Agattu Chain Tensioner

[stokepa31_mk2]

I just came back from a long ride and noticed that the chain seemed very slack. One obvious thought was whether or not links were removed after my sprocket was changed to 18 teeth but on closer inspection the chain tensioner does not seem to be as free moving as it could be. if I turn the bike upside down and push the tensioner down, it does not spring back without encouragement.

anyone have any thoughts?

 

[HarryB]

Yes exactly the same as mine - see other post. http://www.pedelecs.co.uk/forum/electric-bicycles/2173-persistent-rattling-noise-chain-agattu.html

 

[flecc]

As I've remarked to Harry, these are strictly speaking not chain tensioners, and in fact the swing arm angle is designed to avoid altering the chain length directly.

As you can see from it's angle, the arm idler is there to wrap the chain tightly around the motor sprocket, and only tensions downwards at near 90 degrees to the angle needed for efficient fore and aft chain tensioning like a derailleur mechanism. It's the job of the dropouts to tension the chain by wheel adjustment.

I suspect a lot of the noises being made when the arm pivot is binding are due to the chain trying to jump the motor sprocket teeth, and this possible problem is unique to the new Panasonic unit. The old unit with it's much larger 14 tooth motor sprocket only suffered jumping when the motor sprocket was worn out, and a poorly maintained and binding arm pivot didn't seem to have any ill effect.
.

 

[stokepa31_mk2]

As I've remarked to Harry, these are strictly speaking not chain tensioners, and in fact the swing arm angle is designed to avoid altering the chain length directly.

As you can see from it's angle, the arm idler is there to wrap the chain tightly around the motor sprocket, and only tensions downwards at near 90 degrees to the angle needed for efficient fore and aft chain tensioning like a derailleur mechanism. It's the job of the dropouts to tension the chain by wheel adjustment.

I suspect a lot of the noises being made when the arm pivot is binding are due to the chain trying to jump the motor sprocket teeth, and this possible problem is unique to the new Panasonic unit. The old unit with it's much larger 14 tooth motor sprocket only suffered jumping when the motor sprocket was worn out, and a poorly maintained and binding arm pivot didn't seem to have any ill effect.
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Interesting Flecc and I can see from looking at the motor sprocket when the bike is upside down that the chain is indeed struggling to go easily round the motor sprocket without kinking and jumping. I will first attempt to shorten the chain. I guess its important to keep the chain well lubed too to stop kinks etc? Can I go to work on any link of the chain with my chain tool?

 

[flecc]

Yes, any link Paul. Be careful not to shorten too much so that there's insufficient wrap around that motor sprocket.

P.S. Make sure there's no tight links on the chain too, they should all pivot freely.
.

 

[HarryB]

While I agree that the primary function of the tensioner is to keep the chain around the motor sprocket (of course a normal single speed/hub gear doesn't have one), it certainly does tension the chain. I think there is some problem with lubrication at the assembly stage at the factory. Mine is now working very well indeed after a good oiling. On Thursday and Friday it was slipping and when the chain came off, the tensioner was stuck at its uppermost position, once yanked down the chain stayed on. However the motor always felt like it was taking up some slack and this feeling has now disappeared. I have also checked the chain length and I have judged it OK - if I simulate removing another link it is too tight so I have left it. I am sure it will be ok.

I would advise owners to check the up and down movement of this tension and if it feels tight and sticky give it a good oiling.

 

[stokepa31_mk2]

Ive just compared my wifes bike with mine in terms of the tensioner and hers is very free moving (its only done 5 miles). Going to give the chain a good acetone bath and relube both it and the tensioner. also need to check with the guys that did the sprocket for me to see if they took links out or not.

 

[stokepa31_mk2]

forgot to say - it would be good if Aldby, Musicbooks and Essexman et al could comment on their tensioner.

 

[HarryB]

Ive just compared my wifes bike with mine in terms of the tensioner and hers is very free moving (its only done 5 miles). Going to give the chain a good acetone bath and relube both it and the tensioner. also need to check with the guys that did the sprocket for me to see if they took links out or not.

