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Thread: I Keep Breaking Rocker Arm Studs

  1. #1
    MidnightMantra
    Last 3 times out I have broke the rocker arm studs on the #2 cylinder. I am running a 468 BBC with a large roller cam. 310 Dur with .714 lift. After the second time I checked to see if the springs were bottoming out but there was .74 thousands gap between each spring coil. That should be sufficient. I noticed that this particular bank steams more out the headers than the other. This has always happend at 3500 rpm cruising speed on a long run. Is it possible that water is getting sucked into the cylinder somehow at this speed and compressing the water and not allowing the valve's to open and breaking the studs? I am running the banderlog valve so no water is coming out till 2000 rpm's. I am going to put new studs in again this weekend and run the headers dry. Process of elimination I guess. What is your unputs?

  2. #2
    Kachina26
    I would think the pushrods would bend before the rocker arm studs broke if it were water in the cyl. both studs?

  3. #3
    MidnightMantra
    Yes both studs are breaking, I have hardened 7/16 push rods. I am amazed myself that the rods have not bent. They are as straight as can be.

  4. #4
    Ken F
    How much spring pressure do you have? If your springs are spec for a car, chances are that they are way over what you need to turn 5-5500 rpm. Are you running stud girdles?
    I've had the same problem running about the same lift only on a BBF.
    I made special studs out of the strongest steel made, and still broke them.
    Stud girdles solved the problem.
    Ken F

  5. #5
    steelcomp
    few questions...
    what heads
    what rockers are you running
    what rocker studs are you running
    what spring pressures
    what rpm
    where are the studs breaking
    You're not sucking water in at that rpm...not enough to hurt anything. You've got something else going on. Most likely a geometry prob. If you had that much water in a cyl while it's running, you'd bend a rod...or more.
    Have you checked the clearance between the bottom of the retainer and the top of the guide? How 'bout the inner spring(s)?
    How's the alignment between the tip of the rocker and the tip of the valve?
    start there.

  6. #6
    MidnightMantra
    yes ken, This engine came out of my old drag car. Motor used to just run 1/4 mile only. No girdles, studs could be getting hot on long runs causing flex then snapping. That is a possibility.

  7. #7
    MidnightMantra
    dart heads, arp rocker arm studs, comp cams race push rods, comp springs with comp rockers, geomety looks good, valve fully open i have .74 thousands of clearance between spring coils, stud always snaps at base of the lock nuts. All this only on cyl #2 . I cruise at 3500 rpms and WOT at 5400 rpms. Never happned at WOT, always after a 10 mile run or so at 3500 cruise speed.

  8. #8
    steelcomp
    for some reason(s) there must be a harmonic vibration being set up in that cyl...cam lobes, cyl pressure, springs,...who knows. Stud bosses could be machined slightly off (stranger things have happened)
    It's not the material...ARP is the best. If they were getting hot enough to work, then snap, you'd have other problems, and it wouldn't be isolated to one cyl. They ARE getting hot and snapping, but heat isn't the culprit. It's the result of them bending, like when you bend a piece of coat hanger, due to the harmonic vibration. Stud girdles are pretty much mandatory on alum heads w/ big rollers. Surprised you haven't broken a stud boss. I'd definately run a girdle...this will definately stop the breakage. You never ran it long enough for this to happen if you just 1/4 mile'd the motor. Probably tached right through the problem. The girdle will help stop some of the movement, and also absorb and distribute the frequency. You'd be surprised at how much smoother your motor will run. Cut your valve lash down to .016/.018, or .018/.020 hot. This will also help reduce unwanted valve train vibration, and help reduce valve bounce. This can be worth good hp, depending on how much you're already making.
    steel

  9. #9
    MidnightMantra
    thanks for the input steelcomp. I am going to order me a girdle kit from Summit tommorrow. I gotta fix this problem, tired of getting towed in.

  10. #10
    MidnightMantra
    The cam is a solid roller, The heads have only been shaved to make them true. I have checked all anlge if contact with the rocker and everything is clear and has pleanty clearance. I think that I agree with steelcomp. The rocker studs are flexing casuing them to snap. Expecially with the amount of lift I am running. I am going to install a girdle kit and go from there. The last time out I ran the boat for about 3 hrs before the stud broke this time. what gets me it always happens at cruising speed 3500 rpms on a long run and not at WOT.

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