427 broken valve spring

[RUFdriver]

Broken valve spring means you need to pull the head(s) , high probability of a bent valve. Get a valve job and replace all the springs.
Going forward, the easy thing to do on any motor that will sit for a while is to turn it over now and then. A little more work would be backing off all the rockers to take pressure off the springs.

[era427tp]

After having a 427 for a number of years ,the best advice I got and will pass on is this.Change valve springs every 3 years regardless of use

[Moriarty]

Ugh.. so I finally buttoned everything back up after having taken the head off to inspect the valve. It all looked good, so instead of replacing and lapping a new valve, I decided to roll the dice with the existing one.

I did replace all the springs and seals (and retainers while I was at it). Took it for a test drive yesterday and was noticing slightly louder exhaust note on the passenger side (where the spring broke). Was getting more of a "blat blat blat" than "blub blub blub". I was really hoping for an exhaust leak, since I replaced the exhaust gasket on that side and had taken the pipes off on that side (saw another thread that suggested using some sealer on the four pipes where they connect to the side pipe? I did not do that, and did not see any indication it had been done previously, and am also pretty sure that's not an issue).

Anyway, using a stethoscope I could definitely hear a metal "tap tap tap" coming from the fourth cylinder when I put the probe on the exhaust port while running. Testing again just cycling the engine with the starter, I don't hear any contact, but definitely hear metal sliding against metal.

So.. I'm pretty sure the answer is take the head back off and replace the valve, but thought I'd post here first to see if anyone had anything else I should check first, or while I have the cylinder head back off.

[Robert Beede]

Moriarity: Im not a race engine mechanic, nor do I profess to know lots about the big block drive trains, but after reading all the responses of knowledgeable and well-intended people, I would recommend that you don't get too exotic in your diagnosis, unless the build specs on your engine suggest it should be in a NASCAR, rather than your street cobra. Check for binding. Find out, if you can, exactly what springs you have; often people buy too stiff a spring. Examine the valve stem head to see if it's been mushroomed. Show the spring to someone with expertise in their failure to see if the fractures support the metalurgy inferiority theory. Put a bore scope into the spark plug hole to check out the bent value theory, and look for marks on the piston top. Examine the edge of the oil pan where it bolts to the block for any bulges. Not likely, but a rod cap could have come loose. Drain the oil, and look for any metal. Keep it if found, and show it to a experienced mechanic. The simple answer is that there is too aggressive a spring in your engine. This happens a lot. Just my thoughts. I wish you the best! Bob

[CompClassics]

I am assuming that you have checked your valve train geometry?

[Gaz64]

Looking at your first pic, something doesn't look right with the valve keepers (collets).

One looks bigger than the other, one normal, and one small or broken.

Perhaps the retainer was unstable, and caused the spring fracture.

I find it hard to believe the valve is not bent, your noise on that bank proves it is not seating as well as the others.

Gary

[Robert Beede]

Moriarty: My Friend, after going to the arduous task of removing the head....WHY wouldn't you take it to a master mechanic for disassembly and inspection? From your description of events, you never truly identified THE CAUSE for the spring failure. Now, all of us engaged in this thread have to wait for you to get professional assistance for both you AND your car, to learn what caused the broken spring!😆

[Moriarty]

Looking at your first pic, something doesn't look right with the valve keepers (collets).

Yeah, one half split. Unclear if that happened before and was the cause of the spring failure, or after as a result.

[Gaz64]

The retainer/keeper/valve stem relationship needs to form a lock, so as a test, you should be able to assemble a valve, retainer and keepers together in your hands, and they should lock firmly.

If they don't, the tapers don't match well enough, and then springs break from walking around etc.

Gary

[eschaider]

Moriarity, whether it is a bent valve or you broke another spring, either way the head has to come off. What springs did you use when you did the rebuild?


Ed

[Moriarty]

I used the same parts as were used by the builder when the original owner had the engine was rebuilt in 1998. These: https://www.summitracing.com/parts/cca-928-16 (and yes, they are super stiff, but I assume what the custom cam is spec'd for).

