So it only lasts for the first 5 seconds when you crank it??

 

i'm not sure what kind of tappets (lifters) are in these engines but if it happens early upon start up and goes away, could it be a lifter sticking untill it gets oil? after listening to the video, it kinda sounds like thats what it could be. if it was a gasser i would put a dollar on it. thats the same sound a lifter makes sometimes.

 

happens after you start it cold. lasts for 10 seconds. then goes away .ill use my stethescope

 

on sunday ill pull the serpentine belt and start it cold...

 

Yep that what i was thinking, you would be surprised how long it takes for oil to circulate throught the engine...

 

i put stethiscope on valve cover and sounds normal.

 

No hydraulic lifters in these engines which are what can stick before getting pumped up.

They are mechanical flat tappets which, unlike hydraulic, require a lash adjustment.

The lash gap is largest when the valves are cold. The gap will shrink when they get hot. If there is too much lash, it could be possible that they could be slightly noisy when cold and slowly quiet down when the warm up. Though, I have never come across a CTD that was noisy because of too much lash but it might be possible.

I think .010 on the intake and .020 on the exhaust is probably plenty. You could even tighten that up a few thou on each. Either way, it is worth checking.

 

sounds like piston slap on gm engines.

 

Can you here it better from the front or the side? If better from the front ,then remove the belt.

 

only from the front. sunday morning ill try this. im going to remove the serpentine belt, then remove the ECM fuse so the truck wont fire up, then turn starter over for 10-15 seconds.(to allow oil coolers to shoot oil up under piston). Then ill put ecm fuse back in and try and start it. if its quiet then its wrist pin clearance and the oil is what is making it quieter and smaller tolerance.ill try serpentine belt thing first.

 

Had one come in the shop last week with the same noise.
It was the top bolt on the altenator worn half way through from being left loose at some point in time.
Replaced the bolt, tightened all the others, and the noise was gone.

 

WAS IT ONLY AT STARTUP? or all the time? this goes away sometimes after 3 seconds. sometimes after 15...

 

Yes, only at srart up and then it would go away.

 

removed serpentine belt and truck sounds like a cadillac. no knock?

 

spun alt,water pump,ps pump,pulleys etc.. all were good. noticed fan slightly hitting bracket that feeds wires to thermatic fan. bent it back. fan doesnt rub now. put belt back on. started it and no noise.???????ill try again tommorrow morning with belt on and cold start.