[Destroyer]

Originally Posted by 3 Squids

So I got the boat back today with a running motor!! Motor sounds great. I was talking to the motor guy and he believed the lower unit will be fine. He said it appears someone used the wrong type of nut on the prop shaft and the threads have minor damage to them. He told me to bolt the prop on if it torqued down properly and didn't strip any thread I'd most likely be fine. He also suggested using a cotter nut and drilling a small hole through the shaft for a cotter pin. But mechanically all seems well the the lower unit.

Before you go and start drilling holes do like a professional machinist would do. Get yourself a couple of thread files. They come two different ways.. one is just a single "V" shape that you place in the grove of the good threads and work backwards towards the damaged threads (useful for a quick touch-up where one thread goes over the next). The other is a long square bar about 9" in length. Each end has 4 different thread sizes ground into it, one ground into each side, for a total of 8 different thread sizes per bar. Buy the bar that has the threads you need on it, lay the correct side of the bar in the good groves like the previous file and work your way from good threads to the bad threads, filing away the damaged parts of the thread as you go. The advantage of this type of file is that since you always have a few teeth ( VVVVVVV) in the good threads your chances of success with restoring your shaft are greatly increased. Most places that sell industrial and machine shop tools will carry them. Harbor Freight even has some, that, although not the best quality, should do the trick as long as the threads marked on the bar match the ones on your shaft. Be aware that they come in both SAE and Metric, so choose carefully. You'll need to know the diameter and how many threads per inch (TPI) your shaft has.