Deep down rattle!!!

[Emmett]

My dads monster makes a deep rattle noise when opened up under load. Anyone got an idea of what it might be? 10500 mile on the clock.

[Duncan]

'Pinking' by the description.

Most likely caused by either a weak mixture (pipes or air filter been changed?) preignition (get timing checked) or crappy low octane fuel (try Optimax instead)

[nik_the_brief]

Mine too, I'll be watching this thread closely.

Not sure if it's pinking on mine, is it possible that running it with the valves badly adjusted could have done some serious damage?

[gary tompkins]

'Pinking' by the description.

Most likely caused by either a weak mixture (pipes or air filter been changed?) preignition (get timing checked) or crappy low octane fuel (try Optimax instead)

A fair guess from Duncan. Other things that have been mentioned on the forum in the past are (1) piston slap (piston/bore wear or just wrong spec parts fitted), and (2) the flywheel nut coming undone causing a rattle.

(1) Maybe more noticable when the motor is cold?
(2) Very serious - as the flywheel can shear the woodruff key and trash the crankshaft.

More of a long shot is crank or small end wear, although it would be unusual at 10K miles unless oil & filter changes or level has been badly neglected.

[Rockhopper]

Which monster is it?

[Byron Kauffman]

Is this under load but at low revs like coming out of a slow corner? I asked the shop about this a while back and was told it was because the motor doesnt like to be lugged, keep the revs up and it is fine. I only ever have it happen at low revs where the bike labors under torque to pull itself along. It is a deep down slapping noise that sounds like the thing is coming apart and wants to toss parts up through the tank. Keep the revs up and it never happens.