Source page for this data: amcrc.com
UP TO MID 1967:
Some engines will have a second three letter code under or beside the serial number or Day Build Code. This code is used to indicate under and/or over size parts. All three letters will be present if any part was factory altered from original specifications. If .010 inch over or under would not correct the fit of the part(s), they were replaced. No engine was fitted from the factory with parts that were over .010 inch above or below standard.
The code represented the bore (1st letter), main bearings (2nd letter), and rod bearings (3rd letter). In any position, an "A" indicates standard size, "B" .010 inch undersize, and "C" .010 inch oversize.
The code is located directly below the serial number or Engine Day Build Code on 172-195.6 six cylinder engines, on the boss directly above the oil filter on 199-258 six cylinder and AMC built four cylinder engines, and on the valve cover tag on V8 engines.
MID 1967 AND LATER:
A different letter represents each part and the modification. The letter is located on the boss directly above the oil filter on six cylinder engines, on the valve cover tag on V8 engines. One or more letters may be present:
B- 0.010" oversize cylinder bore
C- 0.010" oversize camshaft bearing bore
M- 0.010" undersize connecting main bearings
P- 0.010" undersize connecting connecting rod bearings
AMC used a the "Engine Day Build Code" as a serial number for all engines starting in 1960. This code gives the date the engine left the assembly plant fully running and has a code for the engine size/type.
NOTE: This code is NOT necessarily the same as found on the VIN. In some cases it is, but often the VIN code changed whereas the build code remained for any size engine.
An important thing to remember about AMC engines is that changes were made on a calendar year basis, not model year. The engine plant ran on its own schedule! This is why some 1980 model vehicles have the "heavy" 258 and others the "light" 258 -- changes were made early in calendar year 1980.
The Engine Day Build Code consists of six characters:
1. Year built code 2 & 3. Number of the month 4. Engine size/type code 5 & 6. Day built
Thus, "409C21" indicates 1962, September, 195.6 OHV (cast iron), 21st day. The only way to determine the year is 1962 instead of 1971, 1984, or 1992 is to know that the 195.6 OHV engine was discontinued after 1965, and what a 195.6 looks like (very different than the 199/232/258). Most codes do not overlap very much. For those that do (such as 3 -- 1961, 1970, 1979, 1983, 1993) casting numbers may have to be consulted if the engine date is important, such as for a restoration.
| 1=1959 2-1960 3=1961 4=1962 5=1963 |
| 6=1964 7=1965 8=1966 9=1967 1=1968 |
| 2=1969 3=1970 4=1971 5=1972 6=1973 |
| 7=1974 8=1975 9=1976 1=1977 2=1978 |
| 3=1979 |
| Beginning in 1980 the last digit of the year is used (1980=0, 1981= 1, etc.) |
Engine Size/Type Codes
1960-1967: AMC complicated things these years by using a different code in the VIN of each model for the same engine in at least 66 and 67. This confuses many sources! The codes below are used in the Engine Day Build Code, which is the same for all models. Serial number codes will be found with serial number decoding information. Years following code is the years the engines were available.
A- 195.6 1 bbl (60-65, L-head)
A- 199 1 bbl (66-67)
B- 195.6 (61-64, OHV aluminum, 1 or 2 bbl)
C- 195.6 OHV (61-65, OHV iron, 1 or 2 bbl)
D- 250 (60-61, 2 or 4 bbl)
E- 327 2 bbl (60-66)
F- 327 4 bbl (60-66)
G- 287 2 bbl (63-66)
H- 290 2 bbl (66-67)
J- 199 1 bbl (66-67)
L- 232 (64-67, 1 or 2 bbl)
N- 290 4 bbl (66-67)
Z- 343 4 bbl (67)
1968-2001: Someone at AMC decided to simplify things, or maybe the U.S. Government decided for them since engines now had to be qualified for emissions by type and size? In any case, all models used the same codes for the same engines.
Some codes were used for more than one engine. Year ranges are given for code use.
VIN and engine code numbers are different! This can be confusing. The 4.0 has an engine code of MX, but there are three different VIN codes (M, L, S). The earliest VIN code usually matches the engine code, later versions of the same engine may have different VIN codes but engine code usually remains the same.
A- 199 1 bbl (70)
A- 258 1 bbl (71-79)
B- 258 1 bbl Low Compression (71-74, Jeep ONLY)
B- 151 2 bbl (80-83, GM 2.5L)
B- 126 Diesel (85-87, Renault 2.1L, Jeep XJ ONLY)
C- 258 2 bbl (4.2L, 76-89)
E- 232 1 bbl (70-79)
F- 232 1 bbl Low Compression (71-74, Jeep ONLY)
F- 145 Diesel (81-86, Jeep ONLY)
G- 232 2 bbl (70-74)
G- 121 2 bbl (77-79)
H- 290 2 bbl (68-69)
H- 304 2 bbl (70-79)
J- 199 1 bbl (68-69)
L- 232 1 or 2 bbl (68-69)
M- 304 2 bbl Low Compression (71-74, Jeep ONLY)
MX- 242 MPI (4.0L MPFI, 86-01, Jeep ONLY)
N- 290 4 bbl (68-69)
N- 360 2 bbl (5.9L, 70-91)
P- 360 4 bbl (70-77)
R- 134 1 bbl (70, F-head, Jeep ONLY)
S- 343 2 bbl (68-69)
T- 134 1 bbl Low Compression (70, F-head, Jeep ONLY)
U- 150 (84-01, AMC 2.5L, Jeep & Eagle ONLY)
W- 390 4 bbl (68-69)
W- 173 2 bbl (84-86, GM 2.8L V6, Jeep XJ ONLY)
X- 390 (70)
Y- 390 (70 Machine)
Y- 318 MPI (93-96, Chrysler 5.2L, Jeep Grand Cherokee ONLY)
Z- 343 4 bbl (68-69)
Z- 401 (71-77)
For more information on AMC cars check the "American Independent Magazine" website: http://home.att.net/~farna . An "AMC Annual" is published yearly listing all known AMC and related makes clubs. There may be one in your area! The AMC Annual may be purchased without subscribing.
The very best thing you can do for your AMC is join a local club. If there are no local clubs, you should still consider joining one of the national clubs. AIM offers information and some support for ALL AMC vehicles, the clubs tend to gravitate toward specific interests and offer some support, such as holding meets at many locations across the country, that AIM can't. Even if you do join a local club, you may be interested in services from one or more of the national clubs as well. But if you are a genuine "AMC nut", subscribe to AIM to get a REAL fix!
Frank Swygert -- Gulfport, MS
Publisher, "American Independent Magazine" (AIM)
Supporting all AMC related vehicles, 1902-1987
Website: http://home.att.net/~farna