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Depending upon the year and engine source, 4.2L AMC/Jeep®/I-H version timing covers can be different than a 4.0L cover. The TDC mark may be many degrees away from the 4.0L damper mark, which is typically the damper used in a Mopar EFI conversion. Determine the true TDC for #1 piston when referencing TDC; this is determined by measuring the piston's position in #1 cylinder with the spark plug removed. The piston must stand at its peak when determining TDC. Note: Inexpensive TDC tools are available at Summit, Amazon and elsewhere: https://www.summitracing.com/parts/sum-900189 or TDC
The timing cover on a 4.2L is different than the 4.0L. TDC mark is many degrees away from the 4.0L damper mark, which is typically the damper used in a Mopar EFI conversion. Use true TDC for #1 piston when referencing TDC. If your damper mark does not match up with #1 piston TDC, place the #1 piston at true TDC and scribe a timing mark on the damper to match the timing cover TDC. This is one builder’s 4.0L/4.6L experience. He has a 4.0L in a ’98 TJ Wrangler and installed an OE 4.2L/258 crankshaft. The 4.2L crankshaft keyway did not match his OE 4.0L crankshaft keyway position: