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Discussion Starter #1
the other day i was going up a hill at a low rpm and i heard a popping out of the carburetor. i than pull the valve cover off and it broke a screw in stud. i replaced it and put it back together after checking everything. again today i was backin up a hill same thing happened and the stud broke and on the valve next to it it bent the pushrod. what could this be it has sportsman II heads the springs are not coil binding. it has a lunati voodoo cam and it is set dot to dot on timing chain. it also has the correct installed height and 1.5 ratio stock rocker arms. p.s the stud breaks in the same spot where the threads start.
 

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how much margin do you have on the springs? by that i mean, how much lift can your springs tolerate vs how much lift you have. Also, check the retainer to valve guide box clearance.

Also, does the slot in the rockers have enough clearance?
 

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My guess is the rocker arms are binding in the slot. Double check coil bind clearance and retainer to guide clearance also but I'll bet it's the stock rockers. They don't have enough slot for most high lift cams. You at least need long slot rockers.
 

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Discussion Starter #4
the slot in the rocker arm is what me and my dad were thinking.they are stock rockers. when the valve is close the rocker arms is touching hard against the stud. when it is down there is room to spare. is it normal for it to be touchin when the valve is closed? also there is not coil bind happening. the cam is a .525/.546 lift. i have a .100 longer valve and not push rods. when the valve is up it only contacts a little more than half the top of the valve stem. i have .100 longer push rods ordered. do you think that would affect anything?
 

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71nova said:
the slot in the rocker arm is what me and my dad were thinking.they are stock rockers. when the valve is close the rocker arms is touching hard against the stud. when it is down there is room to spare. is it normal for it to be touchin when the valve is closed? also there is not coil bind happening. the cam is a .525/.546 lift. i have a .100 longer valve and not push rods. when the valve is up it only contacts a little more than half the top of the valve stem. i have .100 longer push rods ordered. do you think that would affect anything?
Yes, it will! Aftermarket valvetrain parts often change valve train geometry.
You're finding out what happens when you mix parts/

Basically you need to make sure your rocker is in the center of the valve tip when it's at mid lift. Color the tip with a Marker and bar the engine over. You'll see the contact pattern.

Don't assume the push rod length needs to be equal to the stem length. Get an adjustable pushrod and figure out what length gives you the best contact pattern.

Stock rockers won't work with that much lift. Get long slot rockers or rollers.

Don't assume all rocker studs are all the same either. Certain rockers need specific studs. Make sure if you change to a different rocker type you get the compatable stud. For example GMPP self aligning roller rockers have a unique stud. Roller locking nuts require a machined flat top. Studs that are for stock self lockers have an irregular top.
You also don't want the rocker ball to ride on the threaded portion. It should ride on the smooth shank.
 

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I hate that when surprises come up at the end when your thinking your saving money and it doesn't work - then you pay even more.

I was planning on using stamped rockers with longer slots but after putting them up next to the 1.43 od springs I wasn't comfortable with it. Ended up forking out $ I didn't have to get some nice S/S rockers from Speed-O-Motive.
 

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Discussion Starter #8
i just ordered roller rockers. and longer push rods. it will be here tomorrow. ill have to see how it goes. thanks for all the advice. also i called lunati and they also said the rocker arms were wrong.
 

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Discussion Starter #9
just keeping you guys informed that i installed the roller rockers and longer push rods and everything is working perfect. no more broken studs.
 
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