Off my rocker ! 350 GM
 

Anyone ever had a rocker arm come off the valve? This motor was rebuild from the ground up and ran fine all last season. It has (twice ) slipped the rocker arm off the valve. Rocker nut had not backed off and preload was correctly set (hydraulic lifters). What should I look for ? Replace the lifter? Camshaft issues? Bent valve stem? Any ideas would be greatly appreciated, Im out of them. Note ,the heads are not original GM by iron "swirl" type. Thankyou

Re: Off my rocker ! 350 GM
 

First thing I notice is how much the rockers are adjusted.
Looks to be showing about double the amount of thread showing on the studs.
Which says you might have the wrong length pushrods. Rockers might be binding on the retainers. And you could need guide plates and/or self aligning rockers.

Re: Off my rocker ! 350 GM
 

^Agree. I've never seen rocker arm studs with that much thread showing. However, since you say it ran fine for some time, a worn/broken push rod end, sticky valve or maybe a worn cam lobe could cause that.

One thing you can do is to turn the engine until the piston is at the top and remove all the parts involved to inspect them. Check to see that the valve moves up and down without binding.

Re: Off my rocker ! 350 GM
 

they could be aftermarket studs which could be longer than stock to accomodate roller rockers. But loose nuts could be a used nut getting in with the new ones. replace the nut, then replace the ball, nut and rocker, also look to see if you've wiped that lobe. By watching the rocker go up and down and comparing it to others and how far up and down they go.

Re: Off my rocker ! 350 GM
 

Post a picture of the hole in the head that the push rod goes through.
Jimmy

Re: Off my rocker ! 350 GM
 

Yes, it's weird that those threads stick out so far. Maybe ok, but it looks odd and draws your attention towards it.

The other thing is the self-locking nuts may be worn and just don't clinch like new ones. I've read that once you run them on and off the studs a few times you need to replace. I know mine feel pretty loose after a few times. I bought a couple of new sets of Cranes.

Also, poly-locks may be a solution.

Re: Off my rocker ! 350 GM
 

Thanks to all for your comments. Based on your comments I had a closer look at the hole in the head where the pushrod exits. There is visible wear on the side of the hole. Not sure what would cause this but definitely the cause ( or effect ) of the failure. The edge of the valve now has a burr which I think I can burnish with a small stone. So … what now? Guide plate ? like they use for roller valve train or someone said that there is a rocker with a centering feature (lip) to prevent side to side movement . Pushrod does not appear to be bent (part #MPR-34-B) Thanks again all for your help

Re: Off my rocker ! 350 GM
 

Good pic in here to show you the difference in rockers.
https://www.thirdgen.org/forums/tech...-arm-self.html

Flip one of yours over and take a pic for us.
Did you happen to check for zero lash when you removed a rocker? Just to see how much preload you have on your lifters. That number might explain the number of threads showing on your studs.

Re: Off my rocker ! 350 GM
 

Sorry I didn't check the lash before I undid it. Thanks for the picture of the self aligning rocker arms. That looks like this would be a simple resolution to my problem. I really don't know a lot about the year of the heads. How many different types (year ranges) am I going to have to pick from. Here is a pic of the offending rocker. The ball is getting ratty (I can feel a burr)

Re: Off my rocker ! 350 GM
 

Get the casting number off the head. It’s partly there in your pic.
Then look here to find out it’s origin.
https://www.mortec.com/castnum.htm

Re: Off my rocker ! 350 GM
 

Here's a similar recent thread.

http://www.67-72chevytrucks.com/vboa...d.php?t=770445

Re: Off my rocker ! 350 GM
 

Wow ! Looks like I got away with only minor damage compared to HO455 ! I was never able to find these heads in any listings casting 14120183 or may be 14120188.

Re: Off my rocker ! 350 GM
 

Those head numbers were discussed here.
http://67-72chevytrucks.com/vboard/s....php?p=7465458

While you have it apart measure the length of your pushrods.

Re: Off my rocker ! 350 GM
 

Hard to tell from the pics bu it does look like when they cut the head for the screw in studs they also opened up the head for push rod clearance. If this is done you need to have guide plates. There are several lengths of rocker studs and it the ones that are in are for roller rockers they are .150 or more longer depending on the ones used.
Jimmy

Re: Off my rocker ! 350 GM
 

Why no guide plates? No wounder the studs look long.

Re: Off my rocker ! 350 GM
 

Studs would look even longer if he had guide plates.

Re: Off my rocker ! 350 GM
 

This is what I was going to say as well. They removed the “guide” that’s machines into the non-screw in stud heads, then drilled and tapped foe studs. Get some guide plates and readjust valve lash.

Re: Off my rocker ! 350 GM
 

That information would confirm or eliminate some competing theories and help us get to the bottom of it.

Re: Off my rocker ! 350 GM
 

Had a closer look at the head of valve , it is quite burred and I am concerned it may not be square to valve as a result of me running it with the rocket off to the side. I have decided to remove the heads and revert back to original style heads (smaller hole). My son will inherit this truck and I don't want something "custom" that has a unique mixture of parts in it (tying him to an engine builder or specialist" . Just walk up to the parts counter and specify 1972 GM .Thanks to all who helped with this issue.

Re: Off my rocker ! 350 GM
 

The burred end would be the valve stem not the head of the valve, so no need to pull the heads.

IMO, Simply fix the end of the stem of the valve, remove screw in studs, install guide plates, reinstall the screw in studs.
"Maybe" buy new screw in studs. Replace the one worn rocker...

Its a intake valve so the bolt that goes thru the intake is not hitting the push rod....intake bolt to long ? NO
No bolt to interfere on this pushrod.
Add rockers and adjust.....

Done.

Re: Off my rocker ! 350 GM
 

That’s likely for the best!
Don’t scrimp when you get different heads. New pushrods and rockers are cheap insurance.
Best of luck!

Re: Off my rocker ! 350 GM
 

Often times the more stock the better, especially when it comes to future upkeep and maintenance.