Tonight, I took the valve cover off to check the valve train, and discovered the stud closest to the fourth cylinder had worked itself loose. Turns out, it is completely stripped. Not sure how I was able to torque it to spec when putting things back together - it must have been wedged well enough and then wiggled loose once the engine was running. I want to believe this is cause of the sounds. I've got a Time-Sert ordered to repair the threads, so I'll find out hopefully this weekend. Valve train itself still appears nice and straight.

[Gaz64]

One issue with this shaft mount design is it only has 4 mounting points.
Each pair of valve springs pushes against only 1 stud.

Conversely, some designs have 5 mounting points, bolts or studs.

5 in total gives 2 studs for each pair of valves to push against.

I would timesert or helicoil all the mounting points to run the largest stud possible in the head, even meaning a stepped stud.

The stud should be loctited, and just nipped into the head before the rockers are fitted.

I would also leakdown test all cylinders while the rockers are off to find any leaking valves.

Gary

[eschaider]

Originally Posted by Moriarty

I used the same parts as were used by the builder when the original owner had the engine was rebuilt in 1998. These: https://www.summitracing.com/parts/cca-928-16 (and yes, they are super stiff, but I assume what the custom cam is spec'd for).

Tonight, I took the valve cover off to check the valve train, and discovered the stud closest to the fourth cylinder had worked itself loose. Turns out, it is completely stripped. Not sure how I was able to torque it to spec when putting things back together - it must have been wedged well enough and then wiggled loose once the engine was running. I want to believe this is cause of the sounds. I've got a Time-Sert ordered to repair the threads, so I'll find out hopefully this weekend. Valve train itself still appears nice and straight.

Comp has sourced springs from various firms over the years. One of those firms was PAC. My engine uses a very different spring than yours does however a number of years ago I had problems breaking Comp springs. After I searched around for alternatives I settled on PAC.

As I explained the spring failure and source to the PAC representative he indicated that it sounded like a custom spring they had made for Comp. He also indicated that they did not recommend or offer that specific spring because of the specs the reseller had asked them to build the spring too.

I was steered to a nitrided spring with similar spring rate and a higher intake seat pressure, which I requested because of my higher than ambient manifold pressure. The springs have never failed.

I would be cautious of the spring choice you have made for your engine. PAC has several nitrided alternatives including behive designs that might be worth investigation. Despite the horrific appearance of your many broken spring pieces, you dodged a big bullet — the failure didn't kill your engine. The next one might ...


Ed

[HTM101]

Originally Posted by eschaider

Comp has sourced springs from various firms over the years. One of those firms was PAC. My engine uses a very different spring than yours does however a number of years ago I had problems breaking Comp springs. After I searched around for alternatives I settled on PAC.

As I explained the spring failure and source to the PAC representative he indicated that it sounded like a custom spring they had made for Comp. He also indicated that they did not recommend or offer that specific spring because of the specs the reseller had asked them to build the spring too.

I was steered to a nitrided spring with similar spring rate and a higher intake seat pressure, which I requested because of my higher than ambient manifold pressure. The springs have never failed.

I would be cautious of the spring choice you have made for your engine. PAC has several nitrided alternatives including behive designs that might be worth investigation. Despite the horrific appearance of your many broken spring pieces, you dodged a big bullet — the failure didn't kill your engine. The next one might ...


Ed

Years ago I installed a Comp Cams camshaft, and a matched set of their recommended springs for that cam. About 5,000 miles later, catastrophe set in. The springs of #2 intake broke, the valve dropped, the piston slammed the valve which side-loaded the piston, which cracked the cylinder wall.

The 2nd photo shows the vertical crack in the cylinder wall at the 9 o'clock position that is allowing antifreeze to dribble in.

A very good set of springs costs maybe 5% of what I paid to rebuild that engine.

[eschaider]

Thanks for sharing the painful experience HTM101. That is the price most of us end up paying when a spring goes south. OP, you really did dodge a bullet and most likely will not next time.

Of course it is your engine and your parts and your money sooo, no one is better positioned to determine what you want to do with all those things than you ...


Ed


p.s. Comp is sort of good with their off the shelf cams. Not so much with springs.