So I am still breaking in a freshly rebuilt 460. Being my first carb'd pushrod american V8 experience I don't have a whole lot of reference of what are normal noises and what is not. Well I know what is NOT normal. I pulled the motor to rebuild it due to a broken piston skirt. That knock became so loud you could hear it down the street.



Now that I have a well balanced, and mostly exhaust leak free motor I am listening close for any abnormal noise. I can hear a light knocking noise at idle or when i am moving and holding a extremely light throttle (slowing down but throttle is cracked slightly). I have read that a cracked flex plate can cause this and I honestly didn't really take too much of a look at it when i put it back on. Also it could be fuel pump, valve train, or wrist pin knock. As for volume, I would rate is as about 2-4x quieter than the turn signal relay. You REALLY have to listen for it. It feels great power wise and sounds good when you rev it.

Am I being too picky? I feel that if I had a more muscle car like exhaust or any sound deadening I wouldn't hear a thing. I also only have about 2 hours on the motor and it is still on the break in oil which is a little on the thin side as far as viscosity goes. Pressure is good, timing is right. I did have to richen it up a little as it was running a bit lean and I have done 2 rounds of header bolt torquing.

 

My guess is that this;
is causing this.
A light knock like you describe is often the connecting rod if it's a rather low tone, rather like a knuckle on a solid piece of wood.

How "thin" is this oil?

I suggest you change it and see what you got. But listen carefully for it getting worse.

 

I'm using a 10w30 mineral break in oil. It's as thin as I would run in this motor. I am planning on changing out to a 5w40 synthetic. On the old motor due to age milage and condition I was running a cheap 15w40.