After the June 6th ET race, the Camaro seemed to be missing a little. I tried changing the plugs (had some Bosch plugs laying around), #2 seemed a little wetter than the rest; helped a little but didn't completely go away. After the racing last Friday night, the miss was very pronounced Saturday morning (didn't really notice it on the way home Friday night). Pulling plugs, #2 didn't appear to be firing, and #8 was "worse" looking than the others. So, Sunday afternoon did a complete plug/wire/cap/rotor tune-up, didn't make any difference (even though the cap & rotor were starting to look nasty). I put the compression gage on #2 for a quickie test, just started up the engine with the gage hooked up (abnormal test, to be sure), it had 60 psi at idle, 130 when I rev'd it up a little. Since I'd never done it that way before, I wasn't sure what to expect.

So, last evening I finally pulled a valve cover to see if anything shouted at me - it did, #2 exhaust spring was broken one coil from both top & bottom. I've never broken a valve spring before, but the good news is the valve didn't drop, and when I put air pressure on the cylinder, both valves sealed good & tight (the total cylinder leakage was much less than the 396, for instance).

Since I put it together in 2005, the valve stem seals haven't been all that "pure", so I'll be looking into that as well. The shop put positive spring seals on the intake and hard umbrellas on the exhaust, perhaps we'll change that.

Not looking forward to the job, #2 is the easiest cylinder (#1 close behind) to get the air adapter to with the headers, I'll probably just drop the headers to make access easier. But, hopefully it'll be back together soon. I'm going to be out of town a lot in the next couple of weeks, today and tomorrow are the only real chances I have to work on it. Next race is the 18th.

 

You probably already know this (but i'll dare say it anyway), i've removed valve springs with heads on the engine, simply by bringing that cyl to TDC. The valve can only go down maybe 1/2" at that point before bottoming on the piston. I give it a whack with a socket and hammer to break it loose (before bringing it to TDC), then use the "claw" style spring compressor. Works for me, rather than the air setup.

 

Yeah, and I've seen it done, but on higher compression engines (and not SBC).

The air method has the added benefit of providing an engine sealing test while you're at it. Plus you don't have to worry about being able to compress the spring enough to get the keepers out.

I've got a stud-mounted spring compressor from Summit that I used for the first time - makes me wish I'd had it years ago.

 

Got all of the springs replaced tonight. No other apparently distressed springs, although you can't really tell that without a spring tester (which I don't have). The valve stem seals were pretty hard, apparently from an overheating incident a couple of months after the engine was put together - the synthetic oil probably saved the engine, but the seals got cooked. No significant leakage while the cylinders were pressurized, nothing coming out of the cooling system. I used positive stem seals on both intake and exhaust, as well as using the factory o-ring - better not use oil now.

There was a surprise on the driver's side head. I took pictures, but don't have the adapter to download them. I won't spoil the surprise, suffice it to say it's something else I've never had happen to me.

The headers came out without having to lift the engine, passenger side from the top, the driver's side practically fell out (wouldn't be able to lift it out because of brake lines going to the line lock in the way). I do have poly engine mounts, that probably helps. People keep asking about ease of installation, now I can say I did it with the engine in the car (attached them to the engine and then installed the engine the two previous times).

Tomorrow I need to put it all back together. Had to remove the AC compressor and PS pump to get the driver's side header off.

After all this, the car should run REALLY well!

 

First, a picture of the broken spring.

 

Now, what I didn't expect to see (and haven't seen before, nor heard of before).

Any Sesame Street alums here? "One of these things is not like the other." Can you tell which one?

Each nut unscrewed in what seemed like a normal fashion. However, one nut looked like it had some oil across the hole when I pulled the rocker out, further examination reveled it wasn't oil. Then, when I went to put the spring compressor on the #1 exhaust stud, it broke off in a similar fashion.

If someone can explain this, I'm all ears.

(Sorry for the poor quality of pictures - camera phone.)

