FIXED Cromotor v2 RUB, MAGNETS came UNGLUED!

[Tench]

I have seen an X5 that looked to have worse cracks but I don't think they were cracks, I thought they were just poor quality casting. As your marks appear to go to the bearing hole can you see if they are visible on the machined face, if not I suspect they are just casting marks, if you can see them on the machined face then yes they will be cracks, if you cant see them I would be happy to conclude they are not.

But even if they are they would not allow enough movement to cause rubbing. that could only be caused by:
1, a failed bearing or worn/loose bearing housing
2, ovality in the stator or magnet ring
3, a bent axle, can you mount it between centres and rotate?
4, the magnets have been slipping and now are sitting too high because of accumulated muck behind them?

 

[John in CR]

That's more than hairline stress fractures from pressing bearings and getting the cover seated. That cover is toast and is putting the stator off center, though bad bearing could be helping the problem seem worse. As the stator expands when hot it rubs more, but soon it will simply grind all the time. The problem will get progressively worse and ruin the magnets if it hasn't damaged them all ready. I wouldn't ride in the meantime. I doubt you can even get it back on without far worse damage to the cracked parts putting the side load while pressing the bearing in or pressing it on the axle, or just the act of seating the cover.

You might be able to buy some time welding or epoxying on reinforcing plates on one or both sides....no guarantee that you get it right with a perfectly centered bearing cup though.

You'll want to change both bearing while it's open. The wire side cover looks fine.

 

[Offroader]

bent axle, how could I check this?

I'll tell you it was very difficult getting the motor out of the dropouts. It took me a long time with a orange mallet of whacking hundreds of times. I had to slowly wiggle it out by whacking the tire laterally, and even had to whack the axle a bunch of times on one side.

I don't know why it was so hard to get out, maybe the clamping dropouts squeezed the metal more tightly to the axle is what I thought.

Could that be a sign of a bent axle? If bent it must be ever so slightly bent. Would that cause the problem?

Look at this stress crack, seems to have run the whole side of the case.

 

[Drunkskunk]

Those cracks look like it was cast too cold, and are just flaws in the casting. They may or may not ever be an issue. However, the inside of that bearing hole looks like you had a spun bearing. Is that bearing seized or dragging? does the whole measure out to be oval or too large?

 

[Offroader]

Could anyone recommend or send me a link to where to buy new bearings for this motor?

I thought the bearing seat looked oval at first, then the bearing also looked oval. However, I took a caliper and twisted it inside the jaws and it measured straight all around. Weird, so I think it is round now. Although, it looks very slightly oval to me.

 

[Ohbse]

What are the bearings like? Without seeing in person I can't say for certain, but my guess is that those side cover cracks are actually not overly structural. The casting is not amazing but should still be more than strong enough. If your bearing has partially seized and spun in its seat this could actually flog out the side cover clearances enough that the stator would be contacting the magnets, that should be pretty obvious though as the bearings would be farked.

How difficult was the side cover to pull off?

If the damage is limited to bearings then it's potentially not too difficult to fix, however if the area in the covers that the bearings are seated is damaged then it's much harder.

 

[Hugechainring]

OK, so now there is something to go on.

There are no easy ways to check some of these parts, because you are looking for errors in the thousandths of an inch range. It is much easier if you have access to someone with a machine shop that is favorable to your cause. In the case of the bearing housing bore, it may be so bad now that it is obvious.

1) You can check the bore in the side cover by removing the corresponding bearing from the shaft and using it as a gage. It should be a light press fit with no gaps That means if you need a few light blows with your orange hammer and a piece of bar stock as a driver to install it, it's OK. If it just drops in, no good. If it came off very easily after you broke the seal around the bolt holes while taking it apart, it's probably no good. Off center problems cannot be determined readily without a dial indicator.

If it was me I would perform this check after removing the bolts and the freewheel adapter. It will be easier to see if those "cracks" are opening up. Those side covers are not very thick to begin with and after they machine off the excess material, the bearing bore is not nearly as stout as it was before. If you remove the freewheel adapter, you'll see what I mean.
As far as the cracks go, you can pool a little solvent in the areas where the "cracks" are. Wait a bit. If you lift the cover up and look underneath, the solvent will seep through and you should be able to see it.

