How long should my chainwheel last?

[flecc]

I have been very conscious that successful products like the Giant Lafree became difficult to service as time went by. Possibly the market was too small.

I am hopeful that the 26v Panasonic bikes are out there in sufficient numbers to justify a new lease of life with fresh batteries etc.

James

The first series Panasonic unit was only ever fitted to the Lafree and BikeTec Flyers outside of Japan and despite the high regard for the Lafree only sold a total of 20,000 units worldwide. That, coupled with Giant's disillusionment at never making a penny profit on the whole Lafree series, made it highly likely that ongoing support would be minimal.

In contrast the new unit has been spectacularly successful and I daresay Kalkhoff alone soon passed the 20,000 sales mark worldwide, and numerous e-bike makes have been equipped with the new unit. Indeed the new unit has already lived in the market for more years than the original one and is still going strong. That popularity bodes well for an ongoing support market.

 

[tillson]

Tom
I have been trying to get my head round this question of the chainwheel simply being an "idler" with respect to the power provided by the motor.

The obvious difference compared with a traditional "idler" is that the chainwheel is between the driving sprocket and the driven sprocket, whereas an idler is more commonly found in the slack section of chain after the driven sprocket.

Furthermore, the chain makes a complete change of direction (and more) between entering the chainwheel and leaving the chainwheel.

So, you would expect the chain to pull very tightly into the "well" between the teeth when you are on maximum assist.

If, say, the chainwheel were on the thin side or the soft side, then the effort from the motor could still influence the "wear" or "deformation" in the valley between the teeth, and may give rise to a burr forming.

Now add in a bit of rider effort, and the chain may move a little out of the valley between the teeth towards the bottom of the leading edge, and some wear (and burring) would now show in the bottom leading corner.

If this were an unpowered bike, using rider effort only, then the maximum wear would be much higher up the leading edge of the tooth, giving rise to the "hook" shape that is often seen.


The power component from the motor might be why Danfoto talks about wear being on both faces of the tooth.

I think that the power assist may therefore affect the position of maximum wear on the chainwheel, and must add a component of pressure in the valley between the teeth that could accelerate the wear caused by the rider.

For discussion.

James

Your point about the chain wheel not being a traditional idler due to its placement on the tension side makes sense. I can also see how the chain tension induced by the motor will cause the chain to wrap more tightly around the chain wheel than if the bike were unassisted.

Looking at danphoto's pictures again it is difficult to see if the burrs are present at the bottom of the valley, between the teeth. There certainly seems to be burrs on the trailing edges of the teeth. I can understand how the wear pattern on the leading edge is created, and agree with your explanation regarding how the motor's influence will shift the wear created by the human input closer to the root of the tooth. But I'm still a bit puzzled by the wear on the trailing edge.

Regardless as to whether the rider and motor inputs are matched, I can't see why the trailing edge of the tooth should show signs of so much wear. As we have discussed, the chain wheel only exists in order to allow the rider to contribute to the overall power in the system, and that contribution is imparted by the leading edge.

Do you think that trailing edge wear is occurring because the chain is under tension as it exits the chain wheel and this prevents it from disengaging cleanly? This is a difference from an unassisted bike, where the chain is slack at point of disengagement and may fall away more cleanly. On our Panasonic bikes, there could be considerable tension and hence rigidity in the chain at this point.

(Note: I agree that danphoto's chain wheel probably wasn't hardened sufficiently / isn't up to the job. 1600 miles is not acceptable on a bike for which you pay a premium for supposed quality. I think 50 C should have sorted it out for him. But I am interested in the wear pattern.)

 

[flecc]

Do you think that trailing edge wear is occurring because the chain is under tension as it exits the chain wheel and this prevents it from disengaging cleanly? This is a difference from an unassisted bike,

Butting in at this point, a difference that affects this trailing edge wear is that the cranks and chainwheel are not mechanically locked together as on a normal bike. The chainwheel freewheel means that when a rider isn't pedalling or keeping pace with the motor output the chainwheel can be towed by the motor. As I remarked earlier, there will be some lag in motor response from torque signals which in turn means a degree of run-on when the chainwheel towing occurs.

