Breaking rocker arm studs

JohnnyD

New Member
Aug 6, 2022
7
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
 

ob355

Member
Mar 4, 2022
64
screw in studs? hows it running? could the piston be hitting the valves? what spring pressure are you running? Something got to be a little off.
 

JohnnyD

New Member
Aug 6, 2022
7
Yes screw in studs 3/8 24 7/16 24 runs great sound's solid. No signs of valves hitting pistons. My engine is the last of first generation . i did notice all rocker arms were riding close to the arm tip not the center. I marked all valve tips stems with black marker before doing valve lash . over haul book i have
 

JohnnyD

New Member
Aug 6, 2022
7
Calls for one complete turn after o lash. Every vedio i watch say 1/2 turn. Chevrolet dealer says one turn.now that i have seen travel marks on valve tip my push rods my be too long
 

Twisted_Metal

Administrator
Staff member
Lifetime Gold Member
Feb 26, 2004
31,201
Bloomington, MN
I never do a full turn after zero lash on hydraulic lifter/rocker adjustment... I have always had good results with 1/2 turn + 1 flat. (2/3 turn total.)
That's with the engine running and the lifters pumped up.

Pull a push rod and measure to be sure you have the correct ones.
 

biker

Veteran Member
Gold Member
Dec 7, 2014
4,848
Canada
Your stock GM heads have screw-in studs? Did you perhaps decide to use pushrod guide plates during the rebuild? If so, they are not compatible with factory self-guided rocker arm tips. You can get binding between where the guide plates want the pushrod and where the rocker tip wants to be on the valve stem.

Other possible issue is using factory self-guided rocker arms on valve stems that are not designed for it. The valves that are designed for self-guided rockers have a slightly longer stem tip, and if you dont have those, the rocker self-guiding edges could be hitting the locks at full travel and binding.

Last thing if you dont do this stuff all the time, is to get a truly accurate feel for what exactly is "zero lash" before you tighten down 1/2 turn. The lifter plunger, if not pumped, can be tough to feel zero lash by hand, especially when using a factory locknut.

One more last thing, :) is knowing FOR SURE that you are on the cam base circle for each valve before you go adjusting each valve.

Sorry for the long post, but I only mention these things because I have made all those mistakes over the years.
 

tom3

Veteran Member
Aug 1, 1999
14,506
ohio
Did you use the original bolts in the intake? A too long bolt will hit the pushrod in a couple places, make some problems. Did you remove the studs while rebuilding? Too much torque, impact wrench for removal, something like that? I'd replace all the studs anyway. Do the valve lash while running.
 

JohnnyD

New Member
Aug 6, 2022
7
the lifters were primed and im pretty sure i had zero lash correct before pre load. my first concern was the push rods which call for over all length 7.122 part number gm 10241740 . i ordered this part number from Melling , took push rod to machine shop and was told to be 7.202 . i ordered again from Chevrolet Performance Parts , GM 10241740 but these measure 7.195 even though item shows to be 7.122 im attaching pictures . Notice the dents on the rocker arm edge that has a ridge that can be felt looks like it was hitting edge of valve stem. New intake manifold bolts were used. there are only 8 intake bolts 2 on each corner which are a good distance from push rods
 

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ob355

Member
Mar 4, 2022
64
you have evidence of a very hard impact, you will have to check the geometry of the valve train (pushrod lenght, rocker radio, etc.). Maybe a push rod came out of the socket hit the edge and cause it to bind up. But you have a problem. The valve and the roller are hardened so it was enough force to break the stud. Not the end of the world, but you have a good opportunity to learn. Are the heads new to you?
 




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