Author Topic: 186 heads - rocker arm studs  (Read 3160 times)

Stingr69

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Re: 186 heads - rocker arm studs
« Reply #15 on: November 16, 2019, 10:57:23 PM »
Keep in mind...GM found the stock pressed in studs to be a weak point and redesigned the SHP heads to use the hex style screw-in studs and guide plates on even the lowly L-82 engines.  They did not add them just because they look sexy with the valve covers off.  GM required them on every HP engine from 1970 all the way thru the 1980's.    They also redesigned the inside of the finned aluminum valve covers at the same time to add the drippers to improve reliability. 

69Z28-RS

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Re: 186 heads - rocker arm studs
« Reply #16 on: November 17, 2019, 09:18:51 PM »
I suspect the problem (if it was a real problem) came about due to solid lifter,  higher revving engines, especially when higher pressure valve springs are used with higher lift cams.  Chevy used the press in studs for at least 15-20 yrs prior to 1970, including the SHP corvette engines of the mid sixties, and first gen Z28's.   I've never had one pull out, but the engine in my '69 Z28 had one that had pulled out prior to my obtaining the car, but it was also owned by a young teenage girl for a few years and her and her teenage bf raced it quite a bit... :)    You can just about guarantee that it was over revved when the stud let loose..    and Yes, you CAN over rev a 302... (You know you over revved it when something breaks!   ... and that's why so few early Z28's had their original engines more than a couple of years...
Gary W / 09C 69Z28-RS, 72 B 720 cowl console rosewood tint
69 Corvette convertible, silver/black 350 hp,
60 Corvette white/red, 72 Corvette coupe, '70 Mach I 
90 ZR1 red/red #246, 90 ZR1 white/gray #2466
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Stingr69

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Re: 186 heads - rocker arm studs
« Reply #17 on: November 18, 2019, 06:09:33 PM »
Why risk it?  There are other people having bad experience with this hexless rocker stud mod. 

https://chevroletforum.com/forum/engine-building-overhauling-43/cylinder-head-cracked-49940/
Also, If you need to fix an alignment issue caused by the new screw in stud being out of alignment with the valve stem you are "screwed" literally.  :D   

69Z28-RS

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Re: 186 heads - rocker arm studs
« Reply #18 on: November 18, 2019, 11:23:53 PM »
The example you cited appears to be a situation caused by the owner/installer - perhaps improperly drilled prior to the tapping of the threads.  There's also something 'sticking up' around the stud... was it not tapped deeply enough and he screwed the stud in too far stripping out the threads and cracking the boss?   Apparently he rebuilt the engine himself and the problem occured before it ever ran.   This sounds to be like an 'amateur' attempting to build his own engine without having the proper knowledge or experience...

I've never heard of the screw in studs having an issue personally...
Gary W / 09C 69Z28-RS, 72 B 720 cowl console rosewood tint
69 Corvette convertible, silver/black 350 hp,
60 Corvette white/red, 72 Corvette coupe, '70 Mach I 
90 ZR1 red/red #246, 90 ZR1 white/gray #2466
72 El Camino, '55-'56-'57 Nomads, '55-'57 B/A Sedan

Stingr69

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Re: 186 heads - rocker arm studs
« Reply #19 on: November 19, 2019, 07:11:00 PM »
The example you cited appears to be a situation caused by the owner/installer - perhaps improperly drilled prior to the tapping of the threads.  There's also something 'sticking up' around the stud... was it not tapped deeply enough and he screwed the stud in too far stripping out the threads and cracking the boss?   Apparently he rebuilt the engine himself and the problem occured before it ever ran.   This sounds to be like an 'amateur' attempting to build his own engine without having the proper knowledge or experience...

I've never heard of the screw in studs having an issue personally...


The stud needs something to tighten against or it will never torque to spec.  Rocker stud holes are not blind as they go into the water jacket. The raised area on the side of the stud will contact the top of the boss as a stop but the torque spec required to seat the threads is enough to crack the top of the boss. 

