Can someone explain to me the differences in the subject engines as well as years of manufacture.
Basically completely different engines right down to the crank and block. The only similarity they really have is that both have 6 cylinders. If you give a little more information about why you are asking someone may be able to help further.
One of the things with these two engines that confuses me is how Cat, at least in SIS, can seem to lump them together. Even to the point of using the same S/N prefix. One example is the 66D series. From 66D00001-08890 it is a D333C engine and starting at 66D08891 it is shown as a 3306. And the fact that some parts like rocker arms and lifters are the same between the two engines. I know on this forum more than once it took some work to determine which engine was actually the one used in a particular machine to the point that it seems Cat phased out the D333 in the middle of a production run of one serial number prefix of say a track type tractor or track loader, that being in at least one case a D330/3304 four cylinder version of the engine.
I have 2 gen sets, one is a MEP007A w/ a 333C and the other is a MEP007B w/ a 3306. The engines look very similar and have the same bore and stroke. Years ago I had a 977K 11k series which had the 333C ( earlier 977H and K models had the smaller bore / stroke 333 ) and then later I owned a 977L 11k series model introduced in 1972 w/ the 3306, ROPS, inside mounted carrier rollers, and other minor changes. I can't remember if it was a spacer plate engine. The 3306 engine I installed in my 130G 9Y6 / 140G conversion came from a salvage 1984 MEP007B and is a PC version, seems military hangs onto older configurations. It would seem that DI would be better, but the military has their reasons. I appreciate the input being provided.
I did not research real deep but did seem to get the impression that the D333C was somewhat of a middle step between the D333 and the 3306. I was thinking the D333 was a slightly smaller bore than the 3306.
One of the two has a keyed injection pump shaft and the other does not as well. I agree with kshansen that it was a mid step. I think it is closer to the 3306 than the D333 it replaced.
The man that overhauled my trans and torque has converted a few 333c to a 3306 so they would bolt up to the 3306 configuration. The only one that wont work is the 333 with the smaller bore. The blocks look different from the outside small bore to big bore.
I want to say the d333 was 4.5" bore and the d333c/3306 was 4.75.
you are correct 333 small bore 333c/3306 big bore