My sbc 350 is bored .40 over and only has about 2 hours on the engine. What causes this? I started it and let it run for 10 minutes and this happened.
Rebuilt the 350 in my 70 camaro years ago, broke it in easy for a couple hundred miles, first time I nailed it, broke two rocker studs. Scratched my head probably the same way you are, replaced the studs and never had another problem. Looks from the photo that the rocker tip is centered on the valve stem. Maybe just a bad stud?
Can only imagine the strange noises that made when it went , but really that sucks, means your not driving till it's fixed.
You can run the gauntlet of Checks and elimination. Binding geometry. Excessive spring pressure/ valve lift Mechanical bind in the valve, valve spring, cup, or rocker. Tired old stud
Had one break on my vortec heads.....had roller rockers and poly locks on it and thats what kept rocker in place, just a little noisy. Might have had a couple thousand miles on screw in studs....beehive springs and small hyd cam
The push rod rolls smooth on counter top, which is good. The heads are from 86' and I believe with original "pressed in" studs.
if you have a big cam or high spring preasure,that can cause it other wise the press in the casting just gets weak over time and you have to pin the studs or thread the holes and go back with screw in studs
from the pix in post #10 .It look's like the polylock is not screwed in that much. you might need shorter pushrods ,get more threads in the polylock. after you change the stud.
I was successful this morning with removing the stud partially. I stacked 3/16 ss washers over the stud and ran a nut down and continued to add washers as it was extracting. I unscrewed the poly lock and only 3/8 of an inch of the stud snapped off. How hard is it to press in the new stud?? Can I leave this stud and just keep it pulled up the 3/8??
When you build a new engine with different cam ect., it is important to put a head together with a one cylinder using the valve train parts you selected. Carefully check things like coil bind, pushrod length and clearence between retainers and rocker arms. Also look for stem seals touching the inside of the springs at full open. On Chevy heads do not mix self aligning rocker arms with guide plates. Just a few random thoughts learned the hard way.
No you can't leave it up !! 3/8 of thread into the Polly lock isn't quite enough in my opinion. Like was said, check your pushrod length. I think you have geometry issues. The Polly lock should be threaded on further . It's not that difficult to install new studs. Put them in the freezer for an hour or two. Also not that difficult to up size and use screw in studs.
I'm in agreement with 31 Vicky, if the tip only broke off it is because the poly lock was only screwed on that far and it "worked" the tip of the stud until it snapped. Something is screwed up in the geometry, like too long pushrods. We snapped off a valve in the 302 in my Son's T bucket for that very reason. We had used too long pushrods and since the studs were thicker screw in studs they took the abuse but it snapped a valve off. We replaced all the pushrods with the right length and no more problems. Don
If you are seriously asking questions such as this one you have no business tackling any motor work. As it was said before check all of your geometry, clearances etc. I would bet you have coil bind or pushrod length issues. Probably the later as you only had a little bit of the stud in the lock nut.
Certainly does not appear sarcastic in anyway the way the question is posed. Someone put the poly locks on like that and bolted the valve covers on.
Lets see no guide plates? Late heads if I recall can't use an early rocker are your rockers '86 and newer specific? These are just questions that you can ask yourself. I have never run roller rockers without guide plates, that will involve molly pushrods and drilling out the holes for the rockers. or you can use the original pushrods if you get the manley fiber guidee plates.
what lift is the cam? I still say coil bind, the late model heads do not have much extra room between the valve guide seal and retainer and that looks like a stock or z28 spring.
In your picture, it looks like the rocker arm on the left side of the picture has some marks like it may be hitting the poly lock nut. If your push rods are too long, the rocker arm will be at an extreme angle when the valve opens. The rocker hits the polylock and tries to bend the stud. To install the new stud, put a nut on the stud to drive it in with, cool the stud with dry ice if available or in a freezer. Slightly warm the stud pocket with a torch.
Here is some good info for all studs and bolts. You should have at least 1 1/2 X the diameter of the bolt/stud engaged in the nut or what ever it is screwing into. In other words, a 1/2" bolt should screw in at least 3/4" to achieve full holding strength. JC
I hope you got it all going again, never would have guessed a geometry issue with installing roller rockers, guess that's how it works with after-market parts, got to check out everything possible before turning the key... May the road gremlins flee as the roar of a healthy V8 puts fear in their eyes!
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