Strange knocking sound from Magic Pie 2

[OldAndTired]

Hi

I bought a Magic pie 2 a couple of years back. I have not done too much riding around 500-600km all up.

My motor is now making a strange knocking sound.
I took it to the bike mechanic and they rode/ tested my bike, and they said the sound is definitely coming from the Hub motor.

I have uploaded 3 videos capturing the knocking sound (please forgive shaky video) its not a regular sound but rather occurs randomly.

Can anyone please give me some advice. Note I have not modified or ever opened up this motor, so it’s as delivered.

http://1drv.ms/1JkGE07

Any help is much appreciated
Andrea

[Bikemad]

Hi Andrea andto the forum.

Did the noise start faintly and slowly become progressively worse, or did it start all of a sudden after the bike had been left unused for some time?

It sounds to me like something is slightly touching against the stator but the strange thing is that it doesn't appear to be happening in the same position relative to the wheel rotation.
If it has not been used for some time and has been stored in damp or humid conditions, it is possible that some surface rust may have built up around the edge of the steel laminated stator, which could be catching against something as the hub rotates.
If this is the case, it should hopefully improve with further use without the need to dismantle the motor.

Excessive play in the wheel bearings can also allow clearance between the motor ring and the stator to be reduced, which could also result in the stator touching against moving hub parts.

Give the wheel a good push, pull and wriggle in various directions to see if you can reproduce the noise and also check for any signs of the following movement in the bearings:



The noise I was listening to on the video is very similar to the clonk that the rear freewheel makes as it takes up the slack when turned quickly by hand. The noise is amplified by the large side casing which produces the "hollow sounding" knock. It is possible that a faulty wheel bearing could radiate a similar sound though the side casing too.

I might also be worth checking the tension of the spokes by pinging and gently flexing each one in turn to make sure they are all still nice and tight, as a loose spoke can sometimes make clicking noises too, especially if the nipple comes unscrewed completely and and starts rolling around inside the hollow cavity of the rim section. 

Alan
 

[OldAndTired]

Hi Alan

Thank you so much for the prompt response.
Answers to the questions in red:

Did the noise start faintly and slowly become progressively worse, or did it start all of a sudden after the bike had been left unused for some time?
As far as I remember it started all of a sudden - and at the same sound level, i.e. the noise did not start faintly

It sounds to me like something is slightly touching against the stator but the strange thing is that it doesn't appear to be happening in the same position relative to the wheel rotation.
If it has not been used for some time and has been stored in damp or humid conditions, it is possible that some surface rust may have built up around the edge of the steel laminated stator, which could be catching against something as the hub rotates.
The longest period between uses has been around 6-8 weeks, the bike has always been housed in the garage. I am in Brisbane Australia so it does get hot and humid.

I might also be worth checking the tension of the spokes by pinging and gently flexing each one in turn to make sure they are all still nice and tight.
I checked the spokes and they are all nice and tight.

Excessive play in the wheel bearings can also allow clearance between the motor ring and the stator to be reduced, which could also result in the stator touching against moving hub parts.
Give the wheel a good push, pull and wriggle in various directions to see if you can reproduce the noise and also check for any signs of the following movement in the bearings:

This is where it gets interesting, and I think you are spot on Alan.  I shook the wheel and it sounded like there was something loose in the hub, then the sound seemed to diminish / disappeared. I then moved the wheel forward slightly and shook again and the sound returned. Again i'm not sure if this is the normal sound of a hub motor, as I never shook it when I first received it, so i'm assuming its due to some sort of wear and tear. I have added a video of the wheel shake aptly named: Wheel_Shake.avi  :-)   

Video location here:

http://1drv.ms/1JkGE07 

I tried also pushing pulling wheel, but the sound only occurred with the shaking as above video.

thanks again for your time and effort, any advice / recommendation gladly welcome.

thanks

Andrea

[Bikemad]

Hi Andrea,

The rattling noise does not sound very nice at all. It sounds like something very heavy and solid is moving inside the hub in relation to the axle and side covers, and the only heavy item in there is the Stator which should not move at all, as it supposed to be a tight press fit onto the axle:



Unfortunately, the wheel needs to come off and be dismantled to find out where the movement is.
Hopefully you will be able to see what the problem is by just removing the right hand side cover.



