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What happen was my oil pump failed and a piece of it went in between crankshaft and cam gears and the gear turned on the crankshaft. So big problem, first I have to get the old gear off. This is what I was told and all I could find out. First cut the gear almost through to the crankshaft then use a chisel and hammer to split the gear. This does not work, I keep cutting closer and closer and I can tell you that gear is not going to split or spread enough to get it off. So I cut it 99% through on two sides and it finally broke off. Keep in mind this gear is put on with thermal expansion.
Replacing the Crankshaft Gear
This is something I did but I am sorry I did not make a video of it. If you look around you will find there is little or no information on how to replace the crankshaft gear on a cummins engine. First I will explain what I tried that did not work and how I got it to work.
At the end of this article I have the steps for replacing the crankshaft gear
It has been some time sense I did this so if I miss a step (sorry).

#1 You have to remove the support that the hood latches too.

#2 You have to remove the A/C coil (you will need new freon when it is put back on). Remove the turbo inter-cooler and radiator.

#3 Now you can get to everything, remove the fan, fan belt and crankshaft pulley.

#4 Remove the gear cover and valve cover. You don't have to worry about the engine being in TDC (top dead center) right now.
This is what is involved to replace the crankshaft gear on a 5.9 cummins.
What happen it went on about ½ and stopped so I took my wood and hammer hit it a couple of times and it went about ¼ inch more and stopped. So now it is ½ way on and is not going on or coming off. I am thinking I will have to buy another one and destroy this one. When the gear is all the way on you cant get behind it unless the crankshaft is out of the block. But ½ way on I thought I would give a gear puller a try. I have used gear pullers countless times in my life and this is the first time I had the bolts sheer off. So with new bolts in hand and a big pipe to go over my breaker bar I gave it another try. I got to the point to where something was going to break and stopped.
#5 Now we have to remove the cam gear, first thing to remove the cam gear is take the rocker arms off and push rods out. You will need 3/8 wood rod cut long enough to come out of the head about 1 foot or more. Tap with a hammer on end where you took the push rod out you will feel it go in the tappet. Pull up on one intake and one exhaust and hold them together with a wire tie. Repeat until they are all held up. Do not use rubber bands some people will tell you to do this, if fuel gets on the rubber band it will eat it up and break in about one hour. Remove the bolts in front of the cam. You can take the cam out now. You may have to wiggle and turn to get out. Remove the oil pump.

If you don't know what thermal expansion is, it is when one part is heated to make it big enough to fit over the other part so when they are the same temperature they almost become one. Or this is the scientific explanation, Metal expands when heated. Length, surface area and volume will increase with temperature. The scientific term for this is thermal expansion. The degree of thermal expansion varies with different types of metal. Thermal expansion occurs because heat increases the vibrations of the atoms in the metal. Accounting for thermal expansion is essential when designing metallic structures.
I set down with total discussed, then about 30 seconds later I hear a big bang. It moved but I could not tell it had move so I did it one more time and waited again a big bang so I keep doing this. It took about 1 hour to get it off but it came off. This time I left the gear in the oven 2 hours and took the gear out of the oven and used a oxygen acetylene torch and heated it up more. Using my welding gloves the gear slipped on with ease and went where it was supposed to go. So if the gear is hot enough it will go right on, if the gear dose not go right on with ease the gear is not hot enough. Stop and make it hotter or the gear will cool and stay where it is at.
#6 Next I used a air rotary tool but I guess you could use a electric. Buy 3-4 good quality deburring bits. I cut with the gear teeth so it would not be a straight cut but works. Cut as deep as you can with out hitting the crankshaft on 2 sides. Use a chisel and hammer it should break  in half now if not cut a little more and try again.

You can buy a new gear at Dodge or you can find them other places. You will need a key also, it looks like a steel pin. It only keeps the gear in the right place and does not hold anything. I could only find this key at the Dodge dealer. If you did not read (what I did wrong) you should read first I explain how to put it back on.

So I got the gear off now I need to put the new one back on. This is what I was told and all the info I could find and I have done this with small engines and it worked. WHAT NOT TO DO, take a toaster over set it next to your truck and turn the oven all the way up put the gear in side wait about one hour. Then use welding gloves and slide the gear on. If it does not go on tap on it with a block of wood and hammer.
One very important thing when putting back together is the oil pump. This gets installed wrong more often then you think and will fail if put in wrong. You have to make sure it is straight. It looks like it will fit in side the block but sits on top of the block. You should look at it before it is removed so you understand how it go's.
Step 1—Tighten to 8 N·m (71 in. lbs.) torque.
Step 2—Tighten to 24 N·m (18 ft. lbs.) torque.
3. The back plate on the pump seats against the bottom of the bore in the cylinder block. When the pump is correctly installed, the flange on the pump will not touch the cylinder block. I used locktite on the bolts. This calls for light torque. Do not try to do this by feel it needs to be torque correctly.

You can now put the cam back in. Take note of the marks on the crankshaft gear, cam gear and fuel injector pump gear you just have to line up the marks on the gears and the engine timing is set. I hope this helps if you have this problem.