Magic Pie Edge - How to replace mangled bearing cartridge in cassette?

[Benheron]

Hello All

I am a new owner of a Magic Pie Edge and (with the benefit of hindsight) made a big error by placing a home-made tubular spacer in my 8 speed cassette in an attempt to centre it in the frame (rather than using the inner nut on the axle, which seems to push it off-centre). It worked perfectly for a few weeks, then it started to click and crunch, and the result is a mangled the bearing cartridge inside the freehub. Hopefully the attached photos will show what I'm talking about.

So, my question is: how do I replace this? Is it a standard bearing set that I can buy from a bike shop, or do I need to order a new one from Golden Motor? Or do I need to replace the whole freehub unit??

Any advice would be much appreciated!

Ben

[Bikemad]

Hi Ben,
You should be able to replace just the inner and outer bearings on the freehub assembly.
The outer bearing on mine is a 6901Z (Z=metal shielded bearing) and the inner bearing is a 6902RS (RS= Rubber Seal) but I would be tempted to use a 6901 2RS on the outer bearing to help keep water and fine grit out of the bearing.

The bearings are readily available on eBay and here are the links:

• 6902 2RS 15mm x 28mm x 7mm inner bearing with 2 rubber seals
• 6901 2RS 12mm x 24mm x 6mm outer bearing with 2 rubber seals <----- I would fit this one in preference to the one below. 
• 6901Z      12mm x 24mm x 6mm outer bearing with metal shields

Here are some photos of my Magic Pie Edge:

The inside view of the R/H cover with the freehub unit fitted:


The complete freehub assembly:


The freehub outer bearing:


The freehub inner bearing:


And here is the inner bearing housing with the bearing removed:


It looks like it should be possible to remove both of the bearings from the freehub without having to remove the stator assembly (or unscrew the freehub from the side cover).
If you just remove the R/H side cover (complete with the freehub unit) you should have adequate access to replace both the inner and outer bearings.

To remove the cover, undo the nine allen bolts holding the Right Hand side cover in place and place a piece of tape on the cover in line with the valve to make sure it goes back in the same position.

Place a block of wood against the end of the axle on the controller end and give it a nice firm tap with a large hammer of mallet to separate the R/H cover from the hub. it is usually sealed with a silicone sealant, and it may require a fair bit of force (several large taps) to break the bond between the cover and the hub assembly.

Once the bond has been broken, the cover should slide off the axle with a bit of persistent pulling and wiggling on the cover/freehub unit.



Take care not to loose any of the spacer shims (thin washers) that may be fitted on the end of the axle, as they can sometimes stick to the inside edge of the inner freehub bearing.

I suggest that you also cover the exposed stator and magnets with a clean cloth to prevent any unwanted metal particles from finding their way into the hub. 

The old bearings will need to be drifted out of the freehub unit with a hammer and a suitable metal drift, but if you're really unlucky, they may have to be pulled out using a special slide hammer bearing puller:



If the freehub unit did need to be removed for replacement, you would have to remove the stator assembly and L/H side cover from the other side of the wheel, and then refit the R/H side cover to allow the freehub to be removed with a suitable 12mm Allen Key:



The allen key should be clamped securely in the jaws of a strong bench vice so that the entire wheel assembly can then be turned by hand to unscrew the wheel from the freehub unit:



If you need any further information or assistance, please don't be afraid to ask.

Alan
 

[Benheron]

Alan - you're a legend! Thank you so much. 

I have ordered the bearings so hopefully can work on this over xmas.

One question: when I bang the axle with a mallet, am I expecting the axle to actually move within the wheel? Or will it just be enough pressure to break the seal? The rest seems relatively straightforward (i think!)

I'll keep you posted on my progress...

Thanks again

Ben

[Bikemad]

Hi Ben,

The stator and axle are prevented from moving sideways by the two side covers, but when the side cover bolts are removed, the cover will still be held in place by the sealant around the outer flange.

During disassembly, the stator and axle assembly is basically used as a drift to force the cover away from the hubmotor's magnet ring.
When you apply enough force to the opposite end of the axle, the silicon sealant will hopefully be forced apart, allowing the cover to move sideways with the axle assembly.
Unfortunately, the very strong pull of the magnets will automatically pull the stator and axle back into the centre of the motor again.

So, to answer your question, the axle will "actually move within the wheel", but you probably won't notice it as it happens so fast, but you should hear a nice ringing sound from the cover when it finally breaks free.

If you thread a nut on the end of the axle so that the outer side of the nut is flush with the outer end of the axle, it gives a much lager area for the block of wood to press against.
If you use a large wooden, plastic or rubber mallet, then the block of wood is not required, it is only used to prevent damage to the metal axle from a metal hammer head.

I forgot to mention that the opposite end of the axle must not be resting against anything (e.g. the ground, a wall or your leg etc.) or it will absorb all of the impact instead of transmitting the force to the cover!

Alan
 

[Benheron]

Thank you Alan - that all makes sense.

I really appreciate your attention to detail and for taking the time to explain it all.

[UPDATE: I have fixed it! Your instructions worked perfectly and the bike is back on the road. Thank you again!]

Ben

[Bikemad]

Thanks for the update Ben, it's good to to know your bike is back in action again.
Alan