I recently rebuilt the L98 engine in my Camaro, and I'm trying to get it running correctly. Unfortunately, I keep snapping the same rocker arm stud -- cylinder 5, exhaust. This is GM's 3/8" screw-in stud, p/n 12552126.

When I was breaking in the engine, the aforementioned stud broke. I adjusted all of the valves with the engine off, using the "intake closing, exhaust opening" method. My machinist and I attributed the stud failure to GM's quality control, and I bought a new one.

After I got the engine running reasonably, I adjusted the valves again with the engine running. All was well.

I ran the engine a little more to tune the idle and set up some other things. Thus far, I haven't surpassed 2000 RPM. I haven't even had a chance to drive it, yet. I was letting the car warm up today when the stud broke for the second time. I think it was at 1000 RPM or less. The pushrod didn't bend in either case.

I don't understand why this stud keeps breaking, and I doubt it's a quality control issue. I am running a ZZ4 cam (0.474/0.510) in a roller block. The heads have been machined for larger springs (ZZ4 style) and the valve guides have been cut to accommodate the extra lift. I have longer pushrods (7.270" vs. 7.194"), too. I've retained the factory 1.5 stamped steel rockers.

My machinist isn't sure as to why this is happening, either. He told me to check the alignment of the stud in relation to the other ones, and to ensure that the valve isn't bottoming out on the guide. He also said that it may be due to coil bind of the spring, and that I should check the clearance between each coil at full lift.

When I put the motor together, everything checked out correctly -- there was no binding and visually, everything looked fine. I am noticing a slight miss at idle, however, and it may be linked to this breaking stud. I've attached a few pictures.

 

One thing I noticed is that you have no guideplates and you are not using self-aligning rocker arms so what is there keeping the rocker arms centered on the valves? Maybe the rockers are sliding to the side and side loading which is causing it to break. Maybe a matter of time before they all do this.

 

That's true; I forgot to mention that I'm not using guideplates. The studs are designed to not require the plates, but I didn't realize that non-self-aligning rockers may need them with this much lift.

I also want to add that I (mistakenly) used red Loctite on the studs. My machinist said that the Loctite isn't properly sealing and might cause the hardened studs to break when they contact the coolant. Upon removing the broken stud, coolant began to pour from the hole (water jacket). The studs were also incredibly hot right after they broke; I couldn't even pick them up. The engine never did reach full operating temperature, either.

Here is a picture showing the coil compression. Should the top two rungs of the spring touch each other?

 

The studs being hot is just a result of using stock type rocker arms.I even had a set of comp magnum rockers on with slotted ball fulcrums and i started my engine for a second just to move my truck 30 feet and when I pulled the covers to chang emy rockers to full rollers, the ball fulcrums were so hot i couldn't even touch them. Once i put the roller rockers on they stayed cool.

BTW: What heads do you have? Stock Iron L98's? What do the pushrod holes in the heads look like? Are they a big round hole, open or narrow slot?

Why do you have longer pushros than stock if it is just a rebuild? Longer valve stems?

EDIT: I don't think any of the spring coils should be touching. there should be .060 clearance minimum at maximum lift. What ZZ4 springs? What installed height?

 

The push rod holes in the head are a narrow slot; they're factory L98 heads that have been modified for the increased lift of the ZZ4 cam. I didn't feel that guide plates were necessary, so I didn't have the push rod holes enlarged.

The springs are the ones used on GM's ZZ4 crate motor. They're slighly larger than typical SBC springs. Installed height is 1.78", and they were shimmed to match that specification.

I took the broken parts to my machinist, and he noted a large gash in the stud that snapped. The slot in the rocker is also heavily worn. By looking at the contact patch on the valve, he is pretty sure that this all happened due to incorrect push rods. I installed longer push rods since the new cam's lift is much higher than the factory L98 cam lift. However, I didn't take into account the fact that the block and heads were decked... in essence, I did the "right thing" but the extra details caught up with me. I intend to check the push rod length with an adjustable push rod. The stock size might even work.

