Engine knock at start up (1 Viewer)

[Heffenoche]

I recently developed an engine knock at start up. It's not a a ticking or pinging noise, sounds more like if you took a rock and tapped it on another rock.

I would describe it as a moderate volume knock as it is apparrent with the hood up but cannot be heard from inside the truck. I've taken a stethiscope and is loudest when placed near the number 5 & 6 spark plug on the valve cover but can be heard from anywhere on the valve cover. It can bearly be heard when placed anywhere on the engine head.

Once warmed up the knocking is silent.

Would this be the valves being too tight and needing adjustment or something else?

 

[cruiserman]

Piston slap.

 

[Heffenoche]

Piston slap.

Which means...? I've heard of that but don't know what it is or how to fix. Can you give a little more explanation?

 

[cruiserman]

Here's a site on late model SBC & BBC piston slap problems. It's basically excessive clearance between the piston and the cylinder wall, which allows for a rocking motion of the piston in the cylinder. It's typically worse at cold startup and may go away as it warms up.

There are some threads in this forum on 80 piston slap.

 

[cheap 40]

Google search came up with this on top- http://www.pistonslap.com/
Apparently this is a common problem with GM engines.

 

[cheap 40]

Damn, beat me to it!!!!