AMC 6 identification

Need confirmation on engine identification. Stamped on pad is 704A11, on the block there are numbers 3218618. I read this as a 74 258 Sept block, am I correct.

7 is the year code, 04 is the month (4th month, April). Last two digits are day of month, and the letter is the engine size code.  Years code starts with 1 in 1959 and doesn't use a zero. It starts over in 1968 with 1 again. In 1980 AMC started using the last digit of the year, and started using a zero (1980 = 0). Repeats every 10 years -- Jeep used the code for the 4.0L through the end.

The engine size can be tricky. You need to know what size was made certain years as the letter code is reused as well. A could be a 199/1V or 258/1V. Since the 199 was made from 65-70, there is a slim chance you could have a 65 199 (7 is 1965 or 1974... or 1987). So you have to know something else about it -- like the casting number. I have 3218618 as a 70-72 casting number, shaft rocker head. The years aren't 100% accurate on most charts, not on mine since it's obviously a 74 block. I have another guide book where I've made corrections, but don't have it with me. Note: the 199 appeared in the 66 model year, but engines were coded for actual date of manufacture, and early 66 models will have 65 year built engines.

How can you be sure? Measure the stroke. You can come close by using a wire in a spark plug hole. Run a piston all the way down, mark the wire, then run the piston all the way up. 199 has a 3" stroke, 158 3.895". So if it's under 3.5" it's a 199, over a 258.

Of course if you know what the engine came out of helps. If a Jeep or 70s car you know it's a 258 (Jeep never got the 199).  If you don't know, check the stroke. 199 was only used in the 70 Gremlin and Hornet, other than that just Americans.


Edited by farna - Oct/16/2017 at 6:35am