GMC 256 Engine Questions

[Hardbird]

Hello All,

The engine (256 CID) that I have questions about was used in GMC produced AFWX and ACKWX trucks (thanks for this information, and more, goes out to Mr. Joel Gopan)

Which oil pan would the 1940 through 1941 GMC 256 engine use? From what I have been able to find out, I am guessing that it would be the "shallow" pan.

Also: are the crankshafts, camshafts, timimg gears, and connecting rods the same between the 256 and the 270? Or are they different? If so, what are the differences and what casting numbers should one look for?

And how about the push rods (my guess is that they are shorter due to the difference in block height)?

There is very little information available about these early trucks and their engines, and I am just wanting to verify things.

I think that these are one of the most overlooked vintage GMC trucks out there.

Regards,
Ron Leatherman

Here are links to what these trucks look like if you are curious:

1940 AFWX 354 3-Ton 6X4 truck:

http://www.o5m6.de/gmc_afwx354.html


1940 ACKWX 353 3-Ton 6X6 truck:

http://www.o5m6.de/gmc_ackwx353.html

[dr deuce]

The 256 has a different block. Shorter as I recall. The crank and conn rods are different too (from memory). Mixing some of these parts is disastrous!

[Hardbird]

The 256 has a different block. Shorter as I recall. The crank and conn rods are different too (from memory). Mixing some of these parts is disastrous!

Dr. D,

With the 256 being produced for less that a year, it is the "forgotten" GMC engine. It is rarely, if ever, mentioned. With this being the case, there is very little publicly written information about these engines available.

Those who have this informtion have it in either their minds or in their private collections of manuals. And from what I have found indivduals like yourself, or Mr. Joel Gopan, are very willing to share this information.

Myself and many others thank you for this!

Ron

[dr deuce]

The ACKWX had a 256 engine in it. That is what drove the 270 design. The givmint wanted a little more omph. The Had the 270 in production in 19 days...!