CCKW Engine casting & forging numbers

[RANGER]

Be careful, there are some charts available on the internet that are misleading as to GMC block casting numbers and forging numbers. There are enough errors on the one called "GMC-The numbers Game" that will cause much confusion and create problems. Avoid using it as it is very misleading to those without years of GMC 270 engine experience. It is not written so as to relate to WWII era numbers as used on the 270 engine. It is very inaccurate in its description of Rod Forging 2135419, and will cause expensive mistakes by owners trying to use the chart.

[RANGER]

I'll just give one example to illustrate the confusion that can happen.
There are two versions of Connecting Rods with Forging Numbers 2135419, the one used for the WWII 270 uses the WIDE Connecting Rod Insert 1.212" and is machined for a wide locking tab to lock it in place.

The 2135419 Connecting Rod for the early 1950s 302 as used in the M-Series used the NARROW Connecting Rod Insert, 1.107" and is machined with a NARROWER relief for the NARROWER Locking Tab on the NARROWER Connecting Rod Insert as used in the early 302.

What happens quite often is that inexperienced mechanics install the NARROW 302 Connecting Rod Insert in the EARLIER WWII CCKW 2135419 Connecting Rod, the Insert Bearing will not be securly locked in place as the locking tab is too narrow for the relief in the WWII CCKW Connecting Rod.

There were several Crankshafts to contend with over the range of the 1941-1960s Crankshafts and 3 or 4 different Connecting Rods that all took different bearings, the later Rods with the 1.050 pin had different offsets at the Crankshaft.

This turns into a nightmare for the novice mechanic when he visits a modern day partsman at NAPA, Carquest, etc. The Counterman scratches his head in confusion, the buyer is not worried as he is clueless to the variations, wrong parts are ordered, the owner attempts to bring back dirty bearings that do not fit, etc. It turns into a nightmare.
That was just an example.
The process of preparing later blocks for the CCKW is best left to experienced machine shops.

We have already seen what happens when a correct appearing 256 block is fitted with 270 parts. It ends up with a lot of finger pointing and no solution to the time and money wasted.
If you do want to upgrade, take the old and new engines to a reputable machine shop to sort out.

[RANGER]

Don't let the 270 confuse you, there are experts that can build up a perfect 270 and save you mistakes, Bob Rubino at Mil Spec. is good at it. Experienced automotive machinists that have worked on the 40s engines are another, my friend Joel Gopan can help with finding correct parts, his CCKW is testimony to that.