Breaking rocker arm studs

JohnnyD

New Member
Aug 6, 2022
9
yes the heads are new and new to me and limited to advanced knowledge.. the original were both cracked and i purchased 2 new ones from the auto machined shop that was doing all my work. I agree with you the geometry is off. Since day one when i started having to buy parts for the engine i was giving wrong parts . I have the MPFI spider fuel injected engine with the plastic upper manifold . The new heads i was told to be heavier around where the valve seats since it was a problem with heads cracking on the originals . the push rods lengths is my present problem. GM 10241740 are 7.122 and every set i have ordered have been 7.195 i even recieved 7.203 every source says the 7.195 will work . Is a .073 difference in length gonna cause a problem ? the self guided rocker arms are 1.50 to 1 . the heads have to be torqued using a degree dial. the cam is new according to Chevrolet Dealer mechanic is correct one but like i said earlier trouble recieving wrong parts so who knows. ok so my next step is to use a push rock gauge for correct length. thanks ob355 , tom3 , biker , twisted metal for all good responces im gonna figure it out im not discouraged. i started this going on a year now with the pandemic , shipping hard to get parts and all.
 

Bills69

Veteran Member
May 28, 2018
375
I had an issue with new replacement heads after chasing everything in question
Head manufacture says studs were of good quality and sent replacements still the same problem
I changed all studs to ARP brand and not a problem since
 

ob355

Member
Mar 4, 2022
95
I rather the studs break then putting a hole in piston. he needs to check piston to valve clearance. find out what parts are not working with what he has.
 

biker

Veteran Member
Gold Member
Dec 7, 2014
5,277
Canada
The other thing none of us has mentioned is valve guide boss clearance. Stock vortec heads can have clearance issues with even moderate increases in cam lift. I dont know what your cam lift is, but having a rocker tip bottoming hard against the retainer could possibly snap a stud.
 

1320feet

Veteran Member
Oct 23, 2019
517
Calgary, Alberta.
Is the slot in the rocker long enough? Is the edge marked in red hitting the stud? A longer push rod will decrease this clearance.

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Rascal

Veteran Member
Apr 18, 2002
300
Severna Park, MD
My .02,
I would stop and disassemble the top of the engine; intake, heads and camshaft, then fully inspect for any damage.
If damage address how bad and repair as required.
If NO damage reinstall cam at dot to dot on crank/cam gears and one head with head gasket and 3-4 bolts just enough to tighten head AND put putty/clay on piston #1 intake valve relief about a dime size ball is sufficient.
Rotate enigine; I use the $20 tool that attaches to harmonic balancer and avoid using crank snout bolt. This avoids possibly and often likely stripping crank snout bolt. After FULL rotation pull head off and inspect piston to valve clearance. I use an unwound paper clip and sharpie. Poke the paper clip in clay/putty in the intake valve indentation on piston and mark paperclip. Then measure preferably with a caliper. The Intake valve should have at minimum 1/10”. Prefer 1/8” or greater on stock engine.
As long as your piston to valve clearance is good. I would then go thru the FULL cam degree process with a dial gauge AND an adjustable pushrod. This WILL identify the pushrod length required, valve train geometry (correct or incorrect), verify cam lift & duration, and required rocker arm ratio. Most importantly it will identify most if not all valve train geometry issues. I’m sure you’re aware but I’ll state anyway;
Ideally rocker arm tip should start slightly off center of the valve stem and move to the center of the valve stem at full cam lobe lift. Optimally at this time you can also determine if cam should be advanced or retarded based on cam degree process. Not required but if you want your engine to be optimal even 1 degree +/- makes a difference.

Lastly I always use ARP screw in studs. I’ve never ever had an issue with them or seen one broken. IMO if you’re upgrading any part of your heads that would be at the top of my list.

Anyway I hope this helps.

-Rascal
 

Bikefixr

Veteran Member
Lifetime Gold Member
Mar 13, 2006
1,883
VORTEC heads have real issues with the retainer hitting the top of the stud boss. Some tolerate a little extra lift, some don't. Past .410, you're taking chances. This really looks like coil bind to me. The coil bound, the valve could go no deeper, and the cam forced the rocker down. It can only go 1 way, sideways, of it pushed the stud out of the way and snaps it off. This is why I always spin the motor by hand to check for clearance. If it all looks good, i back my rockers off. I don't care if they clatter. As long as it runs, I'll set my lifter preload 1 cylinder at a time while it runs. If there is a problem I missed, it shows up then before I ruin everything. When you start shaving heads, mixing rockers (especially self-guided VORTEC's), pushrods, cam's...clearances get sideways really fast. I use a couple adjustable pushrods on my dry setup.
 

kdsracing

Member
Mar 13, 2009
74
Apple Valley, CA
I am rebuilding my 97 k2500 Chevy 5.7 Vortec L31 8th Digit vin R . I had 394,000 miles and decided to rebuild instead of changing parts , got to the point throwing parts at it was getting expensive and time consuming. everything changed out with new stock original parts Cam, Pistons, Heads, Lower intake And upper intake Manifolds, Rocker Arms, Push Rods, Timing Chain, Distributor hell its a brand new engine. the block was bored out .030 over. At start up almost an instant start while setting cam retard at 1000 rpm rocker arm stud broke flush with head. stud changed out and at start up second time setting cam retard a second rocker arm stud broke flush with head on opposite side of engine. if every thing is stock original gm part numbers what the heck is going on. where do i start looking. Any help would be appreciated
Did you install new push rods? Sounds like rocker arm geometry problem. They made push rod checkers that look like a plastic rocker arm that you slide on over the stud then check push rod length.
 




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