Take a look at the first picture and note the contact patch on the valve -- it's not centered. Interestingly, a few of the other valves seemed to have a decent contact patch... but they're still rubbing on the stud. Maybe the slot isn't long enough?

A few of the rocker arms appear to have cracks around the slots, so I'm in the market for new rockers, as well. I would prefer to stick with the stamped steel rocker because they're less expensive, but I'm thinking I might need another style. Is there any way to check the valvetrain geometry to determine exactly what I'll need?

In regard to the guide plate issue: I have spare SBC valvetrain parts, and I was comparing those rockers to the ones on my Camaro. The slot in the arm is a lot wider than on the spare; this does indicate side-to-side movement of the rocker. Also note the contact patch on the valve is a line, whereas it's a dot on the spare valves that I have. Is this unusual?

I know the long posts can get annoying, but there's a lot of questions -- and maybe a lot of underlying problems -- in regard to this stud breaking.

 

What gave you that idea?

Here's my take. You used longer pushrods. Now the springs hit coil bind before the the lobe is at peak lift. The pushrod wanted to go up further, couldn't, broke the stud. The pushrod length doesnt change just becuse you increase cam lift. The ZZ4 cam may have the same lift, but the heel of the cams lobes are the same as the L98, or close enough at least.

 

I read one of the posts in regard to longer push rods and the ZZ4 cam. I based my choice on the contact patch that the push rod made on the valve -- with the stock push rods, it didn't look completely centered. But, I could have been looking at it entirely wrong.

I checked the springs at full lift, and there was a fair amount of clearance between each wire. Granted, the lifters weren't pumped up... could that affect the measurement by very much?

 

Get a pushrod length tool and recheck youre geometry. I don't think the ZZ4 is too radical that the difference in pushrod length, if any, would be too great.

What length did you get?

 

as a rule .1 more lift would require a .1 more push rod, untill you reach .1 more lift leave the length alone, actually you should check it so you know what you have and need. my guess is a problem in the way the rocker locates or a mixing of locating methods.

 

I spoke to my machinist again, who called several sources to shed some more light on this problem. Though he still believes that the push rods are too long, he thinks the main reason for the stud failure was due to the rocker arms.

1987 was a transitional year for the small-block Chevy engine in the F-body, moving to a roller camshaft, centerbolt valve covers, etc. One of the changes was moving to self-aligning rocker arms. For whatever reason, my Camaro ('87 Trans Am engine) had non-SA rocker arms and NO guideplates. This was probably due to a moronic previous owner, or an early run of '87 engines. I have no history of this engine, other than it came out of a 1987 Firebird Trans Am.

Upon my swapping cams and modifying the heads, there was probably too much lateral play in the rockers, which eventually cut into the stud and broke it apart, as GASGZLR originally described.

My machinist suggested that I get SA-style rockers with longer slots. The narrower slot, he believed, is what was causing the stud to break. However, nobody makes that in the cheaper stamped style. Crane Cams and Comp Cams are willing to sell me their high-performance roller versions, ranging from $200 to $300 -- more than I'd like to spend, but I'll do it if I have to.

Since I'm basically running a ZZ4 valvetrain (cam, springs, retainers, studs), I checked into the rocker arms that the crate motor uses. It's GM p/n 10089648 (12495490 kit), self-aligning style. I doubt they have longer slots. I can get them for $52.08 through GMPartsDirect. This is the rocker that I'd like to buy.

This choice all boils down to the rocker-oriented reason for the stud breaking -- is it due to side-to-side movement (requiring SA rockers), or due to front-to-back movement (requiring longer slots)? I checked the slot length and width against a factory SA rocker that I have ('88 350, Chevy Van), and the length is exactly the same. Width differs anywhere from 0.010" to 0.020", indicating that it's the side-to-side movement that caused the premature failure of the stud.

