naf

iTrader: (7)

84 Camaro with LG4 lost rocker stud for exhaust valve left bank while on interstate at around 65. Initial symptoms were an intermittent severe miss, followed by inability to hold an idle. Got her towed home, cleaned up the plugs and got her to idle, but with a severe surge. Heard the ticking under the valve cover...

History:

Re-ring/new bearings two years ago. Installed new valve springs (Z28 from Northern Auto Parts) lost the rotators and shimmed each to recommended install height. Used the Summit K1102 cam with supplied lifters. Set lash conservatively with engine running to 1/2 turn past tapping, rechecking each one. I recently did the first regular oil change (after swapping the breakin oil within a 100 or so miles) so maybe 3000+ miles? I'd have to check.

Any opinions on failure cause?

Damon

Nothing jumping out at me on that one. No tell-tale signs of running the rocker to the end of it's slot and binding, no overheating/lack of lube (doesn't look "blued" but it's always tough to tell from pictures) and no other collateral damage (bent pushrod, broken spring, bent valve) or you would surely have mentioned it.

Are these screw-in studs? Maybe just just got a bad one.

naf

iTrader: (7)

stock studs and the rocker was well oiled when removed, oil under the ball.

Top of valve tip looked good, no marks.

straight edge across the rockers showed all were even when the heads were assembled. The motor had 120K on it when it was refreshed.

I'll pull the intake next weekend, maybe failed lifter (who knows where the summit brand lifters come from). I'll have a better chance to examine the rest of the parts and confirm the valve is good, although it certainly appears to be fully seated now.

I hope to find something, because I don't want to fix it just to wait around for the next one to snap.

tom3

Sometimes crap just happens. Seems like a pushrod or lifter bottom would have failed before breaking off a solid 3/8 inch stud like that. Pulling that old stud out is going to be a bear I suspect. If the lifter looks ok, bad stud?

Damon

Hopefully you find the "smoking gun" on this one. Answers like "it's number was just up" rarely satisfy, but sometimes that's how it goes.

cardo0

Broken rocker studs is not uncommon. But after a recent overhaul the assembly becomes suspect.

Just noting i can see the stud sheared right at the ball/rocker fulcrum line. Also those ***** have no slots for oiling. One more thing is i hate the rocker/lifter adjustment by sound method. I just think its to subjective and inconsistent.

So for new rocker ***** i would recommend the slotted type.

For rockers i would check the clearance to the stud at full lift and when vlv shut. A thin paper clip unbent works good for this.

U can buy cheap tool that will pull out the old studs and align a drill to drill a hole for taping the same hole for a threaded stud.

For adj the vlvs/tappets u have to know, not just understand what the cam "base circle" is and know, not just understand what "zero lash" is.

-=Z28=-

iTrader: (3)

Boy i dont know... It sure looks like that ball was tight as hell in the rocker.. If your rocker geometry is wrong that will cause it too. Also high mileage OEM studs will break. What rpm was the engine at?

-=Z28=-

iTrader: (3)

how much lift is on that cam? How the springs were shimmed? Did the springs had enough coil clearance at maximum lift? Check the other studs for any signs of rocker contact. Any signs the rocker slot bottomed out on the stud?

mmadden55

-=Z28=-

iTrader: (3)

Like that guy. Makes quite a few videos. All of them are on point.

naf

iTrader: (7)

rocker failed during highway cruising at about 2000 rpm, steady state speed for 10-15 minutes before fail.

lift on that cam is a wimpy .421/.444 it's also got pretty lazy ramp rates, one of the reasons I picked it. I was looking for durability while keeping the flat tappet system with just a little more than the stock LG4 cam could provide.

upon removal I noted plenty of oil under the ball stud. the first thing I checked after looking for signs of clearance issues with the slot/stud.

This weekend I plan to pull the other rocker off and fire up the motor. ensure no other weird sounds emanate. then I'll pull the intake and examine the surfaces of all of the lifters (I will try to not get them mixed up). then the head comes off and I'll examine all of the other studs/rockers and straight edge the tops of the studs. pull out that valve and check for guide play and straightness.

any other suggestions are welcome.

naf

iTrader: (7)

head off and no discernible damage anywhere:

Elgin RV943X valve spring with damper, verified 1.125 at coil bind

Install height checked at 1.72 with .092 of shim under the spring

K1102 cam from Summit (found receipt)

Lifter looked good, as did intake lifter

pushrod straight.

straight edge across remaining studs showed all level.

will drop it by machine shop this week and get a more experienced opinion

anything else to check?

cardo0

Then it was either a defective part or the rocker was over adjusted until solid and it sheared the stud.

