1997 5.7 Vortec Engine Knock/Tap

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97Suburban

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Hello,
I have 1997 Suburban K2500 with the 5.7 Vortec Engine and it has a knocking/tapping noise. The noise goes away but it comes back as well. I took some videos of the noise to make it easier to describe. I wanted to know what would be the best course of action to try and fix this. There are no codes on the dash.
Video
Thank You.
 

JOHNGAAA1

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Sounds like a fan noise, fan clutch, shroud, water pump wobbling, etc. When you rev it the fan clutch engages and the noise stops. Start there.
 

Vanishing Point

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May I suggest a mechanic hearing stethoscope (obtained from your local parts store for purchase or rent?) to telegraph your vehicle's engine sounds? Do not put it directly on moving spinning parts? Once you get underneath your Truck, ascertain if the noise is more audible coming from the top of your engine's left or right side front or rear instead of the noise emanating from underneath the bottom left/right front or backside of your engine? Put one end on your ears, the other steel pointed end on the flywheel cover, and anywhere else on top of your engine (valve covers) to listen for loose tappets or rocker arms.
If you feel you hear tapping clicking noises and it gets louder as you move the pointed end around, you may have zeroed in on the problem area where something may be loose, like a (flywheel bolt) especially if the noise is more audible coming from underneath towards the back of your engine.
Also, check for any new fluid leaks such as (windshield washer, antifreeze coolant, motor oil, power steering, and automatic transmission ) that may have fallen on worn surfaces and any other rubbing shiny metallic surfaces. Good luck, and lets us know how it turns out.
 

97Suburban

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Sounds like a fan noise, fan clutch, shroud, water pump wobbling, etc. When you rev it the fan clutch engages and the noise stops. Start there.
I'll check the fan clutch. Thanks.

May I suggest a mechanic hearing stethoscope (obtained from your local parts store for purchase or rent?) to telegraph your vehicle's engine sounds? Do not put it directly on moving spinning parts? Once you get underneath your Truck, ascertain if the noise is more audible coming from the top of your engine's left or right side front or rear instead of the noise emanating from underneath the bottom left/right front or backside of your engine? Put one end on your ears, the other steel pointed end on the flywheel cover, and anywhere else on top of your engine (valve covers) to listen for loose tappets or rocker arms.
If you feel you hear tapping clicking noises and it gets louder as you move the pointed end around, you may have zeroed in on the problem area where something may be loose, like a (flywheel bolt) especially if the noise is more audible coming from underneath towards the back of your engine.
Also, check for any new fluid leaks such as (windshield washer, antifreeze coolant, motor oil, power steering, and automatic transmission ) that may have fallen on worn surfaces and any other rubbing shiny metallic surfaces. Good luck, and lets us know how it turns out.
Good idea. I'll get one and start checking.
Weird that it's so erratic.

I would not want to rent anything that's been in someone else's ears :eek:

Mine is from Harbor Freight, and I don't think cost much.
It's $5 at Harbor Freight so I'll pick one up from there.
 

97Suburban

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I did a compression test, I got ~150 psi on all cylinders. I took the valve covers off and all the rockers were moving. I tried lowering the spark plug gap as well. I took the belt off and ran the engine and the noise was still present. One weird thing was when I was changing gears (P->N->R) the noise stopped for a second and picked back up. I tried changing gears the same way a 2nd time but the noise stayed constant. Revving the engine slightly increases the noise as well. What's weird is that sometimes for a moment the noise goes away so its not 100% permanent.
 

Pinger

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Is it a trick of the light or are there 'bits' flying from behind the radiator when it's revved?
 

wirlybird

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One thing that is possible is that it is piston slap. My 97 Tahoe with a 5.7 Vortec started getting a light knocking sound when cold that would go away after a bit.
Researching I found that this could be due to short skirts on the pistons that let them rattle a bit when cold.
Mine has now done this for 230,000 miles, truck has 330,000 on it now. I also read many stories of other with the same issue and have put on a lot of miles with no ill effect.
Mine uses no oil and the oil is nice and clean at changes so no indications of bearing or other issues so far.

Google Vortec piston slap or Vortec knock and see what you find.
It MIGHT be what you are experiencing.
 
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