how to tell the year of 4.2 -
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post #1 of 3 Old 05-02-2010, 07:59 PM Thread Starter
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how to tell the year of 4.2

recently bought a 4.2 for second jeep that i rebuilding how ever dont know if it is a earlier 70's motor or if it is a 80's motor/ because the size of main and rod bearings changes any input would greatly help... thanks you all...

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post #2 of 3 Old 05-02-2010, 08:47 PM
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1980 CJ7 
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post a pic, that will help for starters, and look for casting numbers.
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post #3 of 3 Old 05-02-2010, 10:20 PM
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1991 YJ Wrangler 
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Look for the numbers stamped on the pad between #2 and #3 sparkplug

then refer to this page to decode

91 YJ Sahara, 4.0L, AX-15/NP231, D30/D35@3.07
12 Cherokee 4x4,3.7L,42RLE/MP1522, D30M/8.25@3.73
Emission test=YES
"Non Vi Sed, Arte"
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