Y87bird00

iTrader: (6)

Hey guys, I am trying to find out what is causing this embarrassing knocking when I cold start my motor. It is a 5.3 with ls6 cam and intake, milled heads, and longtubes. It doesn't always happen, sometimes it'll knock once or twice, other times it knocks like in the video. Any ideas on what it could be? It goes away when it revs, and gets hot. It doesn't do it on a hot start.

goldta78

It's hard to hear over your exhaust, but the 5.3 in my silverado used to have really bad lifter chatter when it was started cold. Changed my oil never had the problem since... It was really loud.

Y87bird00

iTrader: (6)

It sounds like a very solid knock, not like I imagine from a lifter. It has brand new ls7 lifters. I'm thinking it might be the long tubes rattling against something in the bay when the motor rocks real bad. It's got stock rubber mounts. Sometimes the idle drops and bounces near 300rpm and back to 500 and the motor with rock and knock. Only on cold start up

ls1 1990 VN

Almost sounds like a loose baffle in a muffler

Y87bird00

iTrader: (6)

It reminds me of the sound it made a while ago when the torque converter bolts backed out. But those got faster when revved and never went away. I've already checked them. It's coming from the back of the motor ish.

Y87bird00

iTrader: (6)

Here is a knew cold start video, no knock

flattusmaximus78

iTrader: (1)

Whats your exhaust set up?

I run longtubes, 3.5" y and 4" to a single muflex dumped. Use to not make any noise. No with the cam the exhaust rocks so much on cold starts, It sounds like my muffler smacks the floor board, but it's tight as can be. Def my exhaust though, just a thought. That doesn't sound engine related though.

Y87bird00

iTrader: (6)

It's pacesetter longtubes, tsp ory, and 3" to the muffler. I know the pipe hits over the axle when driving but not idling. I think it might be hitting the steering shaft on the drivers side

Old Geezer

iTrader: (3)

My 08 Silvi w/ the 5.3 does that sometimes, on cold start, when the oil needs changed. I use the factory dash warning at 7500 mi. Change it..no more noise.

sic7camaro

iTrader: (21)

My moms suburban does it on cold start.it use to.sounds like a spun rod bearing. Rod knock.

chrisfrost

iTrader: (8)

It's piston slap,,,,,,,,,,,all the LS based gen3/4 engines are prone to this . Search piston slap and You'll see a Bunch of threads.

Y87bird00

iTrader: (6)

It sure doesnt sound like the examples of piston slap I've heard

Y87bird00

iTrader: (6)

To come back and answer this, it was loose torque converter bolts. I have no idea why it was only on start up, but that's what it was.

Bama99z

iTrader: (7)

Congrats on it just being loose convertor bolts. My luck it would of brrn something internally.

Burken01

iTrader: (88)

What were they initially torqued to?

Y87bird00

iTrader: (6)

'Tight' I couldn't get a torque wrench in there. But I used red locktite and arp bolts this time

Burken01

iTrader: (88)

As long as the bolts don't bottom out into the converter pads then you should be fine..

I didn't use loctite, but I torqued them to 55lbs (arp) bulk bolts

Hope it holds up,

Y87bird00

iTrader: (6)

Thanks. I had the bottoming out problem last time with dealer bolts, and 20mm long bolts. That's why I went arp. It held up good so far