Chevy 250 valve train noise

[250isbestmotor]

I have a 1968 Chevy c10 250 inline with turbo 400 trans I got the tuck 2 years ago the truck sat for 15 years it spun freely when I got it and didn’t take much to get running cleaned out carb and a fuel cell to run it for a bit the truck ran okay for around 6 months had no brakes so just running it in the yard and when to crank it one time and it wouldn’t start had spark and was getting gas I pulled rocker cover and found closest cylinder to fire wall the rocker arm had came off and pushrod was bent I removed side cover and flat tappet lifter appeared fine so I put a one new pushrod in set spun the pushrod and set the lash with one halve turn as Chevy service manual states and truck runs pretty good I’ve done lots of work to motor since then but the rocker sounds like it is about to fly off in the back what could be the issue? Incorrect lash? Or is the head smoked? The rocker arm nut when tighten down is not at the same hight as the rest not sure if this matters any info helps. Thanks https://ibb.co/DDpTC09m image link

[Steeveedee]

Looks like that stud is pulling out of the head. That's a fairly common problem. If it ran OK otherwise and doesn't smoke, you can tap the head for a screw-in stud. If it's smoking maybe just rebuild it? The machine shop can handle tapping the head for a screw-in stud.

[jabborabbo]

Forgive my schoolmarm-ishness, but your post would be a LOT more understandable with some simple punctuation like colons, dashes, semicolons, etc.

Jus’ sayin’….

[RichardJ]

>>I pulled rocker cover and found closest cylinder to fire wall the rocker arm had came off <<

Your picture shows second rocker from the back? #6 Intake. Was that picture taken with the original bent push rod still in place?

In addition to checking the rocker stud height, is that intake valve completely closed and sitting at the same height as the other valves when closed?

"jabborabbo" isn't wrong. Run-on sentences really confuses things.

Spinning the push rod crap isn't a very good way to find "Zero Lash".
If you were adjust valves on a solid lifter, you would slip the feeler gauge ( say .010" ) between the valve stem and the rocker tip. When you are adjusting for Zero Lash, or .000" lash, you adjust the rocker nut until the rocker just touches the valve tip.
IE , flip the rocker tip up-down, while adjusting until the rocker lash closes to .000", then add the 1/2 turn adjustment.

[250isbestmotor]

I apologize for the typing; I got carried away. But yes, that picture was taken when the pushrod was bent. Since I replaced it, it hasn’t bent again. I’ve checked the rocker-stud height with a straightedge, and it’s level. So you’re saying move the pushrod up and down while adjusting it? I find so much different information across the internet on how to set the lash I don’t think I’m doing it correctly thanks for the tip.

[Steeveedee]

Sorry, my mistake on the stud.

[RichardJ]

IF you move the push rod up-down when the adjustment is really loose you could possibly move the rod out of the pocket in the lifter. Pull the tip of rocker up-down where it sits on the valve stem.
That stupid twisting the rod is a GM thing. At least as far as I know. The twisting of the rod could depend on how well the tips of the rod are lubricated or how strong your finger tips are. A new lifter with no oil in it will offer almost no resistance to twisting because the internal spring is very soft. It isn't uncommon for guys with new lifters, tighten the adjustment until the plunger in the lifter bottoms out. Not good.

[70STOVEBOLT]

I followed the “GM thing” and had no issues, have not had to readjust lash since the engine was rebuilt in 2018. Pretty sure GM engineers knew what they were doing. There are several written versions of how to adjust hydraulic lash, and each author believes they are doing it the correct way. I prefer to follow the manufacturer’s recommendations. YMMV

[RichardJ]

>>GM engineers knew what they were doing<<

The GM engineers may know what they are doing, but that doesn't mean everyone reading their instructions has the mechanical aptitude or dexterity to duplicate the process and achieve the same results.

I can see the GM technical writer telling you to twist the rods, but I would expect a GM Engineer to be a little more precise.
Zero Lash is a dimension.

I've been reading various old vehicle forums for about as long as they have been around and one of the most common problems for those with limited mechanical experience, is the inability to correctly adjust hydraulic lifters. Twisting the push rod method is high among those with inconsistent results.

True story:
A guy on a forum with '60s car, made several attempts at adjusting the lifters. He then paid a mechanic to come to his house and make the adjustments, as he observed. Fully enlightened, he wrote a tech article for the do-it-yourselfer and posted it on several locations on the internet to create revenue for himself.

What people read on the internet isn't always the best info.

[Steeveedee]

^ What people read on the internet isn't always the best info. Truer words have never been spoken.

[70STOVEBOLT]

Obviously there is an exact spec. I didn’t read the info on the internet, I got it from the GM overhaul manual. Anyone with basic mechanical knowledge should be able to perform this task. If they do not possess that knowledge, they should not attempt to perform the procedure. I had not actually heard of the spin procedure until I read the manual. I always did it by sound and feel with the engine running. First overhaul and I wanted to get it right, not just close, so I read the manual. I am not trying to be argumentative, just saying that there are multiple ways to achieve the same goal.