73-87chevytrucks.com
73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: Spool on July 09, 2019, 03:19:45 PM
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Hey Guys.
73' C20 Here.
I'm feeling a little foolish on this one...
I tapped out a snapped bolt (outer bolt for my starter) successfully, and installed the starter successfully, with great results.
No winding noise, no clanking, starts every time. Perfect.
However, I decided to rev my engine to the extreme a couple times to 'celebrate' afterwards and now I have this horrific 'woodpecker'
noise coming from my block. The noise happens more when I accelerate, less when in idle. I'm currently afraid to drive it out the driveway.
Any ideas as to what I broke?
Here is a video for the sound:
https://youtu.be/t4P_ipbTRdE
https://youtu.be/YpTGafvDuLs
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Remove the flexplate dust cover again. Slowly rotate the ring gear a few degrees at a time as you peer upward at the flexplate using a bright flashlight. Look for cracks and irregular rust tracks cutting across the face of the flexplate. Verify that the torque converter bolts are tight. Being mindful of spinning pulleys and belts, etc, use a three-foot-long 1" heater hose or similar rubber pipe as a listening tube and try to pinpoint the source of the noise.
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I'll have to familiarize myself with all of this in a day or two when I'm under the truck.
But may I ask, why do you think the noise would be coming from the transmission?
When I was on the front side of the engine, and gave it fuel from the carb, the noise was so loud that it sounded as if it was coming from cylinder 1,
which what led me to believe it was inside the block.
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I didn't suggest the noise is emanating from the transmission. But it could be coming from a popping flexplate or loose converter bolts.
The sound clips you posted seem too high pitched and shallow (almost tinny) for the mass of the rotating assembly (rods/crank), which create a much deeper and more pronounced metallic thud like the impact of a very large hammer. Did you notice any change in the engine oil pressure since the noise began?
I've encountered broken crankshafts that make a similar noise. Try prying the balancer fore and aft. Then repeat the process at the flexplate end of the crankshaft. How much axial (end-to-end) movement is there? Is there more movement at one end than the other?
If the rattle was emanating from under the valve cover (tossed rocker arm, broken spring or collapsed lifter), it would likely be associated with an engine misfire. The metallic rattle sounds more like a broken bracket or possibly loose or broken pulley. Inspect the harmonic balancer and the crank pulley for looseness/cracks. Make sure the outer ring of the balancer isn't drifting forward or aft, exposing the elastomer band between it and the hub. Another possibility is some debris on top of a piston in one of the cylinders. Try removing the spark plugs and inspecting the electrodes for evidence of impact or detonation damage.
Of course, you have the advantage of being there to hear the noise first hand. The sound clip might be deceiving and covering a deeper, more troubling sound.
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I should add, the troubling aspect of your description is that the sound began abruptly, coincident with revving the engine. The initial checks that I recommended don't require you to start and run the engine. If a rod has indeed failed, you don't want it to separate from the crank pin and window the block. So, avoid running the engine as much as possible until you have better identified the source of the noise or at least narrowed it down through elimination. If you discover nothing peripheral to the motor causing the noise you may wind up removing the oil pan for internal evaluation.
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Yeah, too light to be metal.
I bet you have old fan belts and in your jubilation of revving, you threw a chunk of V section out and its flopping...
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Just going back through old threads here.
To bring this thread to a conclusion-
The noise heard was actually a snapped rocker arm.
It has since been replaced and all is good.
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Just going back through old threads here.
To bring this thread to a conclusion-
The noise heard was actually a snapped rocker arm.
It has since been replaced and all is good.
My favorite type of post! thank you for bringing us to a finally my friend. The most annoying thing i find is searching through a whole thread hoping for some light on a subject and never having a conclusion. Once again I thank you!