The reason for making this upgrade is that AquaCraft has picked 3mm as a prop shaft size, the worst possible prop shaft size to fit aftermarket props to! In the USA we use 1/8" or 3/16" shaft size props. In Europe they use 4mm props. The good news is the rest of the shaft itself is 4mm wide.

This is a easy and inexpensive upgrade. All you need is a new 4mm prop shaft with a 4mm threaded prop shaft end.  This will allow you to run all the popular Graupner K Series or S series threaded props. Now please don't ask what size prop to run. I don't know. Each engine is a bit different so it may take a bigger or smaller prop to do the job. I can tell you that the stock prop measures 32mm in diameter, so that's a good starting point to build on. 

We start the install by removing the stock shaft. Place it next to the new shaft. Take note of the length of the old shaft and cut the new one a bit longer than the old. The reason I say this is because the threaded end of the new shaft may be a bit longer than the old one. Its better to cut and test the length and re-cut if needed, but impossible to make it longer if its cut to short.

Once its cut and installed to the length you would like your ready to install a new threaded prop. Thread the new prop on the shaft. You will notice that the Graupner threaded props are not threaded deep enough to thread all the way down to the drive dog that's on the shaft. So we need to  unthread the drive dog until it touches the back of the prop. Now remove the prop and loctite the drive dog so it doesn't move again. Re-install the prop and your done! All of about 30 minutes worth of work!

This is the finished product. With a much higher quality carbon fiber prop ready to make some waves!

Words of caution. Always remove glow plug before any work to the boat.