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rocker stud breaking

General engine tech -- Drag Racing to Circle Track

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Belgian1979
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rocker stud breaking

Post by Belgian1979 » Sat Oct 12, 2019 2:52 pm

I had to help a friend today that got stranded with his Corvette. The engine was seriously spitting back through the intake and he put it on the side of the road. I suspected a valve issue of sorts and took of the rocker covers. One of the rockers was lying loose under the right (cyl 8 exhaust) and the stud of the rocker had sheared clean off. Not sure what happened with it. Haven't seen this before. It was a clean break, apparently just below the rocker. Any idea about what can cause this.
He took out the plug and push rod and drove it back home over something like 2 miles. I advised against this as I was afraid that the lifter might come out of the bore and it would loose oil pressure. He did it nonetheless.

Carnut1
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Re: rocker stud breaking

Post by Carnut1 » Sat Oct 12, 2019 3:18 pm

Early 90's I did not know what a redline was so I broke plenty of studs before I realized I was asking too much from the valve springs and was going into surge and at times float. When the spring finally catches up the forces go through the roof.
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Belgian1979
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Re: rocker stud breaking

Post by Belgian1979 » Sat Oct 12, 2019 3:36 pm

That was my first guess, so I told him to keep the rpms within reason...

Carnut1
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Re: rocker stud breaking

Post by Carnut1 » Sat Oct 12, 2019 4:14 pm

Belgian1979 wrote:
Sat Oct 12, 2019 3:36 pm
That was my first guess, so I told him to keep the rpms within reason...
The problem with spring surge or float is it overheats the springs very fast. Once they heat they lose load and then surge or float even easier. Testing those springs is probably a good idea. Thanks, Charlie
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BillK
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Re: rocker stud breaking

Post by BillK » Sat Oct 12, 2019 7:38 pm

What engine ?
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Belgian1979
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Re: rocker stud breaking

Post by Belgian1979 » Sun Oct 13, 2019 3:03 am

350 SBC gen I

bobmc
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Re: rocker stud breaking

Post by bobmc » Sun Oct 13, 2019 5:34 pm

is this with ball rockers or roller rockers?

jsgarage
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Re: rocker stud breaking

Post by jsgarage » Sun Oct 13, 2019 9:52 pm

Rocker stud girdles are cheap insurance with a small price in adjustment convenience.

Belgian1979
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Re: rocker stud breaking

Post by Belgian1979 » Mon Oct 14, 2019 1:44 pm

Roller rockers. It's not my engine, so I didn't make the choice. I run shaft rockers.

Dan Timberlake
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Re: rocker stud breaking

Post by Dan Timberlake » Mon Oct 14, 2019 6:46 pm

Can you get some nice closeups of the stud fracture surface?

ProPower engines
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Re: rocker stud breaking

Post by ProPower engines » Mon Oct 14, 2019 7:35 pm

If the spring choice is combined with stock replacement or just stock 3/8 studs and they will break in time.
If he is using stock rockers check for binding against the other studs. Rollers will flex a cheaper stud alot with a good
spring. Even decent single stock OD springs will cause stud flex up to .050 from what I have seen and studs don't
like to flex much so they fracture and break.

If he drives it hard he needs to know he should upgrade his valve train or this can happen more often.

At very least the thing to do at this point is change ALL the studs as I am sure the others are not far behind
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