here, or we have a "new" Shelby mech. here in Gig Harbor, but you have to get in line behind Brent's car, and mine Rob's (GH Mech.) GT-500 will be touring with us PNW members this year. Your more then welcome to join us, Cheers Tom. 360 801 4510.
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Old 03-11-2019, 04:14 AM
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Tom,

Your post reminds me that in race applications, which then might extrapolate to high performance street engines with similar characteristics, when you refresh your engine, the valve springs get replaced. When I brought my engine to Donahue Brothers it was not even a question on their mind, and the engine had 8 race weekends on it which is not a lot of hours and less than 500 miles, no matter what the springs look like they get replaced as sooner or later they will fail.

Prior to getting my MGB race car I was looking at an early 2000's Mustang race car that had been sitting for a couple of years, and even though it had been refreshed a couple of races before getting retired, the owner said that I should replace the valve springs as the valves that were open had been sitting under high tension for a few years and were bound to fail.

As Gary (Gaz64) said, put them all in the trash and get new ones. Hopefully no serious damage to the head, piston or block. Good luck.

Jim
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Old 03-11-2019, 06:49 AM
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If you take the pieces to a metallurgist, they can tell you the reason for the failure by looking at the fractures. There was probably an impurity in the spring wire which caused a stress riser and a failure.

I agree with others here that all springs be replaced. Hopefully your valves and piston are ok. Good luck.
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Old 03-11-2019, 06:50 AM
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What I'd be worried about and you mentioned is piston to valve contact. There's no way I'd just replace the springs and roll with it. The head would have to come out to inspect the valve/guide. A valve bent and weakened could have a catastrophic failure and pop the head off the valve. You might be replacing the entire engine then, not just a set of valve springs.
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Old 03-11-2019, 03:14 PM
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All the rocker gear needs to come off.

Straight edge across the valves, if the valve with the broken spring is down, the valve has kissed the piston, and the valve is bent.

A leak down test will also confirm this.

Then the head needs to come off.

Gary
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Old 03-12-2019, 04:25 PM
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Just like cam core suppliers, there are only a few credible valve spring manufacturers capable of making high performance valve springs. Almost everyone buys from them, rebrands the springs and markets them under their own naming convention. Two of the three big boys in this game are PAC valve springs and Associated Spring. There is actually a third supplier whose name my aging brain cells can't recall right now.

All three firms will build custom spring designs if you contract them to do so. The biggest problem with going down the custom spring path is that frequently the reason the original spring manufacturer does not offer the design is because current metals technology and heat treat will not reliably support the design.

In all probability the spring you have that failed, as others have already pointed out, either had impurities in the steel that initiated the failure or perhaps it was an il-conceived custom design that should never have seen the light of day.

As others have already suggested you should give serious thought to replacing all the remaining springs with known good alternatives. PAC will sell directly to you. Associated tends to be more of a high quality spring manufacturer whose business focus moves products through distribution under the name of a respected retail name.

PAC is the easy choice. There are a number of excellent aftermarket providers like Manley that provide high quality product. Interestingly the il-conceived custom springs are sold most frequently through a cam manufacturer. Buyer be ware ...


Ed
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Old 03-13-2019, 06:28 AM
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And sometimes even the big name springs break. This is a dual PAC spring that failed in my FE. The main spring broke into 3 pieces. The smaller spring held the valve in place. The valve train was well maintained. The spring had about 2800 miles on it. It is listed in the PAC catalog as a spring designed for high rpm use in circle track racing. Its use in my engine was 100% street driven with an occasional high rpm spurt.


Last edited by HTM101; 03-13-2019 at 06:33 AM..
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Old 03-13-2019, 09:17 AM
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HTM,

It's possible that a race spring may not have the fatigue life that a street spring does. Not saying that's necessarily the case with this particular one; it is a possibility.

Race springs are generally expendable - when you refresh the engine after what would be a very low number of miles compared with street use, the valve springs would normally be replaced. The racing miles would indeed be quite harsh, but not near as many cycles as, say, a few thousand miles on the street.

I usually specify "dump truck" parts for my engines to avoid shorter life cycle parts as used in racing.

Just sayin',

Tom
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Old 03-13-2019, 10:13 AM
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If your application is particularly tough on the valve springs, some of the firms like PAC wil offer a nitriding option. The nitrding does not significantly change the spring rate but it does significantly improve fatigue life and operating life. You might want to investigate that as you go about selecting your replacements.


Ed
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Old 03-13-2019, 11:01 AM
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Quote:
Originally Posted by eschaider View Post
If your application is particularly tough on the valve springs, some of the firms like PAC wil offer a nitriding option. The nitrding does not significantly change the spring rate but it does significantly improve fatigue life and operating life. You might want to investigate that as you go about selecting your replacements.


Ed
Agreed. The original engine assembler installed the PAC 1200 series springs. When the failure occurred, I replaced them with the 1500 series.



Added for clarity. Scroll down to page 12.

https://www.racingsprings.com/media/...er-Catalog.pdf

Last edited by HTM101; 03-13-2019 at 11:03 AM..
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Old 03-13-2019, 04:32 PM
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while I agree with pulling the heads off, My thought would first be to boroscope it. You would most likely see shiny marks on the pistons and pressurize the cylinder and listen for air leaks through the intake and the exhaust, that may be enough.
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Old 03-13-2019, 10:45 PM
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Had the same thing happen with 12,000 mi on the motor. After another 500 mi another one went. Pulled the heads and replaced all 16. Since that time I have had the whole motor refreshed (rebuilt).

It's a *****, but $hit happens.
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Old 03-14-2019, 10:49 AM
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If you are goingto leave ANY high performance engine stored for any period of time-------you need to release the pressure on all the rocker arm/ springs---------you can do this at a couple of crank positions where you only need to do half the rockers------

I left race car in garage where dogs and food was------mice took dog food up exhaust header into cylinder with open exhaust valve-----ughhhhhhh, corroded alum race head, top of piston and rusted cylinder wall that will need a sleeve to repair-----
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Old 03-15-2019, 02:07 PM
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Out of curiosity I wrote to PAC about the relative life expectancy of "race" vs "street" valve springs. Here's what I got back:

Quote:
You are correct. Springs designed for very aggressive camshaft profiles generally are high stressed springs resulting in a short lifespan. A spring designed for drag race shouldn’t be used in an endurance application or street use.
Tom
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Old 03-15-2019, 02:21 PM
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Correct Tom. I always go to the circle track/endurance section to select my springs. I check the pressure every winter and I TOSS Them in the garbage every few years and rebuild my lifters. I'll add- if I think they need it. (solid roller)
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Old 03-17-2019, 06:48 AM
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Not long after getting my 427 Center Oiler I began breaking valve springs. I called George Anderson at Gessford Machine to pick his brains and he had me send a whole good spring stack to him including shims and spring cup. He got back to me right away and said they had the wrong spring cup. He offered to order a new set of Comp springs and cups and had them drop shipped to me. No more broken springs. That was 14 years ago. Great guy to deal with. So are Brent Lykins and, before he retired, Keith Craft. They are willing to help out and in return, you can get any parts you need from them. It's worked for me a few times.

Tim
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