Rocker arm lock nut backed off???

Fired up my new engine today and while warming it up and seating the rings, after running about 8 minutes (water temp about 165*), it started to sound noisy, like valve adj loose, oil press good, brought RPMs up to about 2500, and it popped back through the carb. I thought it may have closed up a plug, but pulled Valve cover, the #5 ex rocker adj screw lock nut had backed off and fell onto the head, push rod eat up the alum rocker arm. What the He**??!!
After I set the valve lash cold, I went over the nuts with a torque wrench, so I know it was tight. But to loosen and fall off after only running for just a few minutes, it would seem that it was left loose.
Anyone got any other sugestions? Why would a nut loosen? All the rest were tight.
Anyone know where to buy 1 MP alum roller rocker arm??

Thanks guys, Brian Dunnigan

you might want to look at the lifter on that lobe before you go any farther.don't ask how i know this,but it was expensive.

I had some adjuster screws on my Crane rockers that were not the proper hardness and they would let the rotating pushrod get a bite on them and rotate the adjuster out. Pushrod length can also be an issue. If you're even 1/16" out on the length, the oil will not squirt directly on to the cup at the top of the pushrod, leading to the same problem.

http://cgi.ebay.com/ebaymotors/Mopar-Sma...sQ5fAccessories

it says w2/w5 exhaust..but it is the same rocker as the standard heads take intake or exhaust.

What procedure did you use to set the valves? What are the specs. on the cam at .050 and lobe seperation angle?

Cab,
The cam is a MP .590 solid that I had in my other engine. The cam, lifters and push rods are the only internal parts that are out of the other engine. Different stock 440 block & crank, Stealth heads, Ross pistons and Ohio Crankshaft rods.
I really need to find an explanation for this before I just feed it some more parts.
I adjusted the valves using the old Direct Connection chart (sticker on firewall). The cam card calls for .028" intake & .032" exhaust. I actually set them at .026" and .030" cold and was warming the engine to rest them hot.
I'm amazed that it back completely off in that short of time, even if it was left loose.
I'm a Diesel truck mechanic (we're "techs" now) and we had 25 2000 model Macks that would be fine, sometime for 50K miles, no one touched them, then would back off a adj screw lock nut, kick the push rod out and sound like it had "blown up". Always exhaust. Mack couldn't tell us why.

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it says w2/w5 exhaust..but it is the same rocker as the standard heads take intake or exhaust.

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I have big block engine.