I had a broken rocker stud on #1 cylinder intake valve. It was a press in, and I replaced it with a threaded stud, Mr Gasket 1076. It's tight in the bore, no issues. The pushrod was a tiny bit not straight, so I replaced it as well. Also replaced the nut. The rocker arm and pivot are original.
So I'm setting the valve lash using the running engine method, loosen till it ticks, tighten till it stops, then 3/4 turn. The issue is, it doesn't feel like much torque. The others tighten up with good resistance and stay. This one is good for a min, then ticks again, and it's loose. Tighten it up, runs good, few minutes, it's loose again. The stud isn't pulling out, the nut isn't loosening up, I'm just having to thread it down more and more.
I guess the question is, when you torque a rocker arm nut, what are you torquing against? Is it the rocker against the shoulder on the stud? Is it the pivot against the shoulder on the stud? Is it the rocker arm against the pushrod?
Any ideas why it just won't torque down and keeps coming loose? Could it be the rocker arm hole worn from the broken stud? Or the stud is too short? Maybe a collapsed lifter?

 

Sounds like a bad lifter to Me. You already determined that the stud isn't pulling, and the nut isn't coming loose. There's nothing else that could increase the lash...

 

I'm starting to think that too. I guess my question is general engine physics. When you're setting valve lash, and you're torquing the nut, are you torquing against the pushrod?

 

I'd set it NON running https://www.motortrend.com/how-to/ccrp-0702-camshaft/

Back it off n let it sit maybe over night, so hopefully the lifter decompresses since they do have a small internal spring. Then set it but careful to not compress it when going to zero lash before adding the preload.

My C4 has a few not so great lifters but it has 90k on it. If I rem right this was just a 305 or 305 heads at least, how hard are you running it?

 

Paint a stripe on the rocker nut and do your adjustment again.
Revisit the adjustment when the ticking re-occurs.
If the stripe hasn't moved, as suggested, it's probably the lifter that's giving up.

You might do yourself a favour and also try the lash adjustment without the engine running. You can get a better "feel" for what's going on. Just be sure you follow the proper procedure.

 

I agree with the above two posts. There's really no benefit to adjusting them with the engine running. Just take it to zero lash on the base circle of the cam lobe, and add preload...

 

With the stock rocker nuts, you are torquing against the nut. They are slightly crimped/deformed to upset the threads inside of the nut. This is what prevents, or is supposed to prevent, them from backing off.

If you can get another rocker nut, then do that replacing the current one. If not, see if you have a nut with the same threads and double nut the current one. That too will prevent it from backing off.

RBob.

 

As a followup, if the nut is truly not backing off, but keeps going back to ticking, I'd say the cam lobe/lifter is going away. IOW, the cam is going flat.

RBob.

 

Definitely not running it hard. It's just a driver. Stock 305, stock heads.

 

No, I mean I do the adjustment, and within 2 mins it's ticking again. The nut is definitely not backing off.
I've actually done it both ways with this engine. First non running, then running. Really the same outcome with this particular rocker.

 

Actually tried two new nuts, same outcome. And the stud is new and not backing off. The more I talk it out, the more I think its gotta be the lifter.

 

A couple of things you might investigate seeing as it appears either the lifter is giving up and the lobe is slowly eroding.
With that particular lifter on the base circle, can you easily push down on the pushrod and collapse the lifter? Compare it to one that keeps it's adjustment.
The other is to check for metal in the oil.
I would like to think that the hydraulic assembly in that one lifter is on the way out. But the broken stud could be very telling on the lobe department too. Any component separation in the valvetrain can wreak havoc with a stud snapping being the end result.
FWIW, I hd a rocker stud snap off while cruising on the highway. Maybe 2500 RPM tops and bang! Whatever the chain of events it was that caused it to break, it left a witness mark in the rocker cover in the form of a bulge.

 

Next question what oil are you running? Some get by with thicker oil, like 10w40

Still plenty of engines with ticking lifters, flat tappet or roller. My 2009 Silverado ticks. My 86 C4 if your not careful like 3 of the lifters will compress trying to get to zero lash, I plan to do something bout that but I shift it at 6k with 1.7 rockers

If it hadn't broke the stud I'd dismiss the bad lifter/cam suggestion But again it's just a daily driver 305, set preload, cut your oil filters to check for metal n keep an eye on it. https://www.motortrend.com/how-to/ti...etrain-issues/

It was an intake stud so can't blame the exhaust side, how did the spark plug look? Could be just the stud was defective then time & bad luck and it never causes an issue again. I mean how deep yah wanna go? Is the engine worth upgrades/other new parts?

