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SBC 400 - one rocker nut keeps loosening ?

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Old 02-20-2011, 11:29 AM   #1
my75baby
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Default SBC 400 - one rocker nut keeps loosening ?

Hello all I need a motorhead to answer this one, I recently replaced the cam, rocker arms, nuts and lifters on my SB 400. However one rocker arm nut keeps loosening up and I do not know why. I tighten it (adjusting the valve properly) and then drive the car for a while only to find it loosens up and starts clacking again. Anyone ever experience this before? I figure when the hydraulic lifter is properly loaded it would prevent the nut from loosening, but it keeps doing it.. any ideas?
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Old 02-20-2011, 11:41 AM   #2
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do you have pressed in studs? if you do a high lift cam will pull them up. was a common problem years ago. otherwise, poly locks should help
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Old 02-20-2011, 12:04 PM   #3
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Even if you have threaded rocker studs, check the torque and make sure that it isn't coming loose. I had a chronic problem with my stroker. All it took was 8 globs of Loctite red and the problem went away.
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Old 02-20-2011, 12:43 PM   #4
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LOL.. thanks guys, I was thinking about threadlocker on this particular nut, just didnt think you were supposed to use that on rocker studs.. but it MUST stop doing this. I was almost going to double nut it
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Old 02-20-2011, 12:46 PM   #5
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Been awhile, but last build I did used longer rocker arm nut's with allen type jamb screw's on top. Not really sure where I got these, but running a high lift cam, and nothing's moved.
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Old 02-20-2011, 12:57 PM   #6
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Quote:
Originally Posted by my75baby View Post
Hello all I need a motorhead to answer this one, I recently replaced the cam, rocker arms, nuts and lifters on my SB 400. However one rocker arm nut keeps loosening up and I do not know why. I tighten it (adjusting the valve properly) and then drive the car for a while only to find it loosens up and starts clacking again. Anyone ever experience this before? I figure when the hydraulic lifter is properly loaded it would prevent the nut from loosening, but it keeps doing it.. any ideas?
A couple things here, but are you sure the nut is backing up? As said make sure the stud is not getting loose or pulling out. Does the nut feel loose when you re-adjust? And the worst one check and be sure the rocker is moving the same amount as the others, (lobe going flat)
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Old 02-20-2011, 02:32 PM   #7
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Quote:
Originally Posted by Manuel Azevedo View Post
A couple things here, but are you sure the nut is backing up? As said make sure the stud is not getting loose or pulling out. Does the nut feel loose when you re-adjust? And the worst one check and be sure the rocker is moving the same amount as the others, (lobe going flat)
there ya go!......
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Old 02-20-2011, 02:49 PM   #8
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Quote:
Originally Posted by Manuel Azevedo View Post
A couple things here, but are you sure the nut is backing up? As said make sure the stud is not getting loose or pulling out. Does the nut feel loose when you re-adjust? And the worst one check and be sure the rocker is moving the same amount as the others, (lobe going flat)
There is may be one thing a 6 sec man not might be aware of. Cheap CHinese push-rods being manufactured under legit US companies. Do these push-rods have the little ***** on the end of them ?
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Old 02-20-2011, 03:12 PM   #9
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Quote:
Originally Posted by Manuel Azevedo View Post
A couple things here, but are you sure the nut is backing up? As said make sure the stud is not getting loose or pulling out. Does the nut feel loose when you re-adjust? And the worst one check and be sure the rocker is moving the same amount as the others, (lobe going flat)
I'd mark the nut and the stud, then check to see if the marks are still aligned when it starts clacking again. If they still match up you know the problem is one of the other things mentioned.
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Old 02-20-2011, 07:36 PM   #10
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All very good suggestions guys, thank you. As for the cam, it is brand new so it has not had time to wear a lobe down. It is either loosening or, as stated, I am pulling the stud out of the head. If that is the case, is there a way to put a pressed stud back in the head without taking the head off?
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Old 02-20-2011, 08:09 PM   #11
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Originally Posted by my75baby View Post
All very good suggestions guys, thank you. As for the cam, it is brand new so it has not had time to wear a lobe down. It is either loosening or, as stated, I am pulling the stud out of the head. If that is the case, is there a way to put a pressed stud back in the head without taking the head off?

Well it may not be a lobe thats why to check everything. But a new cam is the most vulnerable to going flat.
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Old 02-20-2011, 08:16 PM   #12
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Well this is what happened to one of our engines. First off, 383, Vortec heads, CJ 7. Son floated valves at 7k+ rpm while in a snow bank last winter. I notice a rocker noise. I tightened the rocker, noise came back after about 3 minutes of running around 3k rpm. I measured the stud height, sure enough #2 exhaust stud pulled. Here is a bubba fix, temp to perminate. I just removed the rocker assy, and reinstalled the nut flush with the stud. I then smacked the stud with ball peen hammer. lol I made sure the stud was level with all the others using a straight edge. At this time I reinstalled the rocker assy and tightened as needed. That was over a year ago and no problems at all. I figured it would pull back out but has not. Some my flame me, but $0 cost and it worked. Heck I did not even have to replace the cover gasket due to it being the new rubber type. Try it, worst case it does not work and you have to have a new stud installed. Al
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Old 02-20-2011, 08:22 PM   #13
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Very true Manuel, however this is a totally stock cam, used molykote on lobes and lifters and break in oil, and when I tighten it down its fine and car runs great. I am doing the opposite of what most guys do on here, I am building more of a driver than a racer. Have a 600cfm Edelbrock with stock cam, I want no lub at all, just smooth. Stock T10 with stock clutch. The car runs beautiful with no shaking or vibration and is a blast to drive. I will be quieting down the exhaust as well. I know its blasphemy... but car is still pretty quick with the 400 in it. If I want to go fast, I will just drive my Jag, (that one has the supercharged motor and is crap your pants fast,, LOL)
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Old 02-20-2011, 08:26 PM   #14
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this is why all of the high performance Chevy's had screw in studs
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Old 02-20-2011, 09:28 PM   #15
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Well if the stud worked its way out I will just tap it back in like Al said, does anyone think double nutting it will work if its not the stud and just a nut loosening?
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Old 02-20-2011, 09:50 PM   #16
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Quote:
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Well if the stud worked its way out I will just tap it back in like Al said, does anyone think double nutting it will work if its not the stud and just a nut loosening?
Double nutting will work. But if your nut is actually backing off, its just worn out. You can buy replacement rocker nuts fairly cheap.
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Old 02-20-2011, 10:03 PM   #17
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My own experience:
rebuilt a 350 with a new Edelbrock cam, heads, gaskets.
Set the hydraulic lash 1/2 turn past....cranked engine up over 2200 for 30 minutes.

It ran crappy. Pulled the valve covers.......one rocker was loose. I tightened and repeat.
Same thing, same rocker loose. Tightened again.......same result.

End of the story.........one lobe on the new cam was wiped down immediately at start-up. Edelbrock agreed to ship another cam free of charge(they rule).
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Old 02-20-2011, 10:45 PM   #18
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Thanks Driveshaft, these are new nuts though.. Hey snoopy this cam is not an Edelbrock, and it better not be wiped.. I think its just loosening up it really does run great.. even when loose.. just clacks...
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Old 02-20-2011, 10:53 PM   #19
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Have you put a straight edge across the studs to see if it has pulled? I am hoping it has not. mike...
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Old 02-20-2011, 11:16 PM   #20
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I will try that tomorrow.. not much I can do if it is.. just try to tap it back in square with a ball peen.. if not I guess I have to pull the head..
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