340 LA breaking rocker adjuster bolt

[Whitehatspecial]

I am having problems with the #6 cylinder intake rocker adjuster screw breaking. It has happened twice. The ductile Mopar rocker adjuster bolt breaks just before the locking nut (these were new not used when the motor was built 1-1/2 years ago). Mild Comp energy cam, headers, edelbrock performer RPM and edelbrock Thunder series. Fortunately both times this has happened the broken part has stayed on top of the head.
This is not a drag car, street use only. I do jump on it occasionally but nothing crazy.
Ideas???

[422STROKER]

Check to make sure the mating surface on the rocker is perpendicular with the bolt, if it is off the nut will try to bend the adjuster screw.

Tom

[73EStroker]

Did you replace the screw each time and simply continue on? Or did you pull the shaft and check it for round? If it was over tightened then it may be out of round and galling or seizing the rocker up. This would put a lot of extra load on the pushrod and adjuster screw. I have the extra thick wall rocker shafts with the same rockers and I tighten to 25 ft lbs max. 0.586 lift and no problems.

[ntstlgl1970]

Just making sure I understand this correctly, the adjuster breaks off at the top of the rocker, not underneath where the pushrod cup meets the adjuster ball? Like others said, check the spot face of the rocker where the adjuster nut seats and the shaft. Are the rockers pretty old? When you check the adjuster nut seat, see if the threaded hole is really loose to the adjuster bolt, it should be a good fit and not wobble much even before the locknut is tightened.

[Whitehatspecial]

Just making sure I understand this correctly, the adjuster breaks off at the top of the rocker, not underneath where the pushrod cup meets the adjuster ball? Like others said, check the spot face of the rocker where the adjuster nut seats and the shaft. Are the rockers pretty old? When you check the adjuster nut seat, see if the threaded hole is really loose to the adjuster bolt, it should be a good fit and not wobble much even before the locknut is tightened.

The rocker adjuster is breaking off cleanly below the rocker arm, leaving the 1/2" piece that mates to the pushrod floating around on top of the head. The part with the adjuster nut is staying in the arm. Rockers, shafts, lifters and pushrods were new when engine was built about 1000 miles ago.

[ntstlgl1970]

You should only have 2 or 3 adjuster threads showing below the rocker body with the rockers adjusted correctly with the correct length pushrods. Maybe you have more than 2 or 3 threads showing...if so it could be that the pushrod is the wrong length or the valve stem installed height for that cylinder is off which introduces geometry issues. If someone else doesn't post it first, there is a good write up in the mopar engines book about this. I'll try and find it when I get home. Only other thing that might cause this would be coil bind and/or broken spring dampers

[Whitehatspecial]

You should only have 2 or 3 adjuster threads showing below the rocker body with the rockers adjusted correctly with the correct length pushrods. Maybe you have more than 2 or 3 threads showing...if so it could be that the pushrod is the wrong length or the valve stem installed height for that cylinder is off which introduces geometry issues. If someone else doesn't post it first, there is a good write up in the mopar engines book about this. I'll try and find it when I get home. Only other thing that might cause this would be coil bind and/or broken spring dampers

I have only a couple of threads showing below the rocker. I wonder if I'm tightening the locknut too tight that puts separating pressure on the adjuster bolt? I've been using a socket wrench because I can't get an open end wrench in the recessed area of the rocker.

[Changin Gears]

Crane cams, which supplied Mopar Perfomance, had a bad batch of these adjusters about 10-15 years ago.  They would break just like you are describing.

[Whitehatspecial]

Here's a picture. Maybe I have a batch of the crappy ones.

[Changin Gears]

When installed, are the nuts on the top or the bottom of the rocker?

[Whitehatspecial]

The locking nut is on top of the rocker.

[71chally416]

Looks like it was overtightened. 

[440mike]

i asked my boss at work today and here is what he said.
he laughed,
and said alot of guys had that problem way back when, and those guys thought the rockers were hitting the valve cover and busting.

then he said, it is a worn rocker arm thread on that one rocker, or the adjuster thread pitch is to loose on the adjuster screw.

he said it breaks at the top part, just under the adjusting nut, because that is where the most strain is like the teeter totter folcrem, only the longer part of it is the load part, which is loose down throogh the rocker arm, so it breaks right under the nut.

he then said crane had problems way back when, and the fix was a better, deeper pitch thread adjusting screw, which was tighter throogh the rocker arm.

you could send the broken piece back to crane back then, and they would send new ones, but he says they are gone now.

the boss likes it when i ask good questions.
i hope this helps you.

[71chally416]

Helicoil the rocker if that's the case. Thread a new screw in and see if it wobbles.

[Whitehatspecial]

Thanks that makes sense. I wonder if thread locker would work?