That's my conclusion. Being that GM uses their stamped SA rocker on the ZZ4, I'm probably safe to use it on my engine... or so I think. Does this premise sound logical, based upon my observations?

The longer pushrods that I used may have aggravated the situation, too, by overextending the rocker throughout its range of travel. Whether that had anything to do with the stud breaking will remain to be seen; my adjustable push rod is in the mail .

 

Your 1st picture tells the whole story. The stud shows bending overload fracture characteristics, no side-to-side influence or fatigue whatsoever.

You need long slot rockers. The one from the failed stud appears to be cracked.

Choose the pushrod length to get proper stem contact. The valve stem tip for the failed stud doesn't look too healthy.

 

I'm kinda with Stekman on this, I think the longer pushrods are forcing the rocker against the stud. It doesn't take much, (I think ) Comp cams recomends checking the pushrod clearance on 1.6 rockers, even on stock applications for this reason: sometimes the manufacturing clearances line up to create a problem area. If you had a different rocker, you may not have had a problem, if you had a different pushrod, same deal. It just may be that you had a couple of parts that happened to be together that caused the problem. Change out the pushrods and the stud and/or the rocker and the problem may go away. I would say that you're fortunate in that this was your only problem.

 

It's not the legth of the push rods. Longer push rods simply make the rocker nut adjust to a different place.

I see several things, looking at those pics:

1. You have the wrong retainers for the springs. Looks to me like you have 1.45" springs and retainers for 1.25" springs. That's not what's breaking studs; but will eventually cause other problems.

2. The rocker arm is damaged at the push rod end. That may be a symptom, not the problem however.

3. Notice the difference in the appearance of the exposed part of the valve in the rectangles. Looks like 2 completely different valves. I'm guessing the one with the extra height there is the one that fails? If so, it's because that spring probably has about .125" less installed height than the others, and is coil binding. If you didn't check that one, it may be binding even though whichever other one(s) you checked were OK.

4. Looks like the valve end of the rocker slot has been hitting the stud. The end of the slot looks polished. That'll take out studs in a hurry.

In short, it looks like you have a hodge-podge of mis-matched parts, and whoever set the heads up wasn't very careful about it.

 

Now that you mention it, the pic would be a good idea.

 

I took another look at the grooves that were etched into the broken stud. It was on the spring-side of the head, indicating that at full lift the rocker was rubbing the stud. Now, looking at the angle that the stud broke, I can see how it snapped... and the direction that it snapped. I have problems seeing the obvious sometimes .

I still don't know why my set of '88 swirl-port heads used both the narrow push rod slot and SA rockers... . And, I wonder why the contact patch on the tip of my valve is rectangular, not circular. I've read every thread there is about SA rockers, and contrary to what's recommended, many people find that GM used SA rockers with the narrow guide holes. I'm beginning to wonder if I shouldn't do the same thing. But, again, nobody makes an inexpensive self-aligning long-slotted rocker. Any advice here?

 

RB83L69, thanks for your reply. The springs are the ZZ4 style, 1.32" OD with an installed height of 1.78". The retainers are GM p/n 12556463, which is the same style used on the ZZ4 crate engine and LT4 engine. This picture isn't very good, but it shows what the retainers look like on an LT4:



Yes, the rocker arm is in pretty bad shape. I'm not sure if it was like that before I got the heads reworked or not; I sent them to the shop assembled.

I'm going to take a closer look at the clearance between the top of the valve stem and the retainer to see if any other valves are messed up. The frontal picture was taken when the motor was out before it was run. It's actually showing cylinder #1.

 

RB, I checked the valves in the location that you had squared in your picture. The valves with the extra height at the top are exhaust valves. Though that measurement is different between intake and exhaust valves, it's the same across intake and exhaust valves. The height of the springs appear equal, so it's probably due to the way the spring seat was machined or the way the valves were manufactured.

