Guys, I built my car about 16 years ago. It's a 39 Chevy Business Coupe. My engine choice was a 327, base, with a 2-bbl. I changed to a 4bbl with a year-matching Chevy intake. I drove the car for over 15 years and put on 90,000 miles. Last summer I took it to a very reputable engine builder in Denver and they put on double humper heads, new cam, etc, and turned it into an L79 engine. They installed hydraulic lifters with roller rockers. To keep it brief, after 300 miles, it broke the #6 intake rocker stud. I took it to a local reputable engine builder who found that the pushrods were too long. The pushrods were changed out; a new stud was put in; valves all re-adjusted. So, 200 miles later, the same stud broke again. I took the engine out, hauled it to Denver, and the guys who built the engine "fixed" it. They even gave me an extra rocker stud. (A bad omen, I think.) Finally got the engine back into the car, and discovered that it was noisy. I figured out that the roller rockers were bumping against the valve covers. I put on "tall" finned valve covers and the noise is gone, but I also discovered that the intake was never removed so that the lifters could be checked when the Denver guys "fixed" it. If the #6 lifter is sticking, intermittently, could that cause the stud to break? None of the pushrods were bent. I'm almost afraid to drive it. Any thoughts on what-the-heck is goin' on? Thanx for any ideas.
If they put valve guides in it, make sure the one that is breaking the stud is pressed into the head the proper height. Retainer may be hitting it. D
If you have the old stud, look to see if it broke where the polylock tightens against it. What happens is that they'll use roller rockers and polylocks on a stock length stud, problem is that there isn't enough meat in the stud left to support the lockdown screw in the polylock, the machinest will adjust the rocker, tighten the polylock then doublecheck to discover it is looser than he wants and then he'll wrench the polylock down without loosening the setscrew which pulls the stud apart. Look and see if it is broken right at the end of the stud, also look down into the other polylocks and you'll see if the set screw is way down in there, it shouldn't be. They sell longer studs for roller rockers.
If this is just a street engine. JMO, but I would remove the rockers, put on a set of long slot stock rockers and new pivot balls with new nuts, put my other covers on and go down the road. Once you check it all of course. Sell the roller stuff to pay for your new stuff. Your mileage may vary. I also would have put in screw in studs. Lippy
Basic knowledge needed before the guesswork begins..... what kind of rockers? How much lift? Stock studs or screw ins? Gotta know this stuff before anyone can even have a clue to what the problem is without speculating..... I could be here all day doing that. Pics would be even better
An early fix for pulled studs was to drill and pin the studs it did stop the pulling but weakened the stud. You might check to see if this was done. Is the "extra stud" a screw in stud if so check the alinement of #6 intake stud it might not have been taped straight. As mention in eayler post check coil bind and guide to retainer clearance.
I had a 327 with double hump heads that would wear a groove in one rocker stud and eventually throw the pushrod. After a lot of temporary fixes, I pulled the heads and found the "machinist" had bored one valve guide hole off whack and pressed the guide in crooked. I bet he took a long time to get that valve seat cut.
Usually too much lift and short slot stock rockers cause that, not the guide. Sent from my Moto G Play using The H.A.M.B. mobile app
How much thread from the stud is inside the poly lock? Is it breaking the stud even with the bottom of the poly lock or at the head? SPark
He said he is running an L-79 cam, 350 horse hydraulic. According to the builder. He should have no problems with lift and stock everything. We ran the **** out of them stock day in and day out. I think we have a failure to communicate. and a mismatch of parts possibly? I think GM's idea of a L-79 and his engine builders idea may be two different things. LOL
We safely run up to a .500 lift with nothing more than long slot rockers on round track small blocks with press in studs as the rules had us limited on head modifications. Sounds like your reputable engine builder is having a bad day.
Check out YouTube for running roller rockers and their so called advantage. I think something is misaligned a tad causing this. Stock Chev heads used the holes as guides and the pressed rockers and balls to make up misaligned parts. What do the push rods look like where they go thru the head? We didn't pin our studs; we drilled, bottom taped a 10-32, and used Allen set screws. Kept from drilling thru the stud for the pin.
The possibility of (16) 10-32 set screws in my oiling system makes me cringe! I know, I know, Loc***e.
The Jalopy Journal
