Broken Rocker Studs... Why?

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SRS_Chris
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Broken Rocker Studs... Why?

Post by SRS_Chris »

A customer has broken two rocker studs in the past week and I'm not sure why. Any ideas? Here are the details...

GM 383HT crate engine. Vortec "060" heads with factory hydraulic roller cam.
We changed the cam to a hydraulic roller that has .495" lift with the 1.5 ratio rockers. We changed the valve springs to a Comp beehive that has about 145 on the seat and 340 over the nose.

There is about .045" seal to retainer clearance. There is also clearance in the rocker slot. The pushrods are staying straight in the holes that broke studs. There is plenty of piston to valve clearance. I ran this car on the chassis dyno after the cam and springs were changed and it ran well. The valvetrain was whisper quiet.

Both studs broke in the same place; about two to three threads up from the base of the threads on the stud. This is almost flush with the bottom of the jamb/adjusting nut on the rocker arm.

What am I missing? What might be causing this? The heads are off and I am converting all studs to screw in pieces. I am also changing to a full roller rocker arm (still a 1.5 ratio) to try to take some stress off of the stud. The valve seal boss will also be cut down to give some more seal to retainer clearance.
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Re: Broken Rocker Studs... Why?

Post by ProPower engines »

Threaded or press in studs??
They may be inferior quality studs if they are threaded. I see that alot when guys buy crate engines that uses the vortec head with threaded studs in marine applications.
Sometimes the studs break that are pressed in as well as some heads when assembled do not have enough room before coil bind with the stock springs and the studs take a beating or bend push rods as well.
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Re: Broken Rocker Studs... Why?

Post by shoedoos »

is it a posilock or a nut as per OEM for adjustment? If its a posi is there a chance the set screw is too tight and heat expansion is popping the threads?
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Re: Broken Rocker Studs... Why?

Post by Geoff2 »

I have seen studs break for no apparent reason. No binding or other problem in the valve train. The studs do flex with the spring pressure, so the metallurgy needs to be good.
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Re: Broken Rocker Studs... Why?

Post by midnightbluS10 »

You were still using the stock, non-adjustable Vortec rockers when the studs broke? Roller trunnion with non-roller tip?
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Re: Broken Rocker Studs... Why?

Post by BOOT »

First what size stud?

Is this a power adder engine and if so is it the exhaust studs?
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Re: Broken Rocker Studs... Why?

Post by 427dart »

Maybe swap to ARP screw in studs?
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Re: Broken Rocker Studs... Why?

Post by Steve Haaf »

Sounds like they are press in studs, when you have to convert to screw in studs. Looks like you found the limits of stock factory studs, with that seat pressure, it`s a wonder that you`re not jacking the studs out of the heads. If you`re buying new studs and rockers then upgrade to ARP 7/16 studs and rockers, they`re the same price as 3/8s. Maybe talk to Ken Brown in Summerland for your machine work, he has the experience and machines to do the job for you.
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Re: Broken Rocker Studs... Why?

Post by fdicrasto »

Had this type of issue with a bbc marine app that was an A-production race boat many moons ago. Every race would end with a few studs breaking in various positions. After a few aftermarket replacements failed went to arp studs and never a failure again.
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Re: Broken Rocker Studs... Why?

Post by SRS_Chris »

ProPower engines wrote: Tue Jul 10, 2018 12:56 am Threaded or press in studs??
Press in
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Re: Broken Rocker Studs... Why?

Post by SRS_Chris »

shoedoos wrote: Tue Jul 10, 2018 1:11 am is it a posilock or a nut as per OEM for adjustment? If its a posi is there a chance the set screw is too tight and heat expansion is popping the threads?
The issue was occurring with the stock style nuts.
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Re: Broken Rocker Studs... Why?

Post by SRS_Chris »

midnightbluS10 wrote: Tue Jul 10, 2018 6:13 am You were still using the stock, non-adjustable Vortec rockers when the studs broke? Roller trunnion with non-roller tip?
They were adjustable style, self-aligning, 'ball and socket' (non roller tip, non roller pivot) style rockers.
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Re: Broken Rocker Studs... Why?

Post by SRS_Chris »

BOOT wrote: Tue Jul 10, 2018 6:18 am First what size stud?

Is this a power adder engine and if so is it the exhaust studs?
3/8" stud

Naturally aspirated engine. Not a real power house by any means. The two studs that broke were both intake studs.
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Re: Broken Rocker Studs... Why?

Post by pamotorman »

sounds like a bad heat treat and they are too hard.
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Re: Broken Rocker Studs... Why?

Post by cardo0 »

The rocker arms need to be checked for clearance. Clearance of the stud and spring retainer. An unbent paper clip works for this if thick enough. Crane came tech info explains this. Most owners expect valvetrain parts are just bolt on and go and find the bad results later.
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