406 Still Giving me a hard time.
 

So i replaced the collapsed lifters in my 406 SBC, and it is still making some noise. The best way I can describe it is a clatter at idle. Once I hit about 1200 rpms the noise lessens dramatically. I think that the valve train is adjusted properly. I'm wondering if I might have cam lobe or cam bearing problems. Anybody know how I can check the cam + bearings?

Fixx
 

roller rockers?

You have to rule everything out. Carefully inspect all moving parts including your valve springs. Are you certain you replaced all the lifters that were bad? Either check your valve lift with a dial indicator or measure the spring height at full lift on both your intake and exhaust. Document everything you do. It does kind of sound like a cam lobe but check everything out and go from there.

Good luck and keep up posted.

Thanks for the reply. FWIW I actually replaced all of the lifters. it almost sounds like the noise is coming from the back of the engine near the distributor.

I kind of figured you did. Distributor gear looks good??? It is a clatter and not a clunk right? Just wanted to rule out the rear main. What oil PSI at an idle?

yep the distributor gear looks good. Definitely more of a clatter than a clunk, but not tapping like you might hear under the valve covers. Really seems to be internal.

Mr Fixx - Standard stamped lifters.

silent choice? If so, check the flappers inside the y pipe. Exhaust pulses at idle will make them rattle

My oil pressure at idle is 40-45 psi. I don't think it's the exhaust flappers for a couple of reasons. I was working on it yesterday with the exhaust wide open most of the time, but more importantly the noise starts immediately when the starter turns over the engine, also all of the flappers were in perfect condition when I reassembled a couple of weeks ago.

The noise almost completely disappears once I hit about 1200 rpm. ?????

Do run a flex plate or a fly wheel?

fly wheel