Vortec knocks when cold

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97__Z71

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Every time I start my truck in the morning it sounds like it knocks, but then it goes away after a couple of minutes. Oil pressure is 60-80 cold idle 30-40 hot idle. From what I've herd this is a common issue with these trucks and that people call it a "Piston Slap" and that it isn't bad. I'm just curious to know what exactly is going on.
 

Tempted

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Not just Vortec, pretty much all 88+ small blocks. I've been lucky, my 94 doesn't suffer from it. All my other 88+ trucks did. Even my 99 5.3 does. Just a thud thud thud, then its fine. Mine have only done it for a few seconds, though, not minutes. I'd be a little more concerned if it lasted a while.
 

97__Z71

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I had a 93 that had a 350tbi I never heard a sound when it started cold. I know a few people that have 5.3's and its a lot worse than mine. From what I understand its a bigger problem in the GMT800's.
 

DRAGGIN95

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I had a cold knock on our 99 burb with vortec 350, it did that for it's last 6 month's of life, then it died. I have never experienced it with any other gen 1 smallblock though!
 

TruckinAin4Sissies

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O yeah, sounds like a 12v-Cummins huh? Yep, mine does that for ~3 minutes when cold.

Carbon builds up on the piston rings and creates a (minute) gap in the cylinder walls. After the oil circulates enough/warms up slightly then they free up (expand) and no more knock.
 

redneck98

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O yeah, sounds like a 12v-Cummins huh? Yep, mine does that for ~3 minutes when cold.

Carbon builds up on the piston rings and creates a (minute) gap in the cylinder walls. After the oil circulates enough/warms up slightly then they free up (expand) and no more knock.

mine does the exact same thing
 

Tempted

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That is a long time to have a knock, 3 minutes. I'd be rebuilding/replacing it.
 

97__Z71

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Well I guess I'm just gonna have to wait it out and see what happens. I've had this truck for three years and it has 190k miles on it. Its knocked when its cold outside for as long as I've owned it.
 

Tempted

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It would be a perfect time to start putting together then gen 1 of your dreams. A good old 4 bolt block to start, add the goodies as you go. That is how I used to do it, after a few times you'll end up with an extra engine or two laying around at the shop.
 

PlastiKTuneR

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My 98 Suburban knocks when cold as well. Not for long, but it always has, I've owned it 2 years, it also has a rebuilt engine. 340,000 on the clock.
 
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