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Old 12-13-2011, 08:25 PM
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broken push rods and what I found

I went to fire up my vortec headed 400sbc for the first time after rebuild. Bam bam bam. I wouldn't start. Checked it tonight and see that 4 pushrods are broken all on the same side. These pushrods worked just fine with the old 882 heads. So idk what happened. The rockers are stock vortec ,pistons are stock dish, the pushrods are thicker than the ones from a different 350 so idk what they are for sure some one replaced them i know for sure, and then the springs are the z28 style with the damper spring. Any thought? Do I need to pull anything apart? They all were cracked and bent in all the three same places on the rods. Where it rests in heads, about half way down and the about 2 inches from bottom of rod cracked and bent? Rockers to tight?

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Old 12-14-2011, 12:34 AM
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Quote:
Originally Posted by projectman69
I went to fire up my vortec headed 400sbc for the first time after rebuild. Bam bam bam. I wouldn't start. Checked it tonight and see that 4 pushrods are broken all on the same side. These pushrods worked just fine with the old 882 heads. So idk what happened. The rockers are stock vortec ,pistons are stock dish, the pushrods are thicker than the ones from a different 350 so idk what they are for sure some one replaced them i know for sure, and then the springs are the z28 style with the damper spring. Any thought? Do I need to pull anything apart? They all were cracked and bent in all the three same places on the rods. Where it rests in heads, about half way down and the about 2 inches from bottom of rod cracked and bent? Rockers to tight?
How was the lifter preload set?*
What length are the pushrods?
Was the geometry checked/set, or were the pushrods just installed as-is?
What is the installed height of the springs?
How much lift does the cam have?
Were any cylinder head changes made to handle the lift if the lift is over about 0.460" or so?
Was the cam degreed in?

Before trying to restart the engine, bone up on a few things:

Adjusting hydraulic lifters*

Valve spring installed height- http://www.kmotion.biz/instht.htm
and- http://www.lunatipower.com/Tech/Valv...pringTech.aspx

Valve train geometry- http://www.lunatipower.com/Tech/Valv...nGeometry.aspx
A thread on geometry.
A more recent thread on mid-lift rocker theory HERE.

HERE is a list of valve train points to check.

*This assumes a hydraulic cam.
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Old 12-14-2011, 04:53 AM
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I screwed up on preload i know. I never rotated engine or anything. Just went around and took out slack plus 1/4 turn. I'll check the length. They are the same length as the one out of a 73 350. I presumed the geometry would be fine as it was before. Cam has .480 and the heads are set up to handle .525 between retainer and seal. Cams set with dots matching on the gears. The cam was already installed and was ran with the engine. Installed height is 1.7 inches.
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Old 12-14-2011, 07:08 AM
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Here's a few pictures
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Old 12-14-2011, 07:51 AM
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Checked my valves. All the stems line up and I don't have any sunken ones. Did a leakdown where I pressurized the cylinder and I couldn't here any hissing or sounds lk that. So the valves are seated well. Idk if this will help chase down the problem? Lifters go solid after sitting a year possibly? The original rods are also 7 7/8 inches long.
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Old 12-14-2011, 07:56 AM
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You answered your own question. If you didn't turn over the motor when adjusting the valves, many of them were on the lobe and had close to half-inch of slop once those lifters fell to the cam base circle. Then the pushrods tried to fall out of the lifters or from under the rocker arms!
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Old 12-14-2011, 08:09 AM
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It probably will be a general concensus on this I'm assuming. I was working outside for 7 hours in 20 degree weather with a sweatshirt. I forgot all about setting them the right way.
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Old 12-14-2011, 08:11 AM
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Oh forgot to ask but that would bust em up the way they were?
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Old 12-14-2011, 08:18 AM
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yeah. If they fell out of the seat, got cocked to the side then lifter pressed up. It rested against the top by the head by the valve spring. It used the bottom side where it enters the head as a fulcrum. Something had to give. Repeat this and you get several bends.
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Old 12-14-2011, 08:18 AM
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Quote:
Originally Posted by projectman69
Oh forgot to ask but that would bust em up the way they were?
Sure because then if they stay in the lifter but not the rocker arm when the cam goes to push it back up it may bind on anything that gets in the way.
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Old 12-14-2011, 08:52 AM
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Would it ruin the cam? I'm worried about that part.
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Old 12-14-2011, 10:12 AM
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Quote:
Originally Posted by projectman69
Would it ruin the cam? I'm worried about that part.
The cam and lifters should be OK. If you want to check it anyway, pull the intake so you can get a good look at the lobes through the lifter bores.
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Old 12-14-2011, 10:45 AM
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Quote:
Originally Posted by projectman69
I went to fire up my vortec headed 400sbc for the first time after rebuild. Bam bam bam. I wouldn't start. Checked it tonight and see that 4 pushrods are broken all on the same side. These pushrods worked just fine with the old 882 heads. So idk what happened. The rockers are stock vortec ,pistons are stock dish, the pushrods are thicker than the ones from a different 350 so idk what they are for sure some one replaced them i know for sure, and then the springs are the z28 style with the damper spring. Any thought? Do I need to pull anything apart? They all were cracked and bent in all the three same places on the rods. Where it rests in heads, about half way down and the about 2 inches from bottom of rod cracked and bent? Rockers to tight?
What is the lift at the valve? The production L31 Vortec head is only good for lifts to .45 inch actually many of these heads run into problems at .42 inch. The guides are quite high in these heads to reduce guide and stem wear for emissions purposes. To run lifts higher than .42/.45 the upper guides need to be machined to cut them down. If this isn't done when combined with too much lift the retainer gets jammed into the top of the guide causing a failure of the weakest component in the chain, that almost always is the push rods.