 

Are you absolutely sure the new screw in stud is not backing out? Have you marked the stud and marked the nut after adjusting the lash, then see if either or both have turned when the ticking starts again? If you confirm that is not happening, then I would agree that it's probably a bad lifter and/or bad camshaft.

 

Just running 10/30 with some zinc.
Spark plug looked fine.

 

The stud is definitely not backing out, its still screwed in tight in the boss.
The nut isnt backing off either. Its funny, when im setting lash non running on the other rockers, when you get to zero lash and give it the final 1/2 turn, you can feel the torque on the nut; it gets harder to turn.
On the problem nut, i can go to zero lash, and the last 1/2 turn there is like very little resistance. I can continue turning the nut way down, until it starts opening the valve, before i feel resistance.

 

So i can tighten the nut until the pushrod stops moving in my fingers and give it 1/2 turn. Double the threads are showing on the stud at this point compared to the others, and the nut isnt very tight. Start the engine, and its quiet and steady on the vacuum needle for about 2 mins, then starts ticking and its loose again. If i continue tightening, eventually the rocker starts to drive the valve open and it runs terrible, as you would think.
So im just thinking its a lifter issue. I can never really set the lash, because the lifter is collapsed.
Could be the cam lobe too, but im thinking positive at the moment.

 

While some of the resistance to turning the adjusting nut comes from the locknut itself, part of it is also trying to overcome the hydraulic pressure that's in the lifter. Or should be. This is in the preload phase after zero lash has been achieved,
If you can push down on the pushrod and collapse the lifter more easily than a proper functioning one, you've probably zeroed in your problem.

 

This is what i was thinking. Tightening the nut is torquing the arm against the pushrod, pushing against the pressure in the lifter. No resistance in the nut, means im just shoving the pushrod into a collapsed lifter. At least thats how i understand it.
When i crank the engine, the cam is lifting the dead lifter up and down and eventually the rocker arm is loose again. I can tighten it more and more, but eventually, im just pushing the rocker against the valve spring, and then its hanging the valve open.

 

A dead lifter sounds like the next logical diagnosis. I'm assuming its a flat tappet, not a roller. For flat tappets, I have always changed the cam and lifters as a matched set. Perhaps others with experience can chime in as to whether they have had success with only changing out one lifter and keeping the cam (assuming the cam lobe looks good). Would be a lot easier than a full cam swap, but not good if it chews up the cam lobe.

 

Bad lifter or possible a wiped out cam lobe.

Technically, there is no "torque" on the rocker nut. The nut itself is sort of a stover type nut and should not loosen off by itself unless it is worn out. When tightening the nut, all you are doing is adding preload to the lifter. Engine off and lifter is sitting on the base circle of the camshaft. Rocker is backed off. Start tightening the rocker nut until the pushrod just stops wiggling around. This is about as close to zero preload as you can get. Rocker/nut/pushrod are all making as minimal contact as possible and the plunger inside the lifter has not been compressed.

Now for the preload. Technically you want 0.015 - 0.020" of preload in the lifter for it to work properly. That means tightening the rocker nut anywhere from 1/4 to 3/4 of a turn. One end of the rocker is already making contact with the valve tip so the other end of the rocker is pushed down on the pushrod and into the lifter. After the preload is set, the pushrod will feel loose again as the lifter resets. No not tighten any more for more preload!!

I would check the lifter/cam lobe before trying to adjust the rockers. You cay you had a slightly bent pushrod. That's never a good sign.

 

Just kind of a followup for anyone interested.
Luckily it was the #1 cylinder, so there is an oil passage right above it. I hit it with some Seafoam and let it sit for a few days. I went ahead and replaced the rocker arm, pivot, nut, and pushrod. I let it run and hit it with more Seafoam to try to flush it out. Reset the lash, and its improved, was able to feel resistance now on the nut, whereas before the nut would just thread down with no resistance. The nut is showing more thread than its neighbors, but its much improved. Compression test on that cylinder shows 180.
Put a few miles on it and its quiet and happy so far. Im hoping there was just maybe some trash in the lifter passage that flushed out. Im going to change the oil and put some miles on it if it stays quiet, then maybe pull the valve cover in a bit and check the lash again.

 

That's not a good sign. I think you've put a bandaid on a major surgery problem. Keep us informed when the engine fails again.