It's popping the spring because there is a lip that the seal and bearing sit on, and the "step" between the two sizes of the crank isn't gradual enough. FIRST, check and make sure you didn't damage the seal. You may want to just get another one. If ok, you need to make something to let the seal glide up onto the step. You need something thin, and plastic preferably. I usually use a 20oz pop bottle. Take the wrapper off the bottle, then cut the ends off so it is just a hollow tube. (Like a paper towel roll.) Then, split it down the middle length wise. Wrap it around the crank, clear in where the seal goes and let it overlap. Mark it, cut the excess off, so that it only overlaps maybe 1/2". Lube it up with oil, then slide the seal up and over it. Drive your seal into the housing, then just pull the plastic out. If you have any questions, feel free to ask. I would have made you some pics, but I'm sitting in my bed on my laptop, and I'm too lazy to get up, LOL! Good luck!!
