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Old 06-22-2008, 11:32 PM   #1
Aggravated4life
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Default What Causes a Pushrod/Rocker Arm To Become Loose?

My neighbor built a 460 chevy big block and has it running.I was going to take pics and a video,but lo and behold one of the rocker arms went sideways and the pushrod got damaged,rubbing up against the guide.

He replaced the pushrod and readjusted the valve lash with motor running and etc.That same rocker arm seems to want to come loose or move sideways again.

Hes the mechanic so Im sure he will figure it out,but I was curious as well to what can cause this to happen on just one area?The others are fine and working great.

The heads,engine had full machine work done by a shop he uses,yet he put the entire engine components back together himself.Hes built many motors at home and never had this happened before either.

Im very curious to what can cause this problem on a big block or any chevy engine for that matter.He has a comp cam,springs, rocker arms and/or the matched comp valve train set for his particular build.

Any ideas or links is appreciated.Im just very curious to know what might be a common cause.

Thanks!
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Old 06-23-2008, 01:03 AM   #2
steves65korvette
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Boss where rocker arm stud is installed may be busted,,,letting stud pull out. Rocker arm boss should be milled and screw in studs installed for a HP application. If running hydraulic lifters, it may be bad and leaking down. Although I think it would have to leak off really quick to allow the rocker to jump off like that. Just a couple of possibilities. Steve
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Old 06-23-2008, 01:12 AM   #3
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i followed that first thread and requested a vid.. i hope he gets it worked out
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Old 06-23-2008, 01:16 AM   #4
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Quote:
Originally Posted by steves65korvette View Post
Boss where rocker arm stud is installed may be busted,,,letting stud pull out. Rocker arm boss should be milled and screw in studs installed for a HP application. If running hydraulic lifters, it may be bad and leaking down. Although I think it would have to leak off really quick to allow the rocker to jump off like that. Just a couple of possibilities. Steve
Thanks Steve...
From what I can gather,he removed the stud and checked it for damage.Did not see any damage inside the boss itself.
( may need another closer look)

Didnt appear to be any.Rocker arm itself was not damaged.Just the pushrod got damaged by rubbing the guide plate.

He put it back together and installed a new pushrod and did the adjustments again.

The rocker arm doesnt just slip off but if you tap it with a socket,while the engine is running,it will go off sideways.It originally slipped off on its own.

None of the other studs or rocker arms or push rods do this.I wonder if there ca be a crack inside the boss that one cant see by simply looking at it.The stud does seat and torque to specs.THis is gonna be interesting.

Thanks again.

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Old 06-23-2008, 01:21 AM   #5
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Quote:
Originally Posted by cdg2000c5 View Post
i followed that first thread and requested a vid.. i hope he gets it worked out
Me too...I wanted to take pics and a vid and this happened.Hope its nothing too serious.He was a bit pissed off today when trying to diagnose wtf was going on but is gonna have to put it on hold since he has to work all week,but hope he gets it fixed soon.If theres a problem in the head,lifter,or the spring seat that would suck,but im not sure what will come of it.

Will keep ya all posted...im excited for him yet same time undy his frustration right now.Just never seen it happened before.
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Old 06-23-2008, 02:50 AM   #6
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Some rocker arm studs are pressed into the head, not screwed in. It may just be backing out.

There are procedures to fix this like pinning the stud through the boss.

Does he have poly locks or lockable nuts on the studs?

If not, just replacing the nut may solve the problem.

OR

Do like we did back in the old days when money was tight, we just whacked the nut with a hammer to slightly warp the hole making for a tight fit that didnít back off.
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Old 06-23-2008, 03:25 AM   #7
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Uuuuuuhhhhhhhhhhhhhhhh. Vibration?

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Old 06-23-2008, 03:49 AM   #8
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Quote:
The rocker arm doesnt just slip off but if you tap it with a socket,while the engine is running,it will go off sideways.It originally slipped off on its own.
Try swapping that rocker arm & stud with a set from another location to see if the problem goes with the set of stays with that location.

If the problem moves with the pair, then move just the rocker arm.
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Old 06-26-2008, 12:19 AM   #9
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Thanks for all the suggestions...I spoke with my neighbor and he spoke with the engine machinist that did the machine work.He was told to use roller rocker arms,or roller tips and hardened pushrods,since the cam he used can cause this problem with the stuff hes running now.

Hes going to try this route and see if the engine machinist is right...so far there are no other mechanical problems found.

I do like the idea of switching and see if it moves.I'll suggest that to him as well as advice off here.

But as I said,they believe the problem is with the new cam and springs,and the stamped rocker arms- pushrods need to be replaced.
We shall see this week how it goes.
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Old 06-26-2008, 12:32 AM   #10
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I am going to go out on a limb here, but I have been up this tree more than a few times with a BBC.
If he is running a big cam with a lot of spring pressure and does not use the proper break-in and do a proper warm up EVERY time he starts the motor he may have done what I have done more times than I want to remember.
If the stud is not coming out and the nut is not coming loose that only leaves a lobe going away.
BTDT.
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Old 06-26-2008, 12:36 AM   #11
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Quote:
Originally Posted by blown87 View Post
I am going to go out on a limb here, but I have been up this tree more than a few times with a BBC.
If he is running a big cam with a lot of spring pressure and does not use the proper break-in and do a proper warm up EVERY time he starts the motor he may have done what I have done more times than I want to remember.
If the stud is not coming out and the nut is not coming loose that only leaves a lobe going away.
BTDT.
That sounds like good advice...Im going to pass that along.Yeah they are saying they believe its the bigger cam and spring pressure along with stock rocker arms and non hardened push rods that may be the culprit,but more info like yours always helps.

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Old 06-26-2008, 12:36 AM
 
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