350 engine knock

I have a 97 z71, when I start the engine (cold) it has a deep knock, almost like a deisel, after 30 sec. it quits and sounds fine, while haveing the tranny rebuilt I put in new main and rod bearings, the clearances checked
fine, but this didn't fix the problem, any Ideas? Thanks, John
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I use to have a Buick which has done the same thing. My mechanic told me that it was the oil, which was circulating into the system. After about 5 minutes, it has quiet more down until you could not hear anything. It has just done it when the engine was cold, the first thing in the morning. But your problem could be different than it was mine.
John M Nofziger wrote:

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"Gunes" wrote

Your mechanic is feeding you a line of bullshit. If it took 5 minutes to develop enough oil pressure to deal with a "knock", your engine would be toast on the first startup. Full oil pressure is achieved allmost instantaneously...other wise your motor will be destroyed very quickly. 4-5 seconds is the max amount of time before a normal engine develops full oil pressure at the guage, and that is after an oil change, without the filter being filled.
Ian
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"John M Nofziger" wrote

You probably have a bit of the "infamous" piston slap. This affects even the older style "Vortec" engines, tho it doesn't get a lot of press. I often hear this noise on the old style small block chevy, but it's not nearly as common on these engines as on the new style chev small block. If the noise disappears within 30 seconds, I wouldn't worry too much about it. I can't remember ever replacing pistons or doing anything to try to rectify this type of noise in that year of truck.
Ian
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Is it a knock like a rockerarm assembly?(head tapits). Maybe you could experiment with a different type of lube. Now that the engine is older it could respond in a strange way. How cold is cold? I've heard of that happening in quite cold conditions. I hope that helps.
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I have a similar problem on my 1997 tahoe and have been told that it is caused by wristpin knock. I'm not sure if this is the case or not since at 120,000 I'm not to apt to go and rebuild or replace the motor. Let me know what you find out.
Mike
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I had the same problem with a engine I bought from a wrecking yard. The new oil filter (cheap one) was defective. I changed to a quality NAPA filter for the fix. Good luck, DC
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I have the same truck as you do.Mine does that to when it`s cold.I haven`t found a solution for the problem except for pulling the motor out.It`s VERY common and not hurting anything. Just wait till the noise stops before you drive and all will be fine. How many miles do you have? Mine has 75,000
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Thanks for the info everybody, the truck does have 125,000 miles on it, I live in Ohio so at 0 degs. it is bad but as the weather warms it gets better, I have tried different grades of oil and oil filters to no avail. so I guess I'll just live with it. John

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it could be a carbon knock i had a 97 s10 blazer 4.3 vortech with 60 000 miles that did the same thing pulled the heads and carbon was real thick once i cleaned the pistons and put the motor back together no more noise the 4.3 v sucks is just a 350 with 2 less pistons bell housings are the same
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Re: 350 engine knock Group: alt.autos.4x4.chevy-trucks Date: Sat, Feb 28, 2004, 11:08pm (PST+3) From: snipped-for-privacy@webtv.net (JasonTaylor) it could be a carbon knock i had a 97 s10 blazer 4.3 vortech with 60 000 miles that did the same thing pulled the heads and carbon was real thick once i cleaned the pistons and put the motor back together no more noise the 4.3 v sucks is just a 350 with 2 less pistons bell housings are the same _____________________________________ Jason,just out f curiosity did you find the cause of all that carbon in your 4.3 ?What was the cure and how long did the job take?
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happening to my 97 Z71 with a 305.120,000 miles .The knocking started two days ago in the morning but today it's fine. Going to give her some synthetic blood and new filter and see how that goes. Rob. love this site!
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Rob, let me know if the synthetic helps, I was wondering about slick 50 or something similar. Thanks, John

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350 engine knock Group: alt.autos.4x4.chevy-trucks Date: Tue, Feb 24, 2004, 7:45pm From: snipped-for-privacy@fulton-net.com (JohnMNofziger) I have a 97 z71, when I start the engine (cold) it has a deep knock, almost like a deisel, after 30 sec. it quits and sounds fine, while haveing the tranny rebuilt I put in new main and rod bearings, the clearances checked fine, but this didn't fix the problem, any Ideas? Thanks, John two words: piston slap! not much to do except new pistons, which woud be a waste. best of luck -pete
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