I have a 1966 L79 which has a pulled rocker stud on the #8 intake valve. The stud is setting approximately 1/8 of an inch higher than the rest of the studs. What are my options to fix this?
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Re: Pulled rocker stud on L79
Scott:
The first question to ask is "why"? Are the heads stock? If not, then what was changed?
The easiest fix, provided that the stud boss is still intact, is to have it, and the new stud drilled and pinned. If any performance modifications were done, then the prudent alternative would be to remove both heads, and have the bosses threaded to accept threaded rocker studs.
Joe -
Re: Pulled rocker stud on L79
I had a rather agressive aftermarket cam in it. I am in the process of installing the correct L79 cam and noticed the stud is setting 1/8 higher during valve adjustment.Comment
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Re: Pulled rocker stud on L79
Scott,
I agree with Joe on the screw in studs. If the engine is apart and the heads are off, this would be a first choice. GM still sells the studs and guide plates if you choose to go that route. If you don't want to remove the heads, it would be possible, and logical, to install a new press in stud. Since you are installing the original 151 cam, the press in studs are sufficient as long as you never take the engine up to valve float RPM. This is when the trouble starts.
If you decide to install a new stud, a word of caution is in order. The original size stud has never been available in service. The only studs that are available are .003 and .013 oversize and the original hole MUST be reamed to the new size or a crack is almost sure to occur in the stud boss. I've seen it happen many times.
MichaelComment
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Re: Pulled rocker stud on L79
The heads are still on the engine. However, the intake is off so I would just have to pull the exhaust maniford in order to pull the head. Since I am going back to the factory cam can I drive the stud back in? If I go with screw in studs do I need the guide plate?
Thanks,
ScottComment
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Re: Pulled rocker stud on L79
Driving the stud back to it's original location is a temporary fix, at best. It would certainly get a car home in an emergency but once they move, it would never be durable again, especially at high RPM. The ream and .003 replacement stud is really the only fix that can be performed with the heads still in place. I know many will disagree but I don't think it's possible to completely eliminate the metal chips from threading, from falling into the engine and cooling system. (most studs go into water)
You can try resetting the stud and see what happens but I would probably at least order a new .003 stud and reamer, just so you have it handy, or plan on screw in's in the near future.Comment
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Re: Pulled rocker stud on L79
Michael:
Thanks for the help. The over size stud seems like to way to go. What size does the hole need to be reamed to in order to be correct for the oversize stud? Does anyone have a PN for the stud?
Thanks,
ScottComment
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Re: Pulled rocker stud on L79
If you are returning to the stock (hydraulic) cam and the stock valve springs, I would first try just pounding the stud back into place. The stock components, especially on a hydraulic engine don't really stress the stud that much.. Just keep the rpm under valve float.Bill Clupper #618Comment
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Re: Pulled rocker stud on L79
Scott,
I think I agree with Bill. If the car will see only mild service, it's probably worth a try on the original stud. If you drive the stud back in and you feel a lot of resistance, it may last forever. If, on the other hand, you notice that it slips back to correct height with little resistance, you have no choice but to replace it. I don't know how to describe the effort required to reinstall but if it goes in like a finish nail in pine, you're looking at replacing it. If it offers the same resistance as a 16 going into oak, you will likely be ok. (now THAT'S a pretty bizarre description!)
The part numbers are as follows, in group 0.429. The .003 OS is a 3814692 and the .013 OS is 3815892. These numbers are from an old 74 printing so there could be a number change. Someone with a current book may correct these numbers.
I can't find the size of the ream but the Kent Moore numbers are J-5715 for the .003 and J-6036 for the .013. Hopefully someone has the sizes handy.
MichaelComment
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That's a pretty good description to drive a stud
in Mike.
I believe I'd drive it back and and maybe go ahead and drill the boss and pin it if it came loose again. My experience, if it goes back in good and solid, it will stay unless you do something extreme. And, yes ream the boss if you put in a .003 oversize stud. It WILL most likely crack the boss if you don't. I've been there.Comment
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Re: Pulled rocker stud on L79
Scott - I actually installed a set of ARP screw in studs on a friend's 66 this spring. We did use specal tools to pull the studs, spot face the bosses, and thread the stud bosses using lots of vacuum power etc to control chips. It is possible, but not nearly as easy as with the heads off. You can also get threaded studs without the hex boss that can just be threaded in the original boss. The pin idea is fine too......we just wanted the added strength of the ARP professional grade studs threaded in....CraigComment
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Re: Pulled rocker stud on L79
I put jammed two nuts together on the stud and drove it back down using a ball peen. I would say that it went in like a number 16 going into oak. So, I think I am going to finish assembling the engine and keep any eye on that stud. If it pulls up again I will remove both heads and have screw in studs installed.
Thanks to all who responded,
ScottComment
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with the intake off you can drill and tap the
stud boss for the instalation of a #10-32 set screw. you do not need to drill thru the stud just deep enought for the #10-32 set screw to grip the stud. i have done this different times with great success when a stud pulled. the over size reamer is not cheap and to do just one stud it is kind of a waste of money. if you want to change the stud get the .003 over size one,mic the orignal stud OD and have the .003 oversize stud turned down in a lathe using a carbide tool to .001 over the orignal OD. i have done this if the orignal stud was damaged and could not be reused. put the stud in dry ice for several hours and it will go in without cracking the stud boss.Comment
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Re: with the intake off you can drill and tap the
Clem:
Thanks for the suggestions. If it pulls up again, I will get the .003 stud and turnd it in the lathe.
Thanks,
ScottComment
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Re: with the intake off you can drill and tap the
On your stud you just drove back down, clean it with brake cleaner and let dry. Then take a paint stick and dab some white paint where it meets the boss. Not thick, just lightly. This will show a gap easily if it begins to pull up.Comment
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