I found a better picture of the retainers; they're also used in GM's LT4 Hot Cam kit. I guess they don't seat on the full surface of the spring.

 

Well, look at it this way, you'll never, ever make this mistake again.

 

Here is something that is the reason i stick with GM parts: They are frm the factory so there is no need to get custom parts made most of the time. I have the LT4 hot cam which is more radical than the ZZ4 cam, and it uses the stock pushrods.the only reasons I can think of for changing the pushrod length is longer valve stems, smaller base circle cam(non of GM's), or extreme milling of both the block and head.

RB, changing the length of the pushrod does change where the nut will adjust at but it also moves the rocker to a 90 degree angle to the stud (or more)when the valve is closed. This should only happen when the valve is at half total lift. The rocker should be lower on the pushrod side when the valve is closed, not equal. the longer pusrod will make the rocker try to move too far to open the valve, and bind it. Especially with stock slot rockers.

You want it like pic 1 when the valves are closed. NOT like pic 2 with closed valves. This seems to be what blue86iroc setup is like when closed(2)

 

I received my new rockers today. I opted for the Comp Magnum roller tip rockers. Since I have the narrow pushrod slots in the heads, I did not get self-aligning rockers.



I test-fit the factory pushrods with the new rockers and observed the rocker geometry and the contact patch it made on the valve stem. At no lift, the center of the roller is slightly towards the intake manifold-side of stem center. No lift:



At half lift, the roller is pretty much on the center of the valve stem. The rocker is close to 90 degrees to the stud. Half lift:



At full lift, the roller is just slightly to the exhaust manifold-side of the valve stem. Full lift:



The contact patch that the factory pushrods (with the new rockers) make is very similar to the patch made with the longer pushrods and factory rockers. You would think that the longer pushrods would push the contact point out further towards the exhaust manifolds... I think this demonstrates the binding due to the short slot on the factory rockers.

After I tested the original pushrods, I decided to use an adjustable pushrod to idealize the situation. In setting up pretty decent geometry, the "ideal" pushrod came to about 0.020" to 0.030" shorter than the factory pushrods. Taking into consideration the collapsable nature of hydraulic lifters, this equates to about factory pushrod length, or slightly longer.

I think I'm in the green now . I appreciate all of the help, guys.

 

RB, it looks like the stem heights are the same, but looks like the groove location or those damn .050 offset keepers have the retainer lower in the pic

 

I thought with the narrow slots in the head and no guide plates you NEED self aligning rockers. I have the narrow slots for the pushrods and my engine has SA's stock.

If you dont have guideplates then you need Self Aligning rockers.

Or I could be wrong -- someone correct me.

 

88305tpiT/A, you aren't supposed to have self-aligning rockers with the narrow pushrod slots in the head. When I was searching for the answer to that, RB83L69 posted this:

From what I found, GM mixed narrow head slots with self-aligning rockers on quite a few engines. I have a set of L03 heads from a Chevy Van (1988) that has both systems. However, the aligning part of the factory SA rockers appears to be pretty sloppy... so I doubt it'd ever bind in a factory application. Another set of heads that I have (882) from the mid-1970s has narrow slots, and this was before GM used SA rockers on factory heads. My '87 L98 was the same way.

 

Notice the slots in the rockers...that is your whole problem.
When you used longer push rods you used up some of the slot then when the valve lifted, the slot went against the stud and could move no more, so it broke the stud. I'm sure it bent it first, then broke. You should be fine now with the longer slots. But be sure to check and see if the stock length push rods are the right length (they should be ....the ZZ4 cam has a normal base circle).

 

:hail: stock pushrods.

 

I had same problem. Rocker slot wasn't long enough, binded and snapped a stud. Unfortunately, I had the push-in studs, and I broke all the threads off I did however get a good deal on a used set of Sportsman IIs. I also went with the Comp Cams Magnum roller-tipped rockers, but I bought the self-aligning ones.