this may be a strange question, but i just want a second opinion.i have a 69 chevy c10 350 with a 4bb carb and hei ignition that i found out has two notched rocker arm studs due to loose rockers.i have adjusted them and removed slack.but now i have a constant tapping noise from that head due to the notched studs. my mechanic has “advised” me not to bother replacing them in order to save me money, which i appreciate. my question is what damage, if any, will i do if i chose to do this? he mentioned the worst that will happen is if the stud snaps it will only fire on 7 instead of 8!? does this make any sense?
What does the HEI Ignition or carb have to do with the notched rocker arm studs???
Replacing Rocker Arm studs can be difficult. You might have to take the heads off and take it to a machine shop. Although I have done it myself on a 327 years ago.
If you don’t drive much the tapping isn’t going to really hurt much. I wouldn’t fix it unless this is a show vehicle.
There’s a lot of thihgs that can happen if this is allowed to continue without a proper repair. When the stud breaks it’s possible the rocker arm and/or push rod can come through the valve cover, rocker arm or stud parts could wind up wedged into another rocker arm and do who knows what, and chronic valve train tapping will destroy the valve lifter face (probably already done) and this in turn will ruin the cam lobes(s) by causing them to go flat not to mention ruing the pushrods.
It seems to me it’s much cheaper to fix it now rather than later so I disagree that the only problem will simply be a dead cylinder (which will certainly occur.)
ok…this is what i figured. i have gotten a couple of estimates on replacing the both heads just as a precaution, but seems pretty high in comparision of replacing pressed in studs with screw in studs. either way the head has to come off. or does it?
tmi i guess. not much of a daily driver though.only used for quick errands thats pretty much it.other than this problem i am maintaining the engine best i can through preventative maintance. is this enough? ( i will eventually replace head or studs whichever i can do cheaper, some time down the road)
The studs can be replaced with the heads in place but it does require a special tool.
There is also a pinning kit available that should be used for replacement press-in studs.
Another option is to drill and tap the holes and use screw-in studs.
Considering the age of the engine and a couple of problem studs what I would do if the engine were mine is remove all of the rocker arms, push rods, and valve lifters for inspection and install a full set of screw-in studs.
Push rod ends should be examined very closely for flaking or near microscopic cracking and the valve lifter faces should be examined very closely.
The valve lifter faces should be domed slightly but this is not something you will see at first glance.
The way I check the lifter faces is by placing the sharp edge of a new single edge razor blade across the middle of the lifter face. Hold it up to a good light.
With a good lifter face you should see a tiny sliver of light around the edges of the lifter face. If you see a tiny sliver of light in the middle of the face, and not on the edges, the lifter is worn out. When they get like this they do not rotate as they should, and indirectly, do not cause the valve in the head to rotate a bit either.
Hope that helps.
“…When they get like this they do not rotate as they should, and indirectly, do not cause the valve in the head to rotate a bit either.”
So the rotating lifter would normally spin the pushrod, the spin somehow goes through the rocker arm and spins the valve in its guide too?
Not directly from the actions of the pushrod, no. But the valve should rotate a tiny bit. Of course, this is so slight as to never be noticeable. As the rocker arm contacts the valve stem it does not push straight down for the entire distance of the valve lift; it has a tendency to pull a tiny bit sideways (again so slight as to not be noticeable) and this can rotate the valve. This stuff was explained to me in a service school one time but that was about 25 years? ago and as far as valve rotation is concerned it could be considered irrelevant minutae. It’s a bit more prevalent on some overhead cam engines.
The lifter faces are domed in the middle (on a flat tappet cam) and the cam lobes are also not cut square across the lobe. They’re actually a tiny bit taller (.0005-.001) on one side of the lobe than they are the other (if they’re in good shape). This means the lobe, in theory, is only contacting one side of the lifter face since the face is domed. This causes the lifter to rotate and in turn the pushrod.
This could be one of those where do you stop things. If the lifters are badly dished then the cam lobes should be carefully inspected (although it would be impossible to mike them) and if one needs a cam replacement then that means a timing chain set also.
If the vehicle runs a tad rough or a bit weak then maybe it would be best to perform a compression test, possibly a valve job and get everything at once.
That’s the bad thing about engine internals; one thing always leads to another it seems.
I know, I was just keeping you honest on that lifter rotation through the rocker arm thing. I’d expect the keepers to totally eliminate any valve rotation, certainly the lifter would have little to do with it. Possibly some effect from rocker arm geometry, or the design of the face pushing on the valve.
As I understand the whole lifter rotation thing it was to help minimize wear on the camshaft, lifter and rocker arm.
Just couldn’t resist yanking your chain. No harm meant.
I had this on a Ford one time. Some of the studs were notched half through. I put in new studs and with in a couple of weeks, the new ones were notched just as bad as the old ones. I did this at 61k miles. I didn’t do it a second time and the car went 212k miles before getting wrecked.
Unlike JayWB, I didn’t know that. Thanks for the explanation.