914 knocking

There are 6 different causes knocking vibration/ sound.

1. Bad Belt Tensions /Pulleys
2. Rod Knock: Worn Bearings
3. Detonation Knock: Bad Knock rubber joints
4. Detonation Knock: Lean Air/Fuel Mixture
5. Detonation Knock: Bad Timing/Trigger coil gap
6. Detonation Knock: Too Low Octane

The knocking sound often occurs when the air-fuel mixture is incorrect, which causes the fuel to burn in uneven pockets rather than uniform bursts.

you may check the detail is as,

https://www.rotax-owner.com/en/rotax-blog/item/57-vibration-help

Thanks, turns out it was the front wheel out of balance and out of round!

I use the Rotax 914 F2 engine on an unmanned aircraft. After take off (115hp) the aircraft declerated and crashed. affected parts on the engine are broken cylinder 4 piston, broken cylinder 1 exhaust valve. Fuel test conducted showed the octane number of mogas is 91. Is it possible that this fuel could be the cause of the engine knock?