AMC 258 CID (4.2 Litte) Engine Block Identification Numbers
AMC 258 CID (4.2 Liter)
Six-Cylinder: 258 CID (4.2 Liter) Engine Block Markings. Overhead valve gasoline engine. Cylinders are number 1 through 6 from front to rear (1 being the very front cylinder), in a firing order of 1-5-3-6-2-4. Crankshaft is on 7 main bearings and rotates in a clockwise direction, view from front of engine or vehicle. Camshaft is on 4 line bored bearings and is driven by the timing chain. Combustion is quench-type chamber (create turbulence and fast burning of air/fuel mixture for a good fuel economy).
Build Date Code
The engine Build Date Code is located on a machine surface on the right side of the cylinder block between the # 2 and # 3 cylinders. The numbers of the code identify the year, month and day that the engine was build.
Explanation Engine Build Date Code
Example: 3 10 C 11
1st Number Character is the build year: 3 = 1983, 4 = 1984
2nd and 3rd Number Characters is the build month: 01 = January, 12 = December
4th Letter Character code indicates the engine: C = 258 CID / 2v Carburetor / 9.2:1 Compression Ratio
5th and 6th Number Characters is the build day: 01, 02, 03 up to 31.
The example code 3 10 C 11 translate to: 258 CID (4.2 Liter) engine with 2V Carburetor and a 9.2:1 Compression Ratio, built on October 11, 1983.
Engines built for sale in Georgia and Tennessee have an additional, no repeating number, located on the right side of the engine below the build date code.
Example:
Kenosha-Build *E-1197277* or *W-1207177*
Oversize or Undersize Components Markings
Some engines where build with oversize or undersize components such as:
Oversize cylinder bores. Undersize crankshaft main bearing journals. Undersize connecting rod journals. Oversize camshaft bearing bores.
These engines are identified by a letter stamped on a boss between the ignition coil and the distributor. The letters are decoded as:
B = All cylinder bores: -0.010-inch (0.254mm) oversize
M = All crankshaft main bearing journals: -0.010-inch (0.254 mm) undersize
P = All connecting rod bearing journals: -0.010-inch (0.254 mm) undersize
C = All camshaft bearing bores: -0.010-inch (0.254 mm) oversize
Example:
Code letters PM mean that the crankshaft main bearing journals and connecting rod journals are 0.010-inch undersize.
