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What would a wrist pin sound like?

 
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Old 10-21-2010, 11:39 PM
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What would a wrist pin sound like?

still trying to figure out the noise in my 390. its certainly NOT exhaust, I've followed that road to its end with new header flanges welded on and welding up the ENTIRE exhaust, yes its gonna be a PITA to get back off, but I'm sick of this noise. Its a higher pitched tap or click that shows up at 1500 rpm, mostly under NO load, by 1600 rpm its gone, then kinda fades back in and i can hear it at a 2k cruise, i dont hear it under acceleration. what type of sound would a wrist pin make? i've checked the valvetrain 100 times with covers off and motor running and could not pinpoint the sound. i hear it very clearly from under the truck as well. should i pull the pan this weekend?
 
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Old 10-22-2010, 07:14 AM
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I think I am correct in saying a wrist pin bushing will tick, tick, tick, constantly. The one in a 390 that I had was heard from idle to hi-way speeds never stopped.







John
 
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Old 10-22-2010, 01:21 PM
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pulled the pan and the bottom end is as tight as prom night, nothing wiggles or budges on the top or bottom end of the rods. the only thing that seems loose is the comp timing chain i put on around 5k ago, its easily got 1/2" of deflection on the left side (looking at the motor, 1-4 side), seems out of spec to me but my manual doesnt list a spec for timing chain deflection, any ideas?
 
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Old 10-23-2010, 01:22 PM
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Originally Posted by mabigredtruck View Post
still trying to figure out the noise in my 390. its certainly NOT exhaust, I've followed that road to its end with new header flanges welded on and welding up the ENTIRE exhaust, yes its gonna be a PITA to get back off, but I'm sick of this noise. Its a higher pitched tap or click that shows up at 1500 rpm, mostly under NO load, by 1600 rpm its gone, then kinda fades back in and i can hear it at a 2k cruise, i dont hear it under acceleration. what type of sound would a wrist pin make? i've checked the valvetrain 100 times with covers off and motor running and could not pinpoint the sound. i hear it very clearly from under the truck as well. should i pull the pan this weekend?
Had the exact same issue some 10 years ago with a 390
the fuel pump spring was loose causing the noise...drove me crazy tore the engine apart and never found a thing wrong...was the fuel pump lever spring..just a thought
 
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Old 10-24-2010, 09:36 PM
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with it running, at the rpm range where the sound is loudest, pull the plug wires, one at a time, see if the sound is cylinder specific, good indication if it is a wrist-pin
sound will stop if it is a wrist-pin,
when you had the pan off, did you unbolt the rods to check for wear and allow you to physically wiggle the rod to check that the wrist-pins are tight?

if there is no change in the sound, my guess is that it is accessory related, fuel pump, water pump bearings, etc.
 
 
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