2) The axles are pretty stout, but your bike is on the heavy side as I recall. It is most likely that any bending would occur between the shoulder where the threads end and the end of the axle. This won't cause the problems you are seeing.

I'm speculating that there was probably more than one contributing factor. Regardless you just want to fix it. I would contact whoever you purchased your motor from, and politely explain what has happened, and send them a few photos. They can contact the factory on your behalf. If you are fortunate, they may just send you out a new side cover.

The advice about new bearings is well founded. Size matters :wink: , in this case, but more importantly is the class of fit. Bearings come in all different fit classes and preloads for different purposes. A bearing used in a laundry cart wheel is pretty sloppy and only good for low speed, while bearings for machine spindles are extremely accurate. Both can have the same nominal dimensions, but one costs $3 and the other $100. Really what you want are bearings designated as EMQ, which stands for Electric Motor Quality. Most of the Chinese bearings with this designation are a good value and OK to use. If your piggy bank is overflowing you can buy SKF, Nachi, NTN, or something similar. I don't know why one of those bearings is shielded vs sealed. Probably cheaper. I would replace both bearings with EMQ sealed versions. They are usually designated as 2RS, meaning 2 rubber seals. When the motor heats up, the seals will help keep the grease in. Speaking of that, the better bearings come with...wait for it... better grease. I have found some good Chinese bearings that are manufactured with high quality name brand lubricants.

At least it looks like a non-winding problem. While you are waiting you can go around and remove all the magnetic dust. I use an air gun to blow the dust over to a place where I can get to it, then remove it with the sticky side of duct tape or something similar.

 

[gogo]

I haven't had to change bearings, but what would the proper method?

I'd assume you'd want to heat the side cover and press in the chilled bearing by applying force to its outer race. Then chill the axle and press the heated bearing/cover by applying force to only the inner race and not by pressing on the side cover.

If a previous owner caused pressing force to be transferred from one race to the other, thereby denting the ball bearings, it might cause enough damage to fark the bearing up. I can't see how the bearings wouldn't have to be replaced every time a side cover was removed.

 

[Offroader]

I must admit that figuring out this problem seems to be a bit overwhelming.

I'm starting to question about putting more money into this motor.

The stator is rubbing now even when it is not heated. There must be a more scientific way to measure and find out exactly where the tolerances are off. The wear marks on the magnets seem to be worn evenly which tells me it is not one side tilted.

I have a milling machine with various dial indicators. There must be a way to measure everything and see if something is off.

The bearing looks fine from inspection. It seems I would have to push with force to get it into the bearing seat.

I don't know if this is possible, but maybe I can drill a hole where the magnets meet the stator so that I can visually inspect how and when it is rubbing when everything is closed up. Would this be a good idea?

Basically, I need a more scientific approach to measure everything, as that is the only way I think I'm going to find what is out of alignment.

 

[Ohbse]

How do the bearings feel?

Remove bearing from the axle, press into the side cover. Use your finger as an axle and spin the cover. Any vibrations? High spots? lateral movement? How long does the cover take to spin down? Can you deflect the inner race compared to the outer race?

To give you an idea, the cover from my HS3540 when spun on my finger would spin with no detectable vibration or grinding for quite some time, 30 seconds+

 

[johnrobholmes]

How fast are you hitting the stairs? Why has nobody mentioned that you bent your motor going up stairs, and then continued to ride it (damage it) for three more weeks before opening it up and finding the damage ?

You probably bent a side cover, and then continued to ride a wonky motor until the problem MADE you stop riding it.

 

[Offroader]

How fast are you hitting the stairs? Why has nobody mentioned that you bent your motor going up stairs, and then continued to ride it (damage it) for three more weeks before opening it up and finding the damage ?

You probably bent a side cover, and then continued to ride a wonky motor until the problem MADE you stop riding it.

Well, going up the stairs causes the motor to overheat greatly, which gave me the first sign of trouble. I don't have any proof if I actually cracked / bent anything, other than those hairline crack marks inside the cover.

Yes, I have put this cromotor through a lot, lots of stair riding, both up and down, lots of jumps about 2 to 3 feet, lots of hitting curbs. I guess the cromotor can't take this kind of riding? I do have full suspension with around 8-10" of rear travel but I had too light of a spring so I bottomed the suspension out a lot.

