What could have caused this broken valve spring?
Thread Starter
On The Tree
Joined: Dec 2012
Posts: 177
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From: Troy, MO
What could have caused this broken valve spring? Spring on valve train broke and the valve cam up through the cylinder head. New build with less than 200 miles. Stock pushrods, 317 Heads with PBM3250 valve springs. .595 lift cam.
Staging Lane
Joined: Sep 2008
Posts: 78
Likes: 0
From: West Chester, PA
If they were all okay then maybe you got a bad bach of springs. Check those push rods too! I can't tell if its from the angle but the one looks a little bent.
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there is also more to matching springs to a cam than pure lift capacity.
The picture you paint for us with stock pushrods, and only giving us lift with no other cam data.
Makes it seem a whole lot like you got in over your head and picked mismatching components and then likely assembled them less than well.
The picture you paint for us with stock pushrods, and only giving us lift with no other cam data.
Makes it seem a whole lot like you got in over your head and picked mismatching components and then likely assembled them less than well.
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Thread Starter
On The Tree
Joined: Dec 2012
Posts: 177
Likes: 0
From: Troy, MO
there is also more to matching springs to a cam than pure lift capacity.
The picture you paint for us with stock pushrods, and only giving us lift with no other cam data.
Makes it seem a whole lot like you got in over your head and picked mismatching components and then likely assembled them less than well.
The picture you paint for us with stock pushrods, and only giving us lift with no other cam data.
Makes it seem a whole lot like you got in over your head and picked mismatching components and then likely assembled them less than well.
I didn't pick the components but thought I had a reliable engine builder that knew what he was doing. Told him what I wanted the engine to do so he picked the cam and pistons and sent me to the machine shop that bored the block and reworked the heads. The communication was supposed to be the engine builder talking with the machines shop, at that point I was only the delivery driver.
I think the machine shop should have known what springs were required as he had the cam spec sheet. The engine assembler should have known or measured for correct push rod length. I get to pick up the pieces and pay for their mistakes. Now am looking for guidance because I already paid them both fairly and don't need to pay twice for their mistakes. The engine assembler immediately blamed the machine shop for incorrect springs. I am going to machine shop first thing in the morning. I need to replace a head and get the correct springs and push rods. The ends of the bent push rod didn't appear to be flat or scared like it failed first. Looks like spring broke then all hell broke loose.
I will learn and do it myself.
Pulled the head this afternoon. Found a little ding on the top of the piston a small nick in the cylinder wall.
Last edited by donnie_19; Jun 2, 2013 at 08:10 PM.
Thread Starter
On The Tree
Joined: Dec 2012
Posts: 177
Likes: 0
From: Troy, MO
Here is the cam data
Lift intake@cam 0.35 at valve 0.595 Rocker arm ration 1.7
exhaust 0.35 at valve 0.959
Cam Timing Advertised duration 296 degree
Cam timing@.050
Opens intake 11 degrees Closes 47 degrees ABDC Max Lift 108 ATDC
Duration 238 and 242
exhaust 57 degrees 5 degrees ATDC 116 BTDC
Lift intake@cam 0.35 at valve 0.595 Rocker arm ration 1.7
exhaust 0.35 at valve 0.959
Cam Timing Advertised duration 296 degree
Cam timing@.050
Opens intake 11 degrees Closes 47 degrees ABDC Max Lift 108 ATDC
Duration 238 and 242
exhaust 57 degrees 5 degrees ATDC 116 BTDC
Staging Lane
Joined: Sep 2008
Posts: 78
Likes: 0
From: West Chester, PA
I don't know what shop set up your heads, but they set them up to fail. Max lift on the cam was .595 at the vale, you spring could only handle .600. You need at least .625 or better .650 to prevent coil bind.
Stacked tolerances happened here. Which made it very easy for that spring to brake. Were the base to the retainers measured? Was any of them shimmed? To make for equal pressure?
I'm not trying to throw anyone under the bus, I know you want an answer to what happen. And so it won't happen again.
Bottom line, not enough spring clearance. You left yourself with .005! That's five thousandths of an inch, thats like a human hair, Im not kidding you left your self no room, a human hair is .004! Heat from the engine will make everything including pushing rods and expand, and depending on how hot it could have gotten and at what rpm it was when it into bind, bent the push rod and the valve prob. Smacked the piston.
I've got some good photos of the exact same thing that happened to my buddies TA. not enough spring height! If you want to check it out its over at If you want to check it out its over at https://ls1tech.com/forums/showthrea...1568771&page=4
I see 2 major issues. The spring pressures are extremely low and looks like the locks do not fit the retainer. If I were to guess I would say your retainer/lock failed and dropped the valve right through the head.
Please post pics of the locks and retainer of the failed valve and take more pictures of the assembeled valves.
Thanks,
Matt
Please post pics of the locks and retainer of the failed valve and take more pictures of the assembeled valves.
Thanks,
Matt
I don't know what shop set up your heads, but they set them up to fail. Max lift on the cam was .595 at the vale, you spring could only handle .600. You need at least .625 or better .650 to prevent coil bind.
Bottom line, not enough spring clearance. You left yourself with .005! That's five thousandths of an inch, thats like a human hair, Im not kidding you left your self no room, a human hair is .004! Heat from the engine will make everything including pushing rods and expand, and depending on how hot it could have gotten and at what rpm it was when it into bind, bent the push rod and the valve prob. Smacked the piston.
Bottom line, not enough spring clearance. You left yourself with .005! That's five thousandths of an inch, thats like a human hair, Im not kidding you left your self no room, a human hair is .004! Heat from the engine will make everything including pushing rods and expand, and depending on how hot it could have gotten and at what rpm it was when it into bind, bent the push rod and the valve prob. Smacked the piston.
Thread Starter
On The Tree
Joined: Dec 2012
Posts: 177
Likes: 0
From: Troy, MO
Just returned from Machine shop and as I figured he said the engine assembler specified the springs. He also thought that should not have failed but will try and work with me on repairs. The machine shop will call engine builder as they have worked together on several builds. I need to pull engine and get the number 3 cylinder honed to take care of the nick as well as check the rod and bearings. Here is a couple of pics of the valve springs assembled. Ordered a replacement the cylinder head.
Staging Lane
Joined: Sep 2008
Posts: 78
Likes: 0
From: West Chester, PA
0.100" clearance from coil bind is a ton of room. Most spring manufaturers rate there springs for max lift with a 0.050"-0.060" clearance.