Rocker arm came off '96 LT4 Grand Sport Corvette

[mcox8051]

The other day I took my Corvette for a spin and all was well for about 25 miles. Car runs great and quick and I never tached it over 4500 rpm, I don't drive hard, just cruise around. Started hearing a ticking, like a lifter or something, it started running rough, limped home, popped the hood and saw a valve cover bolt moving on the right side! I knew this was not good. Removed the cover. The rocker arm on number 6 cylinder was off the exhaust valve and had broken off the spacer for the valve cover bolt. I was able to remove the broken threads. The rocker is damaged. The two keys were laying in the head. Other than the damage to the roller rocker, everything is straight, pushrod and stud. The rocker arm nut was tight (maybe because it was jammed? I wish I would have put a straight edge across all nuts before removal but I didn't) I was wondering if anyone knows what might have happened and what I should do. The previous owner put in "a GM Hot cam, upgraded springs, new lifters, new valve seals." He won't return my messages for part numbers. Something had to cause this to happen. Removed the intake and I'm going to replace that lifter, in case it collapsed. These are the original roller rocker arms on the car, found a new one on eBay. My car has the newer style and was not involved in the rocker arm recall. It looks to me like the keys came loose somehow on the valve spring. Is it possible the "upgraded" springs are too stiff or strong for the stock keys? I have also ordered new GM retainers, keepers, and springs and plan on replacing all 16. It was suggested I do a cylinder leak text. I did, cold engine, 9% loss. Checked number 4, same thing, so I don't think the valve is bent. I did one other check, piston at top, dial indicator on the end of valve, pushed down until it hit piston, checked by turning all the way around, it shows .011 runout. Don't know how precise this is.. Car has 69k miles. The previous owner had just installed the cam and put less than 500 miles on it. I drove it home from Texas 1000 miles without any issues (other than power steering pump failure, but thats another story!), hit 111 mph at one point. It runs beautifully, at least until this happened. I have read where the rockers are non-adjustable, torque to 18 lbs and go. Is this correct?
Any help very appreciated.

[c4c5specialist]

HI there,

Those are not GM OEM rocker arms.

They were not installed correctly and backed off.

That is how the damage occurred.

I would be checked EACH INDIVIDUAL rocker and EVERYTHING ELSE before you proceed further.

Allthebest, c4c5

[mcox8051]

Originally Posted by c4c5specialist

HI there,

Those are not GM OEM rocker arms.

They were not installed correctly and backed off.

That is how the damage occurred.

I would be checked EACH INDIVIDUAL rocker and EVERYTHING ELSE before you proceed further.

Allthebest, c4c5

They are original OEM part no. 12557779 for the LT4, made by Crane for GM. Ok, so the nut backed off. What is the procedure for tightening. Do you use Locktite?

[c4c5specialist]

No, they are not.

No Generation 2 small block rocker arm was EVER stamped with a Chevrolet bow tie, however the GM PERFORMANCE PARTS ROCKER ARM WAS and those are from the TSB 96-c-07a so they were changed.

The studs that you see in the valley were made to use a net lash nut torqued to 18 ft lbs.

No loctite is used.

Allthebest, c4c5

[mcox8051]

Originally Posted by c4c5specialist

No, they are not.

No Generation 2 small block rocker arm was EVER stamped with a Chevrolet bow tie, however the GM PERFORMANCE PARTS ROCKER ARM WAS and those are from the TSB 96-c-07a so they were changed.

The studs that you see in the valley were made to use a net lash nut torqued to 18 ft lbs.

No loctite is used.

Allthebest, c4c5

I got ya. I was told by the previous owner he changed lifters, I think the moron meant he changed the rocker arms. I've read where you just torque to 18 lbs, others say you have to follow a sequence: hub arrow at 12 o'clock number 1 cylinders' intake and exhaust valves closed (lifters fully down), tighten rocker nuts to 18 ft lbs on cylinders 1,3,4 and 8 exhaust valves and cylinders 1,2,5 and 7 intake valves. Then rotate the crankshaft clockwise one full revolution until the hub arrow is again at 12 o'clock and tighten rocker nuts to 18 ft lbs on 2,5,6 and 7 exhaust valves and 3,4,6 and 8 intake valves.......Is this the correct procedure? OR, don't the nuts just bottom out on the stud no matter where the rockers are? I'm confused. Thanks for the help!

[c4c5specialist]

HI there,

Below is the cut and paste directly from GM service information for these rockers.

7.4. For LT4 engines, tighten the valve rocker arm nuts.

Tighten
Tighten the valve rocker arm nuts to 25 N·m (18 lb ft).

LT1 engines are different and use the net lash type of rocker arm.
That is why there is a shoulder on the stud, so that you cannot go any further on the LT4, where as the LT1 uses a blind stud.

Allthebest, c4c5