I do wonder how much abuse a hubmotor can take. It would seem that the side covers would be the first too break and that seems to be the case with those crack marks.

I'm surprised a lot of you are thinking all those crack marks are normal. One side doesn't have any at all, and the other side has so many of them.

 

[Hugechainring]

Here's an idea. Disassemble the side cover from the rotor. It should be a tight fit. You should need to install the bolts in order to pull it together. if it has a loose fit, it's no good. Do a careful visual inspection on the lip on the outside flange of the side cover. Look for signs of cracks or deformation, like if it has shifted one way or another. Any problems here, the side cover needs replacement.

If you want to check, here is a procedure for sweeping the side cover.

1) Take the side cover off the rotor. There is no way this will work with all those magnets near the indicator.

2) Mount the side cover to the machine table with the inside facing up. This is harder than it sounds, because you can't obstruct the bores. I would suggest removing the freewheel adapter as I mentioned, then use the open bolt holes to attach the side cover to the table. The flange face needs to be pretty square to the table.

3) Put your test indicator in the spindle. sweep the bearing bore, moving the table around until there is virtually no run-out. The reading you get when no table movement will improve the centering is how out-of-round your bore is. Once you get here, lock the table.

4) Raise the spindle, then sweep the indicator around the male lip on the flange that presses into the rotor. You can switch the indicator if you need to, doesn't matter. Just don't move the table.

The Total Indicated Run-out (TIR) (high to low) is what is read off the indicator at this point. One half of the total is how far off center the bore is from the rotor locating lip. Take readings at 12:00, 3:00, 6:00 and 9:00

Simplified example:

12:00 +0.005" 3:00 +0.003"
6:00 -0.005" 9:00 -0.003"

This means the lip is .005 off center (0.010 TIR) at 12:00, .003" (.006 TIR) off center at 3:00, and .002 out of round ( .005 -.003)

You can check the axle if you have a lathe or bench centers, but it takes some experience and some setup that is difficult to explain. If you can press the axle out, you could take it to a shop, and they could check it for you in about 10 minutes. Or, you could send it to Tench. I know he would be interested, and if it's jacked he could make you a new, high strength version.

All that new info regarding your bike and riding style is important.

Since the magnets are hitting all the way around, either the bearing is trash, the axle is bent, or both. If the side cover bore is off center, the magnets would more likely hit only partway around. The side cover could still be damaged or out of spec.

I would encourage you to fix the motor. It's a really good motor, and I can't think of a stronger, lighter more durable substitute. Fix your suspension, and maybe rethink your riding habits. The stress created when the springs no longer do their job can become enormous. At least you still have the bump rubber, otherwise you would have probably blown out your shock by now.

 

[Spicerack]

I would almost bet on the axle being bent. Lots of jumping and stairs... it should be able to take it but maybe it can't.

Not sure about the cracks in the cover- they could be imperfections from the casting process- they sure look ugly.

Another clue is that the wheel was very difficult to remove from the dropouts- this again suggests a bent axle. To test that you'll need a dial gauge setup...

Is the rubbing on the stator laminations only in one area- maybe toward the top as it is mounted in the bike? That would make sense if the axle has bent with the centre section flexing upwards.

Good luck!

 

[Ykick]

2'-3' jumps? These things are around 20-25lbs? Holy shit, something's most likely gonna be bent IMO.

I believe those "cracks" are merely surface fissures and probably don't go deep enough to compromise structural integrity. Dig into one with a sharp tool or junk grinder wheel and look under a magnifying glass to see if they're deep cracks or merely on the surface.

 

[crea2k]

You can always get an engineering company to weld those cracks up for not a lot of money, that way they wont develop into anything further if they do go deeper.

 

[e-beach]

How about this for checking the axle (and maybe the bearings.) Slide the bearing onto the axle and into place. Suspend the stator on the bearings upon two blocks of equal height with a narrow gap below the stator and a surface. Slowly spin the stator and measure any up and down movement of the stator. If there is none, your axle is fine. If there is up and down movement, your axle is bent. Maybe it can be done without the bearings....?

 

[johnrobholmes]

The side covers are made from junk pot metal. You may have a bent axle, but you also need new side covers. I agree that the motor is worth fixing. I would get new side covers made from 7075 T6 or 4340 chromo, if it were me. Not sure what the guys in Croatia are making the axles out of, but 4340 should really be the first choice of material and not some soft stainless grade.

