Piston Slap

[1998Dave]

Video of the knocking

So here I have a 7.4 vortec that I’ve noticed had this sound on cold starts. It’s got 163k on it and I’m the newest owner of her so I’m going through and getting all the kinks ironed out.

The knocking does seem to go away after a few minutes of running, it doesn’t get louder when you give it throttle (gets quieter if anything), and is mainly heard when your under the truck. I’ve never heard the infamous piston slap on an LS engine but I guess it’s common?

Anyways, if anyone has some insight or advice I’d greatly appreciate it as I’m all sorts of worried about hearing knocking engines!

 

[Groosalugg]

It's always a good idea to try running it with the belt off. Both see if the noise goes away and hear it better.

I personally couldn't hear anything in the video really with just speakers. Maybe different with headphones.

 

[1998Dave]

It's always a good idea to try running it with the belt off. Both see if the noise goes away and hear it better.

I personally couldn't hear anything in the video really with just speakers. Maybe different with headphones.

Appreciate you taking a listen, it is difficult to hear through a video but it definitely makes some noise in person. I’ve started it without the belt before to rule that out and it didn't seem to make a difference unfortunately.

 

[scott2093]

These are the most frustrating for me.... Sounds like the kind that gets all the possible answers...loose torque converter bolts...cracked flexplate....starter bendix ... etc... at least on my truck...

Like when I search for pain in my left leg.,.... I always take the least scary because it can inevitably be anything..

Have you tried some hose or a stethoscope to try and narrow it down?

 

[1998Dave]

I haven’t yet, I was planning on getting some soon to listen to try and track it down.

 

[ChrisRHC]

The 7.4 Vortec is not an LS engine, it is an old school big block engine.

I didn't notice anything out of the usual in your video. My 4.3 v6 has some piston slap when cold but goes away after 20-30 seconds and is 10x louder than your video.