Don Terrill’s Speed-Talk

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.

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.

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

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

What engine ?

350 SBC gen I

is this with ball rockers or roller rockers?

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

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

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

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

I will tell him when I see him again. I can't take any photos at the moment as it's not my car and not here.

Just let him know that if they are generic studs they are not the best choice for durability and strength.
He will get by with a simple fix of changing the busted stud but make him understand they are doomed to fail again and
the damage that can be caused could be catastrophic if the rocker jams a valve open at the wrong time.

I would not dare comment until the fractured stud and the rocker assembly was available for inspection.

https://www.goodreads.com/quotes/92128- ... re-one-has

Rocker studs breaking with roller rockers, can often be traced to the rocker arm roller tip running off the end of the valve. Shorten the pushrods to avoid this.