4.3 Vortec top end knock - Blazer Forum - Chevy Blazer Forums

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4.3 Vortec top end knock

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Old 01-06-2019, 02:50 PM
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Default 4.3 Vortec top end knock

I have a 98 blazer that I just did a lower intake job on. After finally getting it to run, it has a top end knock. Not exactly a ping but fairly loud. It starts to go away around 3k rpm or very quite and on deceleration. I canít for the life of me find out whatís happening. Truck runs perfect. No miss and nothing leaking. All started after I did the lower intake gasket. Could it be a bad lifter or something stuck in the pushrod bore.
 
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Old 01-06-2019, 03:09 PM
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Does the sound eventually go away? Is it louder at certain times like when the engine is cold vs warm? How many miles on the motor? Those questions to me would determine if its a lifter problem or not.

If it comes and goes or lessens with the engine warm or cold, I would say probably a lifter. If so, drain a quart of oil out of the engine and add a quart of automatic transmission fluid to it and run the engine for 500 miles or so as it acts as a detergent to clean out any debris stuck inside the lifter.
 
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Old 01-06-2019, 05:54 PM
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Motor was rebuilt less than 20k ago. It does seems louder when it is cold and as i drive it more. About 15 minutes. It gets a little quieter but never fully away
 
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Old 01-07-2019, 07:57 PM
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Originally Posted by ForeverStomp View Post
Motor was rebuilt less than 20k ago. It does seems louder when it is cold and as i drive it more. About 15 minutes. It gets a little quieter but never fully away
Has the sound been there since the last 20k? Did it just recently start? What kind of oil are you using?
 
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Old 01-07-2019, 08:52 PM
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Just started after I replaced the lower intake manifold gasket. Ran beautifully beforehand. I was using 5w40 Castrol full synthetic as I always have since I built the motor.
 
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Old 01-08-2019, 10:54 AM
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Any update?

Have you found out which side the sound is coming from? Front or back? Top of engine or deeper in the engine? Put your hand on the valve covers as you rev the engine to see if theres any vibration or feeling of something unusual.

Is it a ticking or more of a knock?

From your posts, I would guess a lifter. Did you replace the lifters when the engine was rebuilt? Did you mess with any of the valve train when you had the valve covers off? Are you sure its an internal engine sound? Not trying to be a wise guy, just asking questions so you can do a process of elimination and pinpoint the general area of where the sound is coming from.
 
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Old 01-08-2019, 12:52 PM
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Driving it home last night and it kept bogging down and dying at stop lights. Sounds like itís more from the drivers side. Definitely top end. I rebuilt the motor because of rod knock and replaced everything on the motor except crank and cam. Decked heads and block. Bored it out just to be safe. The only thing I did when the valve covers were off was I checked to see if any rocker nuts came loose which they didnít but I feel as tho I may have snugged them up to much. But itís definitely internal. I appreciate everyoneís input. Just want my truck back on the road again. Thursday I plan on taking valve covers off and running the engine to see if I can see anything going on there.
 
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Old 01-08-2019, 01:23 PM
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Good luck to you.....Not sure why you needed a lower intake replacement if the engine is new 20,000 miles ago.

That abrupt stalling/stopping could be a big vacuum leak.
 
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Old 01-08-2019, 02:19 PM
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Yeah well I found it wasnít the lower intake gasket anyways. It was the top rad hose that would drip down the intake manifold. Stupid me. And I was thinking vacuum leak or something with a valve but idk. Iíll give an update Thursday as to what it was caused by
 
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Old 01-08-2019, 03:27 PM
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Updates are nice, hope its a simple fix for you.
 

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