[grivera]

Originally Posted by Formulajones

It's all pretty easy to explain. In Tuscon you're at about 2500 feet elevation. The higher up we go here, the more these engines can use timing. On the dyno the initial setting doesn't matter much because we are just looking for total timing where the engine makes best power. Vacuum advance isn't even used, and idle quality isn't that much of a concern and quite frankly while on the dyno the engine doesn't spend that much time idling anyway in most cases.

So you get the engine back, now you're near sea level, things are going to change a bit. Total timing where the engine made best power will probably be the same but how fast it comes in as well as where you put initial timing is likely going to change a bit when this engine is put in service. Toss in the fact you should also be running a vacuum advance unit, which also isn't used on the dyno, and it's a fairly good bet the engine simply may not want that much initial timing or vacuum advance added. The noise is dead nuts on the same thing I hear here with too much idle timing. It's only ever occurred idling and pretty much goes away with RPM, just as in your case, and never had any detrimental affects with this happening other than it can be annoying to some.

The noise the previous instance also makes sense and several of us have discussed this recently. With the bushing in the distributor eating itself, that shaft is moving all over the place. There is no way it can control timing doing that, so the timing is just everywhere and most likely over advanced in all conditions. Which explains why the rings had moly flaking off, that's typical of an engine with too much timing and detonation while under a load. That was just a fluke instance of an MSD part failure that isn't common, but things happen. Now the noise is back and exactly the same. Not because of a bad distributor bushing, but because there is likely too much idle timing setup in that distributor.. It's easy enough to change around and experiment with. The nice thing about those MSD's is they come complete with a timing chart and various bushings that bolt into the breaker plate to set the initial and total curves where you want them, and I've found those charts to be pretty darn close to accurate. 5 minute fix. If you're running vacuum advance, leave that unplugged for now until that part is dialed in, then slowly bring in some vacuum advance later.

Good troubleshooting advice! Do you by any chance have a video of the scenario you describe- an engine making noise at idle with timing too advanced?