 

? I can't tell what i'm looking at there?
You removed the rocker arm nut (poly lock?) and there was something that looked like oil? What do you mean oil across the hole? Which hole?
The #1 exhaust rocker stud broke ?
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Is there wear on the sides of the threaded stud? Or did it seem to just crack out of nowhere?
Which studs are those? ARP?
Which nuts?

 

As in a film of oil across the hole of the rocker arm nut. Turns out it was the end of the stud still inside the nut.

#1 and #5 cylinders had one stud each broken in such a fashion. Approximately the part that would stick out of the top of the nut when the rocker is adjusted. The fracture surface on #5 was obviously smeared from running after cracking, but the #1 was almost a clean fracture surface. Final fracture was a small "ring" around the outside of the stud (going back to my old failure analysis work of days gone by).

Maybe I can get some better pictures this afternoon.

 

Well if those are ARP studs, and non-poly locks (typical all metal lock nuts) that might be your problem there.
ARP says that lock nuts crack their studs. I think Evilcartman ran into this a few years ago. (or another guy with a white camaro and a 350 who runs 11's or 12's...)

Is that the case?

 

Just standard screw-in studs. I got the heads from Competition Products, bare with "head completion kit", back in 2001. The heads had a set of studs, and the "completion kit" had a set of studs, neither CP nor WP claims the studs are ARP's.

But, yes, standard lock nuts.

{edit}Wait, the WP instruction sheet says "ARP studs 134-4001". Perhaps I got the WP studs on one head, and CP studs on the other. I'll have to look more closely now.

 

Hmm indeed eh? standard lock nuts and ARP studs apparently don't play well together.
Might end up having to replace all of your studs, and nuts

 

Both heads' studs were the same thing. Compared them to the other two sets I have (did I mention I've done the CP/WP head thing twice?), all three were different, but no markings on any of them. I chose the set that looked the most different (as if that means anything), and replaced them all.

 

Here are a couple of pictures of the broken studs. Looking at the fracture surface more carefully, they are not smeared, but clearly fatigue. Started at the thread root, worked its way across the bolt. Classic fatigue failure.

 

Hmm, root cause? What rockers? THink the slot isn't long enough? Or...?

 

They are long-slot roller tip Elgins. I checked them over very carefully, there was no evidence of contact in the slots.

It may have something to do with ARP not wanting you to use regular self-locking nuts on their studs. That's about where the top of the nut would be. Why it would happen, how it would be loaded, is a bit of a mystery, except the interference threads would take most of the load.

Remember they weren't broken off when I started taking the rockers off. One of them backed out past the threads before it broke off in the nut, and the other nut came off completely and the piece didn't break off until I started screwing the spring compressor on it.

 

I have to agree with Sonix on this one. I've also read that you're not supposed to use the standard, stock style rocker nuts with ARP studs. My guess is the out-of-round shape of the stock nuts probably causes them to cut into the threads of the stud ever so slightly, which could cause a weak spot. Yours is the first post I've seen with actual proof of this phenomenon, but I have read many times that poly-lock style nuts are required for screw-in studs. I guess it's a lucky thing that they didn't break until you were taking things apart, instead of at a high rpm! I'm replacing the ARP's on my AFR's with longer ones, and I tried screwing a stock nut on one of the old studs, and it actually took quite a bit of torque to get the nut to start screwing down on the threads, so I can see where it can easily damage the threads on the stud. The reason I was screwing a stock nut on there was that I was using a lever style valve spring compressor to remove the keepers/valve springs, and I figured it wouldn't matter if I used an old nut on the studs since they're getting chucked in the trash anyways.

 

Where are the rockers riding on that stud? The wear mark on the shoulder looks quite high. If the rocker ball or rocker shaft (depending on which you used) was riding mostly on the thread portion, you invited that failure to come play.
I'd say some pushrod checking is in order, among other things.

What brand valve springs? Any idea?