I have a rebuilt 302 on a 77 F100. Set the valves correctly. #1 TDC, adjusted to zero lash plus a turn. Started....ran great for a minute then a a rattle started then went to a clanking. Tore it back down and the rockers were way off. Put new lifters back in again reset again with same procedure then rechecked at each valves lowest points. Put it all back together started first try. Attempted to break in. Ran at correct rpms for about 15 minutes....tapping started again....then the clanking again. Rockers so loose I can almost remove the push rods! What is going on? Not HO parts. Standard everything. Do my rocker nuts need to be replaced? What could be causing this?

 

You are using the wrong valve adjustment procedure. Set at TDC and torque the rocker nut to 20 ft. lb.

 

Do the lifters need to be dry or primed? Also...do the rocker nuts need to be locking nuts? I've done the procedure I did this time on HO 302, 351, 350 Chevrolet. A number of times and have never had this happen before. I've heard of the 20 ft. Lb. thing by I thought that was on the old y engines or solid lifters

 

Are you using the proper break in oil with zinc additive? If not it's possible you have wiped the cam lobes. Does not take long to ruin a flat tappet cam. One rocker coming loose could be a rocker arm stud pulling loose, but unlikely all of them.

 

I am using break in oil with Zinc

 

New Hydraulic lifters should always be pre-filled. Best way I have found is to fill a coffee can with oil, set a lifter in it and then use an old pushrod chucked up in a drill press to "pump" oil into the lifter with the up and down motion of the drill press. Of course you do not have the drill press running! It is possible that you have screwed the cam up as well. Do the rocker arm nuts feel like they are locking or do they spin freely all the way down?

 

I prefilled the lifters the first time and just soaked them the second time. Engine actually ran longer the second time before everything came loose. If the can was screwed up it would have ran horrible from the beginning on the second attempt, I would think. The rocker arm nuts can be run down to zero lash by hand.

 

You shouldn't be able to turn the nuts down by hand they are supposed to be lock nuts, that's what keeps them adjusted. I thought those were supposed to be positive stop rocker arms in 77, are they older heads?

 

They are the original heads. I will get new lock nuts. Which is the right way to set the lash? The 20 ft lb way or the the way I did it?

 

You can use either way, I have done it both ways and had good results

 

Thanks for all the help. I ordered new factory correct nuts (not locking by the way) but they did get tighter at the final twist. I then added a lock nut and ran them down like a jam nut and put a little thread lock on there for added assurance. They will never move again! Started right up and runs amazingly!