U have to know what "base circle" is not just understand. U have to know what "zero lash" is not just understand it.

DynoDave43

iTrader: (11)

Trying to learn something here...

Just watched this video. Very helpful. But...he says you must do this with the piston for the cylinder you are adjusting valves for at TDC (or the top of the compression stroke), NOT the exhaust stroke.

If the valves are closed (lifters on the base circle as seen at the lifter in the next photo), then what difference does it make?

Damon

TDC of the exhaust stroke both valves are still slightly open. It's the "overlap" period of the cam. That's why it's gotta be TDC of the compression stroke- both valves are at least 100* from opening in either direction.

Naf- I'm gonna go reaching for some really bizarre stuff here, just in case. I mean you never know. (Personally I think that stud had a crack in it already before the rebuild).

1102 is a mellow cam but it's still got more lift and more aggressive ramps than the peanut cam. Combined with upgraded valve springs that might have been more than an already compromised rocker stud could handle for very long.

You have that shim on the exhaust valves only, right? Assuming here that you just wanted to ditch the stock exhaust rotator/retainers with standard retainers. The ehxaust spring pockets are machined about 1/16" deeper than the intakes to make up for the added thickness of the rotator/retainers. A shim under the intakes would bring the spring installed height up way too short. Just mentioning to hear myself talk, really. I seriously doubt you would have made such a mistake (plus it was an exhaust that broke, not an intake).

When you measured spring installed height did you use a height mic (barrel style)? If so, remember they have a lower step where little 1.25" (stock) retainers sit. That lip sits about .150" below the top lip that is normally used to directly measure installed height. Makes the reading show .150" TALLER installed height than actual so you have to factor that out when you're measuring.

When you rebuilt the motor did you have the guides redone? If so, it's possible the exhaust guides are too tight. Won't notice it with cold parts but when they get hot the clearance can close to ZERO, grab the valve and things start breaking. Although I would admit you'll usually bend a pushrod before you snap a stud.

naf

iTrader: (7)

When the springs were replaced I installed shims under the exhaust springs, each required a 0.030 and a 0.060, as expected. I used a short piece of stock cut to 1.70 to check the height of each (intakes and exhausts) as I assembled.

The guides were not redone. All the exhaust guides showed the barely perceptible
'wiggle', which is still evident with the affected valve.

Onbusy

I had something similar to this happen about 8 years ago. I had just re-ringed the engine and changed all the bearings and sent the heads to a machine shop to be rebuilt. Long story short, the machine shop gave me back a different set of heads(TBI truck heads instead of the TPI Z28 heads I had), and the stock stamped rockers I sent with my heads to be hot tanked did not come back, they sent me back non-self aligning rockers, and as I was 17 at the time and didn't know any better I put it all back together. I snapped a stud, so I changed to some Comp Cam Magnum roller-tipped rockers in case I was bottoming out on the rocker slot and binding on the stud. Snapped another stud. Ended up having to goto a shorter pushrod, haven't had any problems since.

naf

iTrader: (7)

opinion of the shop is that the stud was cracked and eventually broke. he noted a black mark on the cross section of the piece of stud left in the head that made him think it had been cracked for a while before failure. he found no other issues.

promised the head back to me Monday. told him he was fine to keep it past Monday because once I pick it up I'm just going to have to start putting everything back together.

gasket set is sitting in the garage.

ASE doc

The valves aren't on base circle with the piston at the top of the exhaust stroke. That is in fact the overlap area of the cam and on larger cams the valves are both open together throughout that portion of rotation.

This guy's description is the old school TDC method that I used for years. It works but it's not the best way of doing it, especially with aggressive profiles. Comp Camps suggests the exhaust opening/ intake closing method, that accounts for lobe displacement angle and even the most severe ramp profiles. I have used this method on the last several engines I've setup. It IMHO is the most inclusive and accurate method. It's in their instructions for every one of their cams that I've done in the last few years. You can find the description of this method on Comp's website by simply looking up instructions for any of their cams.

I grew up with my dad, uncle, and grandpa adjusting valves with the engine running method. I still know old timers who stand by this as "the way it's done". I did it this way myself many times. I always thought it was messy and smokey. I've also opened engines up that had been adjusted this way, by old timers and myself too. I've found differences of as much as a full turn between valves that were adjusted this way. On a stock motor with a low top end power band, you may never know the difference. On a high test motor that makes power past 6K, it can make a huge difference.

Damon

I'm not even going to take a victory lap on this one. Just glad to hear it's going to be an easy fix getting ti up and running.