Just finished my 400 build up and it runs great except the valvetrain rattles so much it sounds like a diesel F-350.
The hydraulic roller lifters and roller rocker arms are Comp Cams, the heads are AFR and block is a 400.

I set the lash like a regular hydraulic lifter - take up the slack then go another half turn - is this noise normal, or did I do something wrong?

 

Try adjusting the valves with the engine running. You can get clips to go over the end of the rockers to keep oil from spraying everywhere, or, if you have a junk set of valve covers, cut the tops out, and use those for the adjustment.

A search will also reveal a goodly number of posts on the correct method of adjusting your valves on a non-running engine. I prefer the running method myself.

 

If the crank and rod bearings have larger than stock clearances and or if the top end oiling flow was restricted/limited by your engine builder, you'll need to run 20W50 oil to keep the lifters quiet at idle.
try it.

 

I increased the preload to from 1/2 turn to 1 full turn - no difference. Oil is 54 PSI at idle, my bearing clearances are at the minimum tolerance and side clearances are tight too.

A friend listened to it and said it is not valve tick - it sounds like more like a rock tumbler. Seems to be louder toward the front of the motor.
I pulled the belt and the noise persists, so that leaves the Fluidamper, or maybe the cam button banging against the timing chain cover.
No metal in the oil pan, so that's a plus.

 

Loose camshaft timing gear bolts. Happened to me.
Caught it in the nick of time before the whole thing was about to come unglued. Could have been ugly.

Gave my engine builder/machine shop a for not using a cambolt locking plate and locktite.

 

AS F-bird said. BTW, what rockers are you using?? Comps aluminum or the billit steel. I have the billit steel on my BBC Elky, with all the titanium in the valvetrain it makes noise. Billit and titanium don't expand like aluminum does, so it makes more noise. I would get a stethoscope, or a long screwdriver, and put it to your ear, up to the timing cover and see if you can hear the noise, likewise for the valvecovers.

 

I'll check that, thanks.
I have the aluminum rockers.

 

no prob, let us know how you make out.