How to tell if it is a 3.8 inline six or 4.2

[CoreyYoungCj577]

Ok so i havent really looked into this but i have a 77 CJ7 with a inline six and 3 speed tranny, but how do you tell if it is the 3.8L or AMC 258 i6 / 4.2l ?

 

[baker9713]

look at your engine build code found on the passenger side of the motor, stamped into a machined surface just below the head. The letter code in the middle tells what engine it is.
A- 199 1 bbl (70)
A- AMC 258 i6 / 4.2l 1 bbl (71-79)
B- AMC 258 i6 / 4.2l 1 bbl Low Compression (71-74, Jeep ONLY)
B- GM 151 2 bbl (80-83, GM 2.5L)
B- 126 Diesel (85-87, Renault 2.1L, Jeep XJ ONLY)
C- AMC 258 i6 / 4.2l 2 bbl (AMC 258 i6 / 4.2l , 76-89)
E- AMC 232 i6 1 bbl (70-79)
F- AMC 232 i6 1 bbl Low Compression (71-74, Jeep ONLY)
F- 145 Diesel (81-86, Jeep ONLY)
G- AMC 232 i6 2 bbl (70-74)
G- 121 2 bbl (77-79)
H- 290 2 bbl (68-69)
H- AMC 304 2 bbl (70-79)
J- 199 1 bbl (68-69)
L- AMC 232 i6 1 or 2 bbl (68-69)
M- AMC 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- AMC 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)