I just got my newly rebuilt 350 engine running, it took 6 months. After running it for 30 min to set the cam. I drove it around the parking lot. On my second pass the nut on one of my roller rockers came off, causing the exhaust valve on one of the cylinders to stay closed. We checked a couple others and they became loose as well. Is the problem that we didn't tighten them down properly, or could the problem be that the length of the pushrods might be too long?

 

Night rider,

I had this same problem. It was the nuts for the rocker studs. I used the old ones and should have gotten new ones. They would not stay tight. Check them first. Easy and cheap fix.