(Scroll down to the bottom)

http://forum.grumpysperformance.com/viewtopic.php?f=52&t=2746

Kelley W King

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Re: 186 heads - rocker arm studs
« Reply #20 on: November 19, 2019, 09:36:18 PM »
I have used hex less screw studs and had no issues but had the machine shop do it. And actually the only press in stud I have had pull out was with hydraulic lifters. A little wild on the cam but hydro lifters.
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z28z11

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Re: 186 heads - rocker arm studs
« Reply #21 on: November 20, 2019, 03:26:48 AM »
I forgot to add this earlier - GM used to sell oversized studs (.002", if I remember correctly) as a service part for those unfortunate enough to pull a stud out, or have one come loose. I've never had one pull, even with running an Erson hydraulic with pretty stout Erson springs, no give up ever. If you've ever replaced a damaged or broken stud (I have on a customer's small block a long time back), they are really tough to break loose. Pinning used to be common, but I never thought it was needed on a street engine - 

Regards,
Steve
1968 Z28 M21/U17 BRG/W
1969 Z28 X77/M20/VE3 LeMans/W
1969 L78 X66/N66 Cortez/BVT
1969 Z11 L48/M35/C60/C06

70z28lt1

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Re: 186 heads - rocker arm studs
« Reply #22 on: November 20, 2019, 01:19:07 PM »
Just like everything there were tolerances on the parts.  A few tenths small (still in spec) on the shank of the stud mated with a hole that is a few tenths on the high side and you have a marginal fit that may live forever on a low lift, low RPM engine but on a 302 or similar it would pull out eventually.  That's why as posted earlier they went to screw in studs on SHP applications.  There must have been enough warranty claims to make it worthwhile.  The General didn't do things like this without good reason.
My advice would be if you didn't care about appearance, machine them for screw in studs and guideplates.  If you cared a little about appearance pin them and if you are really hard core then pull all of them and select fit studs to bores for the maximum press fit along with a dab of red locktite.

69Z28-RS

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Re: 186 heads - rocker arm studs
« Reply #23 on: November 20, 2019, 02:19:22 PM »
It's good that you have a '70 with GM screw in studs....   :)
Gary W / 09C 69Z28-RS, 72 B 720 cowl console rosewood tint
69 Corvette convertible, silver/black 350 hp,
60 Corvette white/red, 72 Corvette coupe, '70 Mach I 
90 ZR1 red/red #246, 90 ZR1 white/gray #2466
72 El Camino, '55-'56-'57 Nomads, '55-'57 B/A Sedan

z28z11

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Re: 186 heads - rocker arm studs
« Reply #24 on: November 22, 2019, 02:36:19 AM »
I said .002", obviously I meant .003" (lol). These two are about 49 years old, used to have blue paint on the bottom of the studs denoting the oversize shanks. Trick to install them was to freeze them, heat the boss with a torch, drive into place using a lock nut to protect the threads. You had to be quick - once they came to temp, they were in for a good while. Danged tough material, too - if you ever adjusted valves frequently, you knew that the lock nuts would wear a lot faster than the stud threads. Using two piece locking retainers was better over time than taking a chance of lock nuts backing off.

My heads are still originals, never hot tanked or disturbed (other than Erson springs, PC seals). I had the occasion to change a couple of damaged studs out on a '68 291 head on my Bel Air around '70, had these left over. Amazing how things can accumulate -
1968 Z28 M21/U17 BRG/W
1969 Z28 X77/M20/VE3 LeMans/W
1969 L78 X66/N66 Cortez/BVT
1969 Z11 L48/M35/C60/C06

rszmjt

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Re: 186 heads - rocker arm studs
« Reply #25 on: November 27, 2019, 01:35:10 AM »
Iíve used the Mr Gasket 1076 screw in studs with the small shoulder with great success in the past, we use a small end mill and counterbore the head stud hole after tapping so the small shoulder is encapsulated and has a positive stop, being careful not to overtorque and also use copious amounts or red loctite. If you donít counterbore the head sometimes the rocker rubs on the small shoulder. My own Z has had these studs in for 35 yrs+ with no problems. Of course you could also use 70 style screw in studs and guide plates but I kinda like the stock type appearance.