If not, remove the whole stator assembly for a closer inspection:



Alan
 

[OldAndTired]

Hi Alan

Thanks for that, I will have a look this weekend at opening up the motor (work is flat out at the moment - so don't get too much of a chance during the week  )

will post pics / videos of my finds.

thanks again for all the assistance.

Andrea

[OldAndTired]

Hi Alan

Managed to get some time and got the cover off. There appears to be a wobble in the stator see videos: GM_motorWobble_1.avi and GM_motorWobble_2.avi
located same spot: http://1drv.ms/1JkGE07

Now I have not removed the stator yet as i'm not sure what extra information it will give me.
Let me know your thoughts, and I can try get the stator off.

thanks

Andrea

[Bikemad]

Hi Andrea,

The wobble movement appears to be movement in the bearing between the axle and the side cover, not between the axle and the stator as I had expected.

This means that the movement should have been detectable when the wheel was assembled and bolted in the forks.

The solid clonk I heard originally might be due to lateral movement of the stator and axle assembly in relation to the hub as indicated by C in the following picture:



In which case it should be possible to add some thicker or additional shims (washers) on the axle before the cover bolts back on to remove the lateral movement by slightly preloading the bearings.

Replacing the two hub bearing should improve the wobble movement but I am not convinced that this was causing the original clonking noise, and the slight bearing play should not be a problem if spacer washers are used to remove it.

If you can't find any suitable steel spacer washers, try a suitable rubber "O" ring or even cutting some spacer washers from cardboard and reassembling the wheel to see if it reduces (or completely eliminates) the clonk.

Alan
 

[OldAndTired]

Hi Alan

An update of current work.
I tried looking at taking off the left side cover of the hub motor, as I thought I could try adding a washer on either side to even it out, but due to a clip within the recess (photo provided) I could not open this left side and pull the cover off.

So the next thought was just adding an extra washer on "the right side" of the hub motor. there is currently an existing washer (photos provided) which will push against the smaller bearing ring (photo provided).

As you mentioned, I tried a cardboard washer (photos provided) to see if the added depth would hold the stator more tightly, I reconnected the right hub cover, and did a test shake (video provided) and there was no knocking...

Excellent I thought, so just to confirm I re-opened the right hub cover and removed the cardboard washer and reconnected the hub cover and re-did the shake test, and...

no knocking sound (I did not bother with the video as it was identical to the cardboard washer shake test).

So I thought it must have been the wheel installation which somehow caused the knocking.
So I re-installed the wheel / torque bars etc and re-did the shake test (video included)and the knocking has magically disappeared (Note there is some rattling- but that was from the brakes).

So I'm at a lost, will go for a ride on the weekend and see how it goes. But for now it appears to be working.... 

i will give you an update on the weekend.

thanks again for all your assistance and useful information.

Andrea
pics/videos usual spot: http://1drv.ms/1JkGE07

[OldAndTired]

Hi Alan

So I tested the bike today, and after about a km the sound came back.
I was doing slow left and right tight turns (like an S shape) and I noticed the sound occurred mainly when I was turning left (not sure if that has any significance)

So I bought some new tools and managed to get the left hand side cover off.
the bearing remained on the axle, so I was thinking of putting a rubber washer within the left hand side cover recess, so that the bearing can be preloaded, and similarly a washer on the other side (ie replace the cardboard washer(as per pic) with a metal washer)

Is this the correct course of action?
is a rubber washer OK or should I place a metal washer on both sides?

Thanks

Andrea
pics/videos usual spot: http://1drv.ms/1JkGE07 (Apologies for the noise, but it was pouring rain and I was in my shed)

[Bikemad]

Hi Andrea,

I would suggest cutting a 42mm diameter cardboard disc with a 25-30mm hole on the inside and then cut a slit on one side to allow it to pass over the cable and fit inside the cover before the bearing goes back into the recess.

As your cardboard appears to be quite thin, it might also be worth putting two cardboard washers inside the recess instead of just one. 

Alan
 

[OldAndTired]

Hi Alan

I managed to find a steel washer for the right hand side, and a couple of fiber washers for the left hand side.

installed the washers and covers, then re-assembled the wheel.
took it for a quick ride as it was dark out, but so far so good...  no knocking sound... 


Thank you so much for you advice and patience.

Andrea

[Bikemad]

Took it for a quick ride as it was dark out, but so far so good...  no knocking sound... 

Let's hope it stays that way (the knocking sound, not the darkness).



Alan