Editing AMC straight-6 engine (section)

===Connecting rod lengths===
'''1964–1970:'''
*{{cvt|199|CID|L|1}} — {{cvt|6.125|in|mm}}
*{{cvt|232|CID|L|1}} — {{cvt|5.875|in|mm}}
*{{cvt|252|CID|L|1}} — {{cvt|5.875|in|mm}}

'''1971–2006:'''
*{{cvt|232|CID|L|1}} — {{cvt|6.125|in|mm}}
*{{cvt|242|CID|L|1}} — {{cvt|6.125|in|mm}}
*{{cvt|258|CID|L|1}} — {{cvt|5.875|in|mm}}
*{{cvt|282|CID|L|1}} — {{cvt|5.875|in|mm}}
*The [[Engine displacement|displacement]] differs between 1990–1995 and 1996–2006 versions of the 4.0&nbsp;L engines by around {{cvt|1.7|CID|L|2}}. Both had a bore of {{cvt|3.875|in|mm}}, but the stroke decreased slightly from {{cvt|3.4375|in|mm}} on the earlier engine to {{cvt|3.414|in|mm}} on 1996 and later engines. The small stroke change of {{cvt|0.03|in|mm}} was accomplished by moving the piston pin and changing the crankshaft stroke; the rod length did not change.

The deck height of the AMC six-cylinder block was increased by {{cvt|1/8|in|mm}} (half the rod length difference) in 1971 to allow for the longer stroke required for the 258. There are only two deck heights. Tall deck is {{cvt|9.528–9.534|in|mm}}. Short should be {{cvt|9.278–9.284|in|mm}}. Tall is from 1974 through 1976 AMC factory service manuals; before 1974, deck height was not printed. Deck height changed slightly over the years 1977–1982 service manuals state {{cvt|9.487–9.493|in|mm}}, the 1993 Jeep factory manual states {{cvt|9.429–9.435|in|mm}}. Deck heights may have changed to accommodate slightly different compression ratios over the years.<ref name="74 AMC Technical Service Manual">{{cite book |title=1974 ANC Technical Service Manual |year=1974 |publisher=American Motors Corporation |section=Group 1A, Six-Cylinder Engines |page=1A-31}}</ref>

The 1971 and older blocks use a "small" bell housing bolt pattern exclusive to AMC and small Nash sixes. In 1972, the bell housing bolt pattern was changed to match the AMC V8s. Its final use was in 2006 when the 4.0&nbsp;L was phased out. Four bolts on the cylinder block are matched to the transmission bell housing where an adapter plate serves as a dust cover — two additional bolt holes on the transmission bellhousing used on the AMC V8 are used to secure the dust cover. The 1971 model year 258 uses the "small" pattern, the only version of the 258 to do so.