How long should my chainwheel last?

[JamesC]

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.

Flecc, is there a simple possibility that the freewheel in the Nexus hub is stiff or seized, and that all of the freewheel has been happening at the Panasonic chainwheel ?

Would that be a sufficient pressure on the back of the chainwheel teeth to cause some wear ? Probably not.


With the chainguard removed, it is easy to see that the chain keeps moving for about one revolution when you stop pedalling, caused by the short spell of motor overrun.

Normally this is the only occasion that the freewheel at the motor end gets used.

When the motor overrun stops, the freewheel in the hub takes over and the chain stops moving.

Have you ever known the freewheel in the hub to stiffen up, to the point where all freewheeling moves to the motor ? I guess that this would at least mean that the back of the chainwheel teeth are being used, albeit gently.

James

 

[flecc]

I've never known that on any Nexus hub gear James, and even if so, the chainwheel pawl and ratchet freewheel is unlikely to apply any appreciable drag. However, as I observed above, binding of any kind in the needle roller assembly supporting the chainwheel mount will impede the chainwheel freewheeling action. It's easy to check if the freewheeling action of the chainwheel and/or hub gear is binding though, just by spinning the cranks backwards when stationary.

 

[danfoto]

Gosh, this is all good stuff! Just by way of a lack-of-progress report from here, I've finally found my crank extractor so all I'm waiting for now is the chains to come from 50 Cycles ...

 

[danfoto]

And I'm still waiting for the chains from 50 Cycles. An enquiry via their chat thingy on Friday got me nowhere and I'm still waiting for a reply to the email they got first thing this morning, so I just now gave in and phoned to ask when I might expect to see the chains I ordered and paid for last Wednesday.

"They came into us this morning" says Matt.

"Ah. So you were out of stock when I ordered them and nobody told me."

"Well I wasn't here last week" says Matt.

Apparently I might get them on Wednesday.

I do hope so, because the wear's now bad enough for the chain to come off the chainwheel ...

 

[JamesC]

And I'm still waiting for the chains from 50 Cycles.

Apparently I might get them on Wednesday.

I do hope so, because the wear's now bad enough for the chain to come off the chainwheel ...

Sorry that you have not yet been able to have a go at your wear problem.

Before dismantling, I still think that it would be worth a short ride without the chainguard, to see if the chain continues to move when you stop pedalling.

If you really have wear on the trailing side of the teeth on the chainwheel, it seems likely that the chain is being pushed onto the chainwheel by the rear hub when you stop pedalling, and meeting some resistance in spinning the static motor.

This may be a complete red herring, but I have experienced this (with a different type of rear hub) when the chain was contacting the casing of the hub, which of course is still spinning with the rear wheel when you stop pedalling.

With the Nexus hub, this effect may be possible with a small hub sprocket (say 16 teeth), if it has been incorrectly fitted with the dish facing inwards towards the hub, leaving very little clearance between hub case and chain.

James

 

[danfoto]

Oh I'll certainly check that, James, but a pound to a penny says it's not the freewheel.

And before anybody asks why I need to wait for the chains from 50 Cycles, it's so (a) I can upend the bike and do everything in one hit and (b) I've got all the replacement parts from them so there can't be any nonsense in the future about invalidating the guarantee.

 

[JamesC]

a pound to a penny says it's not the freewheel.

Completely agree, but that only applies when the chain sits neatly on the sprocket and cannot touch any of the other rotating parts.

 

[danfoto]

Well, it's all had to change today 'cos I'm going to be pushed for time tomorrow when the chains come (as I am assured that they should).

Long story short, I now know that ...

(a) There was no sign at all of anything amiss when coasting downhill with both power and chainguard off

(b) My Agattu had a 35T chainwheel with an 11T motor sprocket but now has a 41T chainwheel with a 12T motor sprocket

(c) On examining the original chainwheel more closely off the bike, I'm now sure I'll never understand this deformation. I have never, ever, seen a chain sprocket wear like this, whether on a bicycle, motorcycle or machine drive. There is no sign at all of a hooked tooth developing. The metal has just burred over, rather than worn away.

(d) Matt at 50 Cycles has managed to recover the situation somewhat with regard to my opinion of the firm.

Whatever, the chainwheel and chain are truly FUBAR and I've strained my brain enough now trying to fathom it all out. New chainwheel and motor sprocket are on, and idlers and back sprocket are now clean. All that remains is to fit the new chain and see how I get on with the new gear ratios ...