The pin that holds the crankshaft fan belt pulley is coming out on my 19, What is supposed to hold that pin in place?
One or two cotter keys depending on the year. Look at the pin it should be drilled One side of the later type is drill for the pin to slip through the other is smaller so the pin will not go through. That is if you are running a Ford pulley.
The pulley should have 2 pin holes, one is larger than the other. The pin will not fit thru the small hole. Your pin should have a cotter key hole in one end of it. You will drive the pin thur the large hole in the pulley and thru the crankshaft hole. You drive the end of the pin without the cotter key hole in it, in first. After the pin is driven in and is about equal on both sides, you insert the cotter key into the pin. The cotter key will keep the pin from coming out the big hole and since the pin will not fit thru the small hole everything is supposed to be good. But the pin will need to fit tight and not be lose in the hole. The small hole in the pulley is just to use for driving the pin back out when removing it. This is for stock T parts, some aftermarket parts are different
If the pin is loose in your crankshaft, you might consider knurling the center of it. I've center punched that area too with similar results.
Another cure for a loose pin is to bend it in the middle a bit.