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Old 11-28-2012, 02:15 PM
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4.2L with loud tapping, what is this?

Sorry to hijack this thread but I am in desperate need of some help here. I have replaced rod bearings, oil pump, clutch, pilot bearing, fly wheel, cam, cam timing gear, crank timing gear, timing chain, lifters, rocker arms and exhaust manifold and I still have a loud chattering, does anyone have any idea what this might be?
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Old 11-28-2012, 02:51 PM   #2
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Is it tapping or pinging? Could be valve train, piston slap, or pinging from carbon build up. Did you have the head off? If so did you scrape all the built up carbon?

The 4.2 is noisy at best anyway, check your timing, EGR system, make sure it is getting vacuum. Mine in my '80 sounded like a Diesel due to wear, so naturally I ran 15W40 in it and it was great for another year until I hydro locked it, still managed to drive it home back firing and stalling the whole way, then I swapped in a AMC 360.

I'd say if your timing is good and EGR working properly, and you replaced all the valve train than its most likely piston slap, word is to put skirted pistons in to sort this issue.

Don't put that carbon removal crap in or it will clog your new pump.

If it were me I'd retire the old 4.2 and install a 350 SBC, you can find all the swap bits for cheap used, and the engines are a dime a dozen, and may net you better gas mileage.

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Old 11-28-2012, 03:21 PM
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It does sound like a diesel and when I had the head off it was fairly clean. Thanks for the help I'll check out the piston slap. Maybe it is just time for SBC.
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Old 11-28-2012, 07:51 PM   #4
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I tried all the old tricks on my 258, drained the oil and filled with ATF and ran it up to clean all the crap out. These old tricks work good but are just prolonging the death.
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Old 11-28-2012, 10:21 PM
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Hey thanks I appreciate all the help, hopefully I can get some more miles out of this old 258 before it dies completely but if it does die that will just give me a really good excuse to put the 350 SBC in it
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