 

[Offroader]

Thanks guys for the input, I will be measuring everything based on your advice as soon as I can.

I looked at the dropouts more closely on my bike and measured them also. One of the dropouts must have pinched tighter because of the clamping, so instead of around 10.1mm it gets narrow where it clamped to about 9.7mm. I can see that it looks pinched and narrows down.

That is the reason why I couldn't get the motor out easily, doesn't hint towards the axle being bent.

Now I have to figure out how to open that dropout a bit to get the axle back in easily.

 

[Offroader]

One other thought, is it possible that the round piece that the magnets are in and also have the spoke holes, could this possibly be bent? Would over tightening of the spokes actually cause this to bend, or is this piece too strong to bend before other parts bend.

 

[Hugechainring]

Unlikely.

In addition, picture the new shape in your mind. It's now oval, or egg shaped. The contact on the magnets would be only on the narrow spots. You have contact all the way around.

e-beach has a really good idea. What he has drawn up would tell you a lot. If you have V-blocks, use those under the bearings. Or, since you have a mill, you could whip something up.

So it goes like this. Clamp the stator assembly with bearings to the mill table using the blocks shown in the example. Mount an indicator and sweep the OD of the laminations while spinning the stator on it's own bearings. I would be looking for .005" or less TIR. Any wobbling from side to side is suspect as well.

 

[Ohbse]

I'm surprised a lot of you are thinking all those crack marks are normal. One side doesn't have any at all, and the other side has so many of them.

That's precisely why I suspect that the cracks aren't all that serious and probably aren't contributing to your clearance issues. That type of cracking is not unusual if you spend any time looking at other non appearance critical castings like gearbox bellhousings etc. If you're really worried about the cracks (assuming the cover checks out as dimensionally accurate) you could use a die grinder to open them up a small amount and have somebody proficient with a TIG weld them up. Personally I wouldn't bother.

You still haven't answered the questions about the most likely culprit that's the easiest to check and easiest to replace item - what are the bearings like?

That said if you've been jumping stairs it seems likely to be axle related.

 

[Offroader]

I removed the bearing on the freewheel side and to me it looks and feels fine. I put it in a measuring caliper and rotated it inside and it was round. The other bearing is still in the case. They both are very smooth and feel stiff with no flex.

Visually I can not notice anything wrong with the motor, but I am only dealing with 1-3mm of clearance to cause rubbing.
This is a very small number and will probably take precision measurement to actually find what is bent.

One other thing I did was I must have bent my rear rim somehow and this caused a bad hop. I was not able to true the tire radially to remove the hop and drove the bike like this for a while now. It was bad enough to shake me while riding, I also didn't have the wheel laterally trued very well also. I wonder if this vibration could have done anything to the motor.

 

[Tench]

We can see from the pics that the magnets are scraped all the way around the mag ring but we cant see all of the stator laminations, have these rubbed all the way around too or only in one place?

Rubbed on the lams in one place and all around the magnets would suggest a bent axle. as I mentioned in my previous post, put it between centres and rotate it to see if it is true or as was suggested with an explanitary pic sit it on the bearings and rotate it, either way should show you straight away if this is where the problem lies.

The axle has centre locations machined into the ends that would have been used during manufacture, using these should hold it perfectly true but could also show up bends outside of the bearings that would not cause an internal problem, running on the bearings would be the way to definitively show if you have an axle problem.

 

[Harold in CR]

From lots of mechanical experience, that side cover IS cracked and useless. Try to fit that same bearing into that side cover. I would bet it will slip right in.

A ball bearing should turn freely after a few hours of spinning. If it feels "stiff" it could be NOT turning, and has definitely been spinning inside the case socket.

When the bike is running on the ground, as long as that case is ground out at the bearing, the entire magnet ring will be rubbing on the stator, BUT, not all at the same time, the weight of bike and rider will cause the stator to rub on the ground side of the stator, from the WEIGHT. Same as a flat tire is only flat on the ground side. It does NOT have to be oval shaped for this to happen.

Get another side cover, get BOTH new Japanese or German bearings and clean up those magnets with alcohol or something that won't attack the epoxy, and I would bet you are good to go, IF those magnets have not come loose from the friction heat from rubbing. THAT is the million dollar question.