The Stovebolt Site Forums The Shop Area Engine Shop Difference Between a Army & Civilian GMC 302

Howdy, anyone know the difference between a army and civilian GMC 302 cid inline 6 cylinder engine? I got asked this queston and have no clue :confused:

I believe that first off it was 24-volt, then the distributor is different(water tight?)I am not absolutely positive but I believe the basic block is the same

Luke's on the right track. The military version was modified to be driven in water. Had plugs for the breathers and an intake tube that could be used to pull air from the cab near the top of the dash. All of the electrical system was sealed, including the distributor and plugs. Ignition wires had screw connections on them. They also had a governer. It's been 30 years since I worked on one, but I was thinking they were designed to be driven with the engine completely submersed.

There's one in a salvage place up the road from me and it was sealed up watertight as mentioned, but instead of a dist. they said it had a magneto.

Cat,
I spent about a year converting a 302 out of a '52 GMC 6x6 and putting it in my '52 GMC 1/2ton.
There are several things that I had to do to make it work.
-The military 302 has side arm mounts on the front of the block held on with studs. These studs will work to hold the generator mount braket on the left side the others can be removed and bolts sealed in their place.
-You can either get a civilian timing cover plate from ANY other GMC 6cyl or drill two hole and use bolt as per original.
-The oval hole for the fuel pump has not been cut out and an electric pump is used. However, the camshaft does still have the lobe for the pump and the block has the provisions to cut out the hole.
-There is a mounting boss cast on the block in the way of where the civilian starter will mount and this needs to be ground off flush with the block surface. No one really knows why this was cast on the block but no harm is done by removing it. The starter for the military hydramatics used in these trucks mounts lower on the bellhousing along side the oil pan and the boss is not an issue.
-On the rear of the engine a different bellhousing is needed as well as a flywheel. These will bolt right on to the block and flywheel respectively. The crank is drilled for a six bolt pattern and the same "rare" 6 special bolts used for the hydramatic flexplate will work to secure the flywheel.
-The oil pan for the military configuration has an extra capacity extention added and extra tubing inside to get the oil pickup screen all the way to the bottom. An oil pan off ANY other GMC 6 cyl will be needed as well as the oil pump cover from ANY other GMC 6 cyl. The only thing to be careful about is that the pump cover used is matched to the capacity of the oil pan used. Some covers allow the pickup to sit farther down for the deeper pans. The pickup screen can be used from the military setup.
-A distributor from ANY other Chevy or GMC inline can be used. A hole will need to be drilled to hold down the vacuum advance.
The oil dip stick is mounted on the side of the oil pan in the militay setup. There is a boss cast on the block in the same location as on the civilian engines but it is not drilled. The hole needs to be drilled with a step in it. I can't remember the correct dimensions but e-mail me if needed and I will dig them up. The military dipstick tube needs to be cut and put into the drilled hole. The military dipstick can also be used.
-The water pump pulley will need to be changed. A water pump from ANY other GMC 6 cyl will work as a replacemant. The nice heavy duty 5 blade cooling fan can also be used on civilian GMC inlines and will bolt right to civilian water pump pulleys.
-The military crankshaft pulley dampener is the 7/8" two groove type and can be replaced with any dampener from ANY other GMC 6 cyl or even a 235 or 261.
-There is a cooling bypass line that is routed along the valve cover. This can be removed and the holes plugged. The military 302 also runs a compressor with extra cooling lines and oil lines going to the compressor these can be removed and the holes in the block plugged. Basically just configure the plumbing like any other civilian GMC inline and plug any holes left over.
-The military carb used is a sealed Holley two barrel. If the stock intake manifold is used, any 2 barrel downdraft carb will bolt right on. The exhaust manifolds are the same on military and civilian 302's.
These are great engines and lots are out in junkyards in old 6x6's.
Email if more info is needed.
Hope this helps.

52GMC6 has covered pretty much all the differences, I can only add that the blocks have different casting numbers (See Inliners) and all internals and cylinder heads are the same as civilian versions. Military blocks are rumored to be stronger castings but I've had both apart and side-by side, the only differences other than those mentioned above, are that the military block has some additional webbing where some of the accessories are mounted. The compressor mounts are great for supporting a power steering pump or A/C bracketry. And the double groove damper works fine if you move the radiator to the outside flange of the core support. Just be sure to use a water pump from a 270 to match the wide belt size. Some clearancing of damper pulley may be needed to clear the front engine mount if the pickup center mount is used.

Thanks for the help on this one guys, Your Great. I passed on the info to the guy asking and also sent hm a link to this posting.

THANKS