# broken rocker stud



## kjk990 (Sep 1, 2010)

I just had my engine in my 67 GTO rebuilt about three months ago. I have been driving short distances (less than 20 miles) a couple of times a week since then. On saturday I was warming her up in the driveway and she started backfiring through the carb on a pattern. I thought a cylinder was firing out of order, maybe jumping from another spark plug wire. Eventually I figured out that the rocker stud on the #3 cylinder was broken. As you can see in the attached picture the fourth rocker back, the nut is broken off and laying next to it. The third rocker is sideways but the stud does not appear to be broken.

I talked to the machine shop owner. He told me that a batch of studs were over hardened causing them to become brittle. He would replace all of them for free.

A friend said I should check the push rods to see if they were bent. I removed the two from the #3 cylinder (because they were now easily accessible) and rolled them on a flat surface. The one with the sideways rocker was slightly bent. 

What other damage should I look for? If the one rocker stud broke; would that cause the other to have enough movement to turn sideways? Could one of the valves have been not operating for a long time, causing the cylinder to have been dead until the other valve stopped working causing the backfire through the carb? Does the backfiring through the carb cause damage to the carb?

About a month ago I paid a local muscle car shop to tune my engine. They adjusted the MSD ignition, changed the springs in the distributor and set the carb. If the #3 cylinder was not working at that time and now is fixed will my tuning be off?

And finally, I have been dealing with heat issues. would one cylinder not functioning cause additional heat?

Thanks


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## Rukee (Feb 8, 2007)

If that broken stud ended up getting into the spring on the valve next to it, I can see that causing the rocker to come off and bending the pushrod. Replacing the studs should not effect the tune. Dropping a cyl would not cause an overheating issue either. If that cyl was dead durring the tune, they would have not tuned it untill it was repaired.


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## kjk990 (Sep 1, 2010)

So the machine shop guy came to my house to fix the stud. He replaced it along with the push rod from the valve next to it. When he went to replace the rocker arms he said something was wrong. Turns out that the stud that didn't brake had backed out of it's hole about a 1/8 inch allowing the rocker arm to turn sideways hitting the rocker next to it braking it. 

He went ahead and replace it also. He said it may be because of the aggressive cam putting more stress on the studs. 

Has anyone else had this problem? I have an engine from a 70 firebird. The studs are pressed in not screw in. I hope this is just a fluke and that I don't have to replace all of the studs.

Thanks


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## pontiac (Mar 6, 2011)

if your studs are press in, then you might have a problem later on as well. Most applications with aftermarket cams use screw in studs for this reason. much stronger.


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