 

[danfoto]

It's a shame because Kalkhoff had a reputation for dependable German engineering ...

Quite, and that was a major factor in our decision to buy two of them. However, one immediate consequence of this chainwheel lark is that when folks ask me what the bike is like, no longer will I be singing its praises like I have been for the last 18 months ...

 

[tillson]

Butting in at this point, a difference that affects this trailing edge wear is that the cranks and chainwheel are not mechanically locked together as on a normal bike. The chainwheel freewheel means that when a rider isn't pedalling or keeping pace with the motor output the chainwheel can be towed by the motor. As I remarked earlier, there will be some lag in motor response from torque signals which in turn means a degree of run-on when the chainwheel towing occurs.

I can see the point that you are making flecc, but the wear on the trailing edge of the chain wheel teeth must be minimal / non-existent due to the towing effect. The motor only has to overcome the friction in the chain wheel freewheel, which must be virtually nothing and certainly not enough to cause a burr.

 

[flecc]

I agree, and it emphasises that the softness of the chainwheel must be a major element for that wear pattern to result from such small factors.

With a well hardened chainwheel I don't think we would even be having this discussion.
.

 

[Deleted member 4366]

Dan, I've been looking at that chain-wheel again, and the damage to it doesn't look like wear. Was there an event that caused the chain to jam, or is it the result of the massive force you get when the chain rides up over the drive sprocket? Normally the chain would wear off those burrs, so it implies that they were caused by something other than normal wear. Have you experiences the clunking from the chain riding up the drive sprocket?

 

[Blew it]

Pressure versus impact

Curious as to why the trailing edge of the chainwheel teeth were showing burring, I had a quick look at the chainwheel of my own Panasonic unit. This machine has covered a similar mileage to the thread subject. As expected, the teeth leading edges are showing very slight wear, but no burring (plastic deformation). The trailing edges most certainly are showing burring, although not as pronounced as the O/P's.

Wear on the leading edges tends to be the result of rapidly increasing pressure on the teeth as the pedal stroke reaches maximum at around the horizontal, gradualy wearing the metal away...but no plastic deformation.

The plastic deformation of the trailing edges is indicative of impact, but I can't figure out how the chain rollers are striking the trailing edges to bring this about.

 

[danfoto]

Dan, I've been looking at that chain-wheel again, and the damage to it doesn't look like wear. Was there an event that caused the chain to jam, or is it the result of the massive force you get when the chain rides up over the drive sprocket? Normally the chain would wear off those burrs, so it implies that they were caused by something other than normal wear. Have you experiences the clunking from the chain riding up the drive sprocket?

I have no recollection at all of any sign of the chain riding up the drive sprocket. I'm actually an ex-toolmaker and biker, so I tend to be pretty much attuned to odd noises and such from machinery of any kind.

If it's impact damage, how come it's evenly distributed between all 41 teeth?

And ref the chain wearing off the burrs, I haven't measured anything (yet), but it looks like there's too much clearance for it to do that.

Once the new chains get here from 50 Cycles, I should be able to get straight on the case and do some proper comparing old with new. If I remember, I'll also do a rough-and ready comparison of the hardness of original and replacement chainwheels, but that will only be using the traditional hammer and centre punch method, maybe backed up with The File Test

 

[danfoto]

The plastic deformation of the trailing edges is indicative of impact, but I can't figure out how the chain rollers are striking the trailing edges to bring this about.

I note what you say, Blew it, but hang on until I can take some better snaps before you put your money on the trailing edge deformation being impact damage. Right now, it looks like nothing more than pressure pure and simple to me ...

 

[flecc]

I note what you say, Blew it, but hang on until I can take some better snaps before you put your money on the trailing edge deformation being impact damage. Right now, it looks like nothing more than pressure pure and simple to me ...

