AK550 slight howl

[randyo]

I got 27xx miles on my AK now, so I will be bringing to my dealer for 3k service shortly. I went for a ride yesterday, first in several weeks

I could hear a howl that changed pitch with speed, not a wind howl, cause it changed with engine speed, but only under maintenance throttle, it wasn't there under acceleration or deceleration

I can hear it barely with my helmet on, and if I wore earplugs like a lot of riders, I wouldn't have heard it at all

Thoughts?   at first I thought I might have a bearing going, but I am not familiar with cvt transmissions and what goes on inside them

[CROSSBOLT]

I vote gears and cam chain. Assuming the CVT is scaled up from the 300i machines (which are scaled up from the 50's!) the super slim roller bearing in the clutch is the howler when dry of lube but only when stopped with engine running.

The other thing could be the cooling impeller for the CVT. That thing moves a surprising amount of air!

[randyo]

I vote gears and cam chain. Assuming the CVT is scaled up from the 300i machines (which are scaled up from the 50's!) the super slim roller bearing in the clutch is the howler when dry of lube but only when stopped with engine running.

The other thing could be the cooling impeller for the CVT. That thing moves a surprising amount of air!

no noise when stopped with engine running, no noise while accelerating, no noise while decelerating

only when giving enuf throttle to maintain speed, and mostly speeds between 25- 50, not any cam chain noise I ever heard

[rjs987]

Where does your final drive belt sit on the rear sprocket?
I wonder if it is possibly rubbing on the side of the belt?

[Ruffus]

@randyo, I don't think with this mileage could be something really serious.

Since your scooters technical set up (CVT and tranny) is completely different (pls see pic) from our common "bread n' butter" scoots it's very hard to do an remote prognosis. There can be a lot of sources.

Only a skilled tech with some experience and the will to hear something would be able to make a judgement.

Maybe have a look..
https://www.easyboost.fr/en/blog/how-to-disassemble-or-change-variator-belt-rollers-of-the-kymco-ak-550-n9

[CROSSBOLT]

@randyo, I don't think with this mileage could be something really serious.

Since your scooters technical set up (CVT and tranny) is completely different (pls see pic) from our common "bread n' butter" scoots it's very hard to do an remote prognosis. There can be a lot of sources.

Only a skilled tech with some experience and the will to hear something would be able to make a judgement.

Maybe have a look..
https://www.easyboost.fr/en/blog/how-to-disassemble-or-change-variator-belt-rollers-of-the-kymco-ak-550-n9

Looky all those STRAIGHT CUT GEARS! I wonder if that is the noise source....?

[rjs987]

Looky all those STRAIGHT CUT GEARS! I wonder if that is the noise source....?

Could be. The ST1300 and CTX1300 (same engine and transmission) have square cut gears and make a very distinctive sound that many owners have come to love. Some call them the Singer Sewing machine sound or Jetson space car sound. But it is unique among motorcycle engines.

[randyo]

Looky all those STRAIGHT CUT GEARS! I wonder if that is the noise source....?

likely, as I said only a "slight" howl, not getting louder, and only detectable under maintenance throttle

[jimy.j]

Has anyone identified the cause of this sound? I have the same problem which is getting worse. So far it seems to be some sort of bearing in the transmission?