78pace

What would cause a rocker arm screw in stud bolt to break? In late
July had a shop install Edelbrock RPM Power Package .Went with Comp Cams 12-660-47 cam. Comp Cam roller tip rockers. Car was idling poorly checked a few things and decided to pull the valve cover. What I found was the broken stud.....

7T1vette

If they added some stiffer valve springs but didn't replace the [40 year old] rocker studs, that might be one reason. If that's the case, you can put a new stud in to replace the broken one...but that probably won't be the last stud that breaks.

78pace

Should have added these were new completed heads. edelbrock 60899 aluminum heads.

DRIVESHAFT

Where did the stud break?

78pace

Broke just below the bottom of the nut......Just where the threads end and bolt is smooth

bobs77vet

poor valve train geometry......maybe the pushrod was too long or too short when you get the stud replaced be sure to check alignment. the blue thing slips over the stud and should touch both valve and pushrod at the same time....and you adjust the push rod length if necessary by getting different length pushrods

78pace

I did get +1.00 on the push rods...per Edelbrock. What is the blue thing called I will pick one up...thanks to all found it proform makes one......

GUSTO14

Related to Bob's comment on valve train geometry is the length of the slot in the rocker. Look at the rocker (from the broken stud) for evidence that the rocker is bottoming on the stud when the valve is at fully open or fully closed.

Back in the day before everyone began to run full roller rockers, when swapping a higher lift cam into a SBC or SBF engine with stock rockers it was not unusual to encounter this problem. What we discovered was that the variance on the slots in the factory stamped steel rockers could be as much as 30 degrees (from the longest to the shortest slot). You could either enlarge the slot (picking the longest slot and matching the rest to it was always safe) or step up to full roller rockers.

Good luck... GUSTO

Indiancreek

Gusto14 brought back some memories. We used to have to lengthen the slot so there was room for the higher lift cams. Check if you have some half moon looking marks on the rest of your studs.

L88Plus

I had two break on a pair of Trick Flows. Replaced those and never had any more troubles. Bad out of the box was my diagnosis.
Still have a few replacements - 7/16 bottom / 3/8" top if you need 'em.

78pace

Thanks, L88Plus ...spoke with Edelbrock and they are sending a pack of 2.

BLOCKMAN

There are some studs that have cut threads rather then rolled threads. I would go to an ARP studs and be done with the breakage!

thegazman

birdsmith

AND, if you buy 'em direct from ARP they will send you nifty Christmas cards too!

Surfer69

Just a word about studs....

I bought a brand new set and one broke like yours. Called AFR and they admitted they had a bad material batch made (not sure if they were ARP) but sold them anyway. They replaced my whole set for free...

but you never know so just keep an eye out and if another stud breaks you know it's bad material.

Kerrmudgeon

This! Metal fatigue is hard to diagnose. You never know when a part is going to fail with time. Do the one side at least since you have it open. Loctite on the threads.

427Hotrod

How many threads were engaged in the adjuster? Got any pics?


JIM

78pace

I counted 5 threads from top of stud to top of adjuster.......

427Hotrod

You want the rocker to operate down in the shank area of the stud and the adjuster to grab as many threads as possible. If it's really taking those .100" long pushrods to get geometry correct (need to actually ck and measure) then likely you need longer studs also. Only using a few threads is a recipe for failure.

JIM

pauldana

valve spring binding... check your seat height both open and closed... check what it is supposed to be speced out to.... bet that's the problem.... been there. done that... p:-)