Yes, and it points back to what I've been saying here and previously. The only pressure that acts on the trailing edge is that of motor drive, run-on, or at times excess over rider effort such as occurs after a pedal thrust to set off when the motor drive power is at maximum just as the pedal arc reaches minimum input towards bdc.

Variations between units might just apply. The chainwheel is mounted on a pawl and ratchet housing sleeve over the pedal shaft and on a needle roller race. It's just possible that there could be a drag variation there due to tightness, roller damage or roller-cage damage. The needle roller assembly on the pedalshaft is shown by the left pointing number 4 arrow in this photo.

 

[danfoto]

flecc, just a thought but I'm not where the bikes are just now so I can't take a squint. How are the cranks held on? Or to be more precise, how do they come off?

 

[flecc]

If you have a look at this webpage on my Panasonic website and view the first few photos, you'll see how the cranks and chainwheel are mounted. This is the old unit, but this whole crank/chainwheel/torque sensor area is exactly the same on the new one.

 

[JamesC]

Regarding the burring that Danfoto has on the chainwheel, there has been several comments that the chainwheel might be "soft" / incorrectly hardened.

I had gained the impression that bicycle chainwheels are not always of hardened steel, some even being made of alloy.

I feel that the burring is much exaggerated on Danfoto's chainwheel because of the huge clearance down the side flanks of the teeth.

The regular clearance between the sideplates of the chain and side face of the tooth would be about 0.1mm (4 thou in English) on each side. Normal wandering of the chain would actually mean that it is often 0 on one side and 0.2mm on the other.

The limited clearance would maintain the sides of the tooth free of burrs on a "soft" chainwheel.

Danfoto is running 1/8" chain (3.18mm) on a chainwheel with 2.0 mm teeth.

Say, 0.6 mm (24 thou) each side, if by a miracle the chain runs centrally. This would be sufficient to leave a burr on both sides, although it is quite likely that there is a bigger burr on one side than the other.

Remember that the majority of Panasonic chainwheel users will either be using 1/8" chain on 3mm teeth or 11/128" chain on 2mm teeth with limited clearance for burrs to ever form.


Regarding the wear on the backside of the chainwheel teeth, I am wondering about the combination of the 41 T chainwheel and the large, 12 T, motor sprocket.

I have no experience of using the bigger motor sprocket with the biggest chainwheel, but I can imagine that the chain path is a little bit tight where the chain unwraps from the chainwheel.

I wonder whether there comes a point as the size of the motor sprocket increases, at which the chain rubs down the back of the chainwheel tooth. Does that sound possible ?

James

 

[flecc]

That mismatch cause of the excess chainwidth with a soft material chainwheel is entirely plausible James, but it still depends on traction from the motor sprocket to be on the trailing edge of course.

I don't think a larger motor sprocket would cause that trailing edge effect though. If you look at the photo below you'll see that even with a large motor sprocket, the chain run-off would still have the same relationship with the departure slope angle of the trailing edge chainwheel tooth. Also the fact of tooth engagement around the chainwheel wouldn't selectively allow excess pressure affecting the exit teeth on a chain in reasonable condition:

.

 

[RobF]

There were burrs on the chainring of a standard Brompton which was being worked on in my local bike shop recently.

The chain was sticking - not coming off the chainring cleanly - which was causing the rear sprocket to jump occasionally.

Investigation showed the cause to be a new chain fitted by the owner was the wrong width.

Fair play to Peter who owns the shop, he cleaned the burrs with a file rather than fit a new one and only charged the owner £20 for the correct chain and fitting.

That included quite a bit of labour because it took a while and a few test rides to bottom out the problem.

I, very generously, didn't charge anything for exercising my licence to interfere.

 

[danfoto]

Cheers flecc. Is that a standard crank extractor or do I need a special one?

 

[tillson]

Cheers flecc. Is that a standard crank extractor or do I need a special one?

When I removed the one on my bike, I used a standard extractor tool.

 

[flecc]

Cheers flecc. Is that a standard crank extractor or do I need a special one?

As Tillson says, yes it is for the Panasonic units.

 

[danfoto]

Cheers gents