For the last year or so, everytime i start the engine, and only when the engine is COLD, i have like a knocking sound, not rpm realated so much, like a rod knock would be, but more like a "tock, tock tock sound, say 2 per second. If i rev the motor slightly it goes away, its only at the low idle speed and ONLY when the motor is cold.
If i start the engine when the motor is warm, i dont have the noise.
I;ve checked the rockers, checked the converter bolts, and everything is good.
trying to figure out what the heck could be causing this? would a bearing do such a thing?
It seems odd it only happens on cold startup.
performs the same as it always has, doesnt smoke etc......
ANY IDEARS???

My 73 340 has been doing exactly the same for years. Goes away after a little oil pressure or oil splash.After higher comp. cyl. heads installed.I suspect piston slap, original factory pistons I believe.

Lifter bleed down. Not to worry about it, it won't hurt anything. More aggravating than damaging.

Mine would do that too if the engine sat for a few weeks without startup. I now turn the motor over for 5 seconds or so then stop, then pump the gas and hit the starter again with no noise.
It was worse when I used 15w-40 and 10w-30 oil. Now I use 5w-30 (full synth) + the 5 second prime and it no longer has the noise after a long period of no starts.

awesome to hear! had myself worried. i currently use 15/40 oil, but not gonna go lighter as i learned years ago the motor dont like 10/30!
thanks guys!

I had this neighbor years ago that worked nights. He was often leaving as I was getting home. He would start his Mercury Topaz and rev the piss out of it to "warm it up faster". It knocked like a stick in a 5 gallon bucket for the first 10 seconds each time. This went on for years. Some engines can take abuse better than others.

Piston slappage? Possibly too much clearance between piston skirt and cylinder wall only happens when cold due to piston shrinkage when cold. The hotter it gets the more it expands and then some of that clearance is gone. My two cents!!

now that i think back on this, the noise only came about after i switched from regular comp hyd, lifters over to pro magnum lifters....
theres only 15000 miles on the motor since it was rebuilt , so i doubt piston slap?