grinding at 5000rpm

n.sack · L Plate Warrior Joined: 17 Mar 2015 Karma :

My hyosung cruise 2 makes a loud grinding/vibration noise at 5000rpm but disappears as soon as it hits 6000. It definately isn't the drive chain or any loose bolts or anything rubbing on the exterior and I'm positive its coming from the engine. It does it when riding in any gear, in neutral and any gear with the clutch in so basically all the time. Anyone know what it might be?

Rogerborg · nimbA Joined: 26 Oct 2010 Karma :

Not a clue. Top or bottom end? If you're not sure, eBay yourself a stethoscope, or get a piece of wood, hold it against the engine in various places and feel for vibrations. If you want to get properly zen, hold it in your teeth. This is less trollish than it may appear.
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Taught2BCauti... · World Chat Champion Joined: 12 Jan 2012 Karma :

Could be the timing chain. If it is slack or worn, it could do that.
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Nemo · Could Be A Chat Bot Joined: 30 Apr 2010 Karma :

Resonance
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cheeseman · Trackday Trickster Joined: 11 Jun 2014 Karma :

As Nemo said, it could be just that your hitting a natural resonant frequency when it's at 5000rpm and something is vibrating strongly along with it causing it to sound like a grinding noise. Either that or your engine is about to explode. No idea really. Can you record it and put it on youtube?
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