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The once-dilapidated state of our Fuel Truck's GMC 270 straight-six engine before its restoration began. (photo via Mil-Spec Restoration)

Progress in December:

When last we visited our CCKW 353 Fuel Truck project, the big news involved the arrival of the vehicle's freshly-overhauled engine block from the machine shop. Mil-Spec Vehicle Restoration soon began the process of reassembling the components to put the engine back together again. They have made significant progress on this endeavor in the interim, as this report will reveal.

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The fuel truck's engine undergoing reassembly on its purpose-built, rotary stand at Mil-Spec Restoration. At this stage, the crank shaft and pistons have been installed, as has the cylinder head assembly (and its valves). The empty hole beside the crankshaft timing gear makes it clear that the cam shaft has yet to be installed. It is the cam shaft which drives the push-rods running up to the rocker assembly on the cylinder head that controls valve position. (photo via Mil-Spec Restoration)


After cleaning up the engine block for the Fuel Truck's GMC 270 straight-six engine following its arrival, Mil-Spec mounted it onto a purpose-built, rotary engine stand and began installing parts. (The image above shows the engine mid-way through its reassembly.)

Crank Shaft:

To begin with, the team washed the crankshaft to ensure it was free of debris. Rotating the engine block on its stand so that the bottom side faced upwards, they then carefully placed the crankshaft in position, laying the four journals against the newly-installed bearings (after first ensuring that the bearing lubricant holes had sufficient clearance). They then mounted the rear main seal and bearing caps, securing the crankshaft in position.

Oil Pump:

With the bottom side of the block exposed, the team then installed a New Old Stock oil pump, freshly-overhauled in their workshop. The oil pump sits within the engine block, protruding slightly into the crank case. The pump scavenges oil from the sump at the bottom of the engine, and forces it into a series of channels within the engine block itself. These, in turn, feed oil into the sets of bearings which secure the crank and cam shafts in place. This ensures that a proper supply of lubricant is applied to these critical interfaces. The pump itself is driven by a geared shaft (through the engine block exterior) which syncs up with the distributor.

Piston Assemblies:

With the oil pump and crank shaft installed, it was now time to rotate the engine block right side up again to slip each of the six piston assemblies into place (after having already lubed-up the cylinder walls). This just involves using a clamp to cinch-in a piston's compression rings, and then using a mallet to gently tap the piston into its cylinder, making sure to align the connecting rod's 'big end' with its appropriate place on the crank shaft before securing it with the end cap. Once each of the cylinders is attached to the crank shaft, it's then time to rotate the engine block again to apply the proper torque to two bolts securing each connecting rod to the crank shaft.

Cylinder Head:

With this accomplished, it was time to work on the cylinder head. This is the large metal forging which mounts on top of the engine block. It forms a tight seal against the top end of each piston, housing the intake and exhaust valves for each of them along with the mechanism for controlling valve position during the combustion cycle. The team lapped the valve seats to ensure a smooth seal with each of them, then cleaned the head to free it of any dirt particles. They also checked each of the valve springs to make sure they were in spec (they were) then installed them. Lastly the team disassembled the rocker assembly (which controls valve position) cleaning and inspecting the parts before then reassembling it all and securing it to the head. Then they mounted the cylinder head to the engine block.

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Another view of the fuel truck's engine undergoing reassembly at Mil-Spec Restoration. While the cam shaft appears to be in position (its end hidden behind the red cover) the push rods which run up the engine side to the rocker arms on the head remain uninstalled. (photo via Mil-Spec Restoration)