Lower pulley loosens on its own!

[tomarnold]

I flew my borrowed Fly Products 115 solo 210 motor, which is finally running properly! However, after flying for 5 minutes yesterday evening, the engine suddenly raced to high revs so I immediately cut power and landed. I found that the drive belt (a new one that I fitted yesterday morning) had slipped and become very very loose. 
I tightened it up again, but as soon as I revved the motor up a little it loosened right off. I tried this several times, but every time the belt would loosen. I'm not sure what I'm doing wrong, or perhaps a part is broken?
To adjust the belt I thought I had to loosen off the smaller nut that goes in parallel to the propshaft, then tighten the larger (17mm) nut that goes in to the back opposite lower pulley behind the prop. 

But is this incorrect? Can anybody suggest why this is happening? Very frustrating, as I am once again faced with a problem that has stopped my flying. Aaaargh!

Edited May 4, 2017 by tomarnold

[admin (Simon W)]

I have heard this happening if the bearings are grinding. (worn) so maybe worth giving that a check. 

Normally you can tell if you leave the prop on, and wiggle it at the tips (back and forth) you will feel some clunking / movement at the bearing. 

Good luck! 

SW

[tomarnold]

Thanks Simon. I assumed the bearings were ok as when I spin the prop without the belt on it spins freely and easily, but there does seem to be some play when wobbling the prop from the tips. It looks like I'll have to try and figure out how to change the bearings then...

[admin (Simon W)]

Any play is too much. 

I 'hope' this will solve it, it may not of course but at least you will have new bearings with no play!  

SW