Ok so I'm working on a 1987 Calais and I'm seeing something I have never seen before.

The car had a blown head gasket and a cracked head so put a re-manufactured head on it that we had to order and got it started. (BTW the torque values for the rocker arms in the Haynes manual are completely wrong...they stick all the valves open with ZERO compression) Anyways, as I'm adjusting the rocker arms with the engine running, I watch cylinder 3 exhaust rocker arm nut work itself back out. It chatters and clatters until I tighten it back down, then I watch it work itself back out. Anybody have any suggestions beyond lock tight.

My apologies...I forgot to put the engine type. it is a 2.5l tech4 FWD...distributor less, hydraulic roller lifters...supposedly you were supposed to be able to torque the rocker bolts down and forget about them but as stated above...that is a no go.

Red Loctite

As far as I remember, on the 2.5, you just torqued it to spec....the 2.8, I think, was a whole different ball game.....

Do as Mike suggested.......but don't torque with engine running......

Also, hope you got a good valve cover gasket(Best one'* were rubber with a metal ring at the bolt holes).......they were prone to leaking......also make sure the flange on the cover is flat......main thing is to not overtighten and deform the flange....