50hp mariner replacing lower unit

[sibylernie]

I installed a water pump repair kit for my 50hp Mariner but had to remove and reinstalled the lower unit twice. The first removal to install repair kit and the second removal because I was unsure I had seated the copper tubing correctly in the pump. I have now removed the lower unit again because water was not comming out of the pee hole but was comming out of the upper back of the shaft housing. I think these are the exhaust holes. Anyway, I realized that the copper tubing may not have seated in the upper part of the drive shaft. Amoung other problems I found impeller parts in the upper seat for the copper tubing. I am now ready to reinstall the lower unit but it will not install. It stops with a clunk with about one inch yet to travel. Any suggestions?