Gearbox Rumbling

FlubbaBubba · Borekit Bruiser Joined: 01 Jan 2015 Karma :

Aprilia mx 125

The engine has just started whining/knocking. If you slip the clutch on pull of its bad but it only seems to be noisy when your on the throttle, its still there when you let of but its not to bad.

Cold start the noise is there and pulling the clutch in does nothing but the noise seems to get quieter as it warms up. If you rev it up in neutral its not to bad until you start riding it then it gets noisy.

All the gearbox, balance shaft and main bearings were replaced around 7000miles ago. Main bearings are koyo and the rest were skf.

The bike was also run with low gearbox oil for 3 weeks as one of the crank seals started to fail about a month ago. There was also a fair bit of swarf on the sump magnet.

Could it be a bearing on its way out?

Any help would be much appreciated, thanks.

Paulf · Nova Slayer Joined: 24 Jan 2017 Karma :

It sounds like it from what you say. Not heard the noise but if it is not there all the time it rules out the main and big end. Can you figure the likely candidate. If it purely a splash type gearbox they don't like low oil levels and can quickly go bad.

FlubbaBubba · Borekit Bruiser Joined: 01 Jan 2015 Karma :

Its a splash fed box which takes 600ml an 230ml was drained out when cold when it was low.

The noise seems to be there all the time but gets quieter when warm, it sounds more like a rumbling noise then knocking.

Im hoping its the balance shaft bearings and not the mains.

Thanks.

Paulf · Nova Slayer Joined: 24 Jan 2017 Karma :

Which bearing is the highest from the sump.would probably be the most likely candidate. Less oil to bathe in. But 230 mls seems low compared to 600 mls capacity probably accelerated wear caused by oil starvation. Good luck it looks like a gearbox rebuild.

Pete. · Super Spammer Joined: 22 Aug 2006 Karma :

Failed crank seals & rumbling in neutral = main bearings.
____________________
a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good Very Happy

Paulf · Nova Slayer Joined: 24 Jan 2017 Karma :

Sorry missed failed crank seal I concur with previous post could be connected. Has bearing fails it run eccentric and wears the seal out and then as it progresses as the balls or rollers become more worn it starts to rumble.

FlubbaBubba · Borekit Bruiser Joined: 01 Jan 2015 Karma :

Pulled the bottom end apart, there is no play in the crank on either side, and there is no play in the balance shaft or the gearbox shafts.

Got a second opinion on it and there saying its piston related as it gets worse under load a there seems to be a fair bit of vibration on the cylinder/head.

Paulf · Nova Slayer Joined: 24 Jan 2017 Karma :

Well in a way that's easier to sort.