A similar situation can happen with the springs, the L31 does not use a damped spring only a single wind coil. So it is also possible that there is a coil bind situation where at compression of the spring each coil is in hard contact with the adjacent coils, making the spring a solid piece of steel.

There are other possibilities with 2 valve relief flat top pistons being installed backwards so the valves open into the flat surface of the piston and the reliefs are under the squish/quench deck, weird things happen. I think you need to start working backwards from the valve system and check everything
till you find out whats going on, I doubt this is just a bad quality push rod problem. So you gotta find the source of the problem.

I have no idea if the cam, tappets, rockers, retainers, locks, and valves involved survived this. Careful inspection will be needed to find cracks, dents, scratches in surfaces, etc.

Bogie
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Old 12-14-2011, 10:58 AM
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Quote:
Originally Posted by oldbogie
What is the lift at the valve? The production L31 Vortec head is only good for lifts to .45 inch actually many of these heads run into problems at .42 inch. The guides are quite high in these heads to reduce guide and stem wear for emissions purposes. To run lifts higher than .42/.45 the upper guides need to be machined to cut them down. If this isn't done when combined with too much lift the retainer gets jammed into the top of the guide causing a failure of the weakest component in the chain, that almost always is the push rods.

A similar situation can happen with the springs, the L31 does not use a damped spring only a single wind coil. So it is also possible that there is a coil bind situation where at compression of the spring each coil is in hard contact with the adjacent coils, making the spring a solid piece of steel.

There are other possibilities with 2 valve relief flat top pistons being installed backwards so the valves open into the flat surface of the piston and the reliefs are under the squish/quench deck, weird things happen. I think you need to start working backwards from the valve system and check everything
till you find out whats going on, I doubt this is just a bad quality push rod problem. So you gotta find the source of the problem.

I have no idea if the cam, tappets, rockers, retainers, locks, and valves involved survived this. Careful inspection will be needed to find cracks, dents, scratches in surfaces, etc.

Bogie
I screwed up the valve adjustment. The heads were good to .535-.537 lift
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Old 12-22-2011, 06:09 PM
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think i found why my pushrods are breaking

Okay so I have the vortec heads. They have been clearances for .530 lift some a tad more, but anyways I used the z28 springs with the inner damper in. Well I had to turn the springs a certain way so they would sit in the pocket. They fit very snugly onto the boss. Talked to a friend, he's a head machinist, and he said he's never heard of anyone running damper springs with stock vortec bosses and was betting they were hitting the boss.
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