Why is my MJ1200 with SureFlow mod doing this?

[mike31154]

Great, glad it's working for you... so far. Dunno about brilliant though, I'm not filthy rich, call it logical, although I don't have pointy ears, har har. Probably all the good training for my tech. career fixing aircraft instrument electrical systems. And yes, I did have the opportunity to work on some old prop jobs there, as well as the jets.

It was a long shot, but lucky I guess. I've never seen the Maxi Jet mod up close, but I tried to mod a couple of AquaClear power heads with propellers I purchased at hobby shops. The smaller ones seemed to work better, fkshiu's theory on mass of the larger prop has merit, I'm sure. When I fitted a prop to an AquaClear 802 and finally got it to spin in the right direction, the thing went nuts! So much power I could have emptied my tank in a few minutes with the water slopping over the rim!

Now with respect to the vibrating hum, I suspect that may be due to a slight imbalance and the fact that you're working with a longer shaft than the original design of the Maxi Jet. A minor misalignment of either the prop or the shaft will contribute to this excess vibration & noise. You almost need a secondary bearing farther up the shaft to minimize or eliminate any misalignment or flex. My fellow mechanical type techs had some pretty sophisticated equipment to balance props on aircraft & track rotors on helicopters. It doesn't take much to make equipment rotating at high speed self destruct. Even a few grams of difference can be huge and alignment is crucial as well. If it gets out of hand, or before it does, it might be worthwhile to ensure the prop is fitted as straight as possible on the shaft and that the shaft itself is not off at a slight angle. Then again, every time the prop hits the tab, it may mess up any effort you make to keep things straight.

Great mods for the money, but I'm glad I have my VorTech, it's designed with a prop in the first place and has a controllable DC motor, too bad the price is so hard to take. Wonder how the previous owner of the Maxi Jet dealt with the issue you experienced??

Live long and prosper.