Agattu Drive Problem?

tillson · Aug 8, 2009

The only thing that I can think of is the chain slipping on the motor drive sprocket. But the fact that it only starts after a hundred yards or so would probably rule that out.

JamesC · Aug 8, 2009

I would tend to suspect the hub before the motor - associated with the highest gears.

Has the chain done all of the 3500 miles ? Probably worn by now if it has, but I am not sure if it could cause vibration. I would expect it to slip on the motor sprocket first.

Is the back wheel running true through the brakes ? Again, not sure that it would cause vibration.

Back to the gears as the most likely.

Sorry - not very useful

James

tillson · Aug 8, 2009

Aldby said:
Not related to the problem, but there is a small amount of play on the chainwheel which I would guess is normal

Yes that is normal.

Are the symptoms evident in all gears ratios or just top?

flecc · Aug 8, 2009

Yes, either gearhub or the motor unit's internal gears giving you a problem. Of the two I think it's the Nexus hub since you mention a ticking noise, and there's nothing in the motor unit that could readily account for that, while there's plenty in the hub gear that could.
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Fecn · Aug 9, 2009

Aldby said:
It is one that is difficult to explain but very noticeable when riding. It is not noticable when starting off on a ride, but after a few hundred yards and having changed up through the gears a juddering sensation is felt through the pedals as if the drive was slipping somehow, accompanied by a drop off in performance. It is still possible to keep a reasonable speed, but more effort is required.
There is also a clicking sound which I thought might be the chain tensioner or drive sprocket, but they seem to be OK.

That sounds very similar to the behaviour my Agattu was exhibiting up until I gave it a full service last week. The motor sprocket was quite badly worn, so I swapped it around to face the other way, but the real problem in my case was that the chain was rather stretched.

Rather conveniently, I have a habit of taking and lots of photos of everything I do, so here's a couple for reference...

This is how it should look... (back when my bike was only a few weeks old)

With a worn out chain... (my bike last week now that it's nearly a year old)

As you can see in the bottom picture, the chain doesn't really fit the chain ring properly anymore - This makes the weird clicking when you pedal along. I had already turned the motor sprocket around before I took that photo, but the stretched chain and worn sprocket also meant that quite often, the sprocket would fail to engage properly with the chain, and only the very tips of the teeth were making contact and transferring power - This also made a juddering sensation and a weird noise when it happened - Sounded like the chain was rubbing against the plastic chainguard.

Andy Grayland · Aug 9, 2009

Do you mind if I ask how many miles you have done with that chain Fecn?

Fecn · Aug 9, 2009

Andy Grayland said:
Do you mind if I ask how many miles you have done with that chain Fecn?

I'm not 100% sure as I only fitted a speedo back at the start of May, but I reckon it's around 1500 miles in total. I know that doesn't seem like much given how worn the chain is, but it's very very hilly around here, and I do a lot of riding off road, often loaded up with panniers and a child. My first set of brake pads only lasted about 250 miles.

Aldby - Your sprocket looks about as worn as my one was, so I reckon that yes, it would be enough to cause the problem. Flipping my sprocket over stopped the judder, but the clicking remained - Hence the new chain too.

flecc · Aug 9, 2009

I agree with Fecn, the condition and settings of motor sprockets, idler arm and chain are very critical on the new Panasonic unit, partly due to the motor sprocket's small size. These problems were very rare with the old unit and it's 14 tooth motor sprocket.

Also the idler arm in the photo is out of adjustment due to that chain wear, the recommended setting is shown here.
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tillson · Aug 9, 2009

I haven’t had any problems with the drive, but this thread has prompted me to check my chain tension. I dropped from a 23T standard rear sprocket to an 18 T after doing about 200 miles on the bike from new. I removed three links from the chain when I made this change.

I have just checked the tension using flecc’s guide on his website (60-65 mm from centre of the motor drive shaft to centre of the tension idler) and found that I have a distance of 90mm! The wheel is as far back in the slots as it will go, so I reckon that I need to remove a further 2 links from the chain to achieve the 60-65 mm. That will make a total of 5 links removed, 3 to accommodate the smaller rear sprocket and two to compensate for what I assume is stretching of the chain.

The motor drive sprocket looks quite good which is probably due to the fact that I use the lowest power setting most of the time, but I am wondering if I should fit a new chain. Is it likely to snap after this amount of stretching?

tillson · Aug 9, 2009

The drive looks correct John. Looking at your motor sprocket, it seems no worse than mine and I don’t have any hint of trouble.

When you say the drive feels like jumping cogs, do you mean that the pedals jump momentarily? If the pedals jump, it could indicate that the hub gear is the culprit. If the pedals turn without jumping but you feel a heavy vibrating sensation, I would say that it is motor related, either drive sprocket or internal.

iaing · Aug 9, 2009

Aldby said:
My 21 month old Agattu with over 3500 on the clock has developed a fault.

It is one that is difficult to explain but very noticeable when riding. It is not noticable when starting off on a ride, but after a few hundred yards and having changed up through the gears a juddering sensation is felt through the pedals as if the drive was slipping somehow, accompanied by a drop off in performance. It is still possible to keep a reasonable speed, but more effort is required.
There is also a clicking sound which I thought might be the chain tensioner or drive sprocket, but they seem to be OK.

I'm wondering if it is something internal, motor or Nexus hub, but I am not going to venture in there as the bike is still under warranty.

Any ideas or suggestions?

J hn

Hello

I know this is very basic, but you have checked the red lines on the Nexus hub are lined up correctly? I had the same sounding problem and to my relief that was all the problem was.

Iain

Agattu Drive Problem?

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