You should be able to tell if your chain length is right by checking against your wife's agattu. On my bike the tensioner is almost fully extended and if you remove another link then the tensioner would sit quite high up. Flecc has advised not to have the chain too tight so I believe mine is about right. I suspect yours will be too and advise lubricating the tensioner so it becomes free moving as your wife's is. This should solve the problem.

I believe a lot of the unhappiness I have felt about the hub is in fact because the tensioner has not been doing a good job. The jumping and slipping has been a problem with the chain not the hub so I am looking forward to my ride to work on Monday.

 

[stokepa31_mk2]

You should be able to tell if your chain length is right by checking against your wife's agattu. On my bike the tensioner is almost fully extended and if you remove another link then the tensioner would sit quite high up. Flecc has advised not to have the chain too tight so I believe mine is about right. I suspect yours will be too and advise lubricating the tensioner so it becomes free moving as your wife's is. This should solve the problem.

I believe a lot of the unhappiness I have felt about the hub is in fact because the tensioner has not been doing a good job. The jumping and slipping has been a problem with the chain not the hub so I am looking forward to my ride to work on Monday.

Cheers Harry / Flecc

Ill be sure to do the tensioner first and take it from there. Good luck on Monday

 

[the_killjoy]

With the jumping on the front sprocket does it mean that from the mechanical point of view that instead of dropping the rear sprocket from 22 to 18 it would be better to regear by raising the front from 12 to 14 ?

 

[flecc]

With the jumping on the front sprocket does it mean that from the mechanical point of view that instead of dropping the rear sprocket from 22 to 18 it would be better to regear by raising the front from 12 to 14 ?

The standard front motor sprocket is 9 tooth, No 12 is listed and it's doubtful a 14 tooth would fit into the available space. The listed sprockets are 8, 9 and 11 tooth, intended for different road wheel sizes, and to my knowledge only available in the West from BikeTech of Switzerland via their dealers.

The 11 tooth would help slightly but would change the cadence due to the Panasonic unit's design. It's unnecessary if the idler arm pivot is free running, as it will be with more use. I think this problem has only cropped up through the newness of the bikes and the pivot being tight and dry.
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[HarryB]

...I think this problem has only cropped up through the newness of the bikes and the pivot being tight and dry.
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I am sure it is down to the lack of lubrication. The pivot was completely dry and I think it should have been assembled with grease. There seems to be a good dolup of grease on every pivot on the bike except this one. We will see how the journey is tomorrow but I am very confident. I think instead of oil I think I will undo the screw and use some grease rather than oil as that should be a longer term solution.

 

[flecc]

I am sure it is down to the lack of lubrication. The pivot was completely dry and I think it should have been assembled with grease. There seems to be a good dolup of grease on every pivot on the bike except this one. We will see how the journey is tomorrow but I am very confident. I think instead of oil I think I will undo the screw and use some grease rather than oil as that should be a longer term solution.

I agree completely Hal. The old units were also shipped with dry arm pivots, probably because this was an external part, but as said, it didn't matter with their larger sprocket. Once there's a touch of wear it won't matter though, and this could be Panasonic's intention, since wearing out could never be an issue with such a low rate of rotational movement. The downside of course is that lubrication will markedly slow that wearing, possibly preventing it freeing up appreciably. Pity there wasn't a bit more clearance in the first place, but no doubt they'll learn and modify.
.

 

[musicbooks]

I suspect a lot of the noises being made when the arm pivot is binding are due to the chain trying to jump the motor sprocket teeth, and this possible problem is unique to the new Panasonic unit. The old unit with it's much larger 14 tooth motor sprocket only suffered jumping when the motor sprocket was worn out, and a poorly maintained and binding arm pivot didn't seem to have any ill effect.
.

Is this something to worry about? I find that the rattling noise (like a twig in the spokes.. regular but random) increases with the steepness of the hill. Is it possible to provide a photos of correct positions?

bw
musicbooks

 

[flecc]

It's not something to worry about, since as I've observed, as wear occurs it's self curing, and many bikes will probably never be affected anyway. The arm position isn't critical, but this is normal on a correctly working bike, upside down in this photo:

 

[musicbooks]

It's not something to worry about, since as I've observed, as wear occurs it's self curing, and many bikes will probably never be affected anyway. The arm position isn't critical, but this is normal on a correctly working bike, upside down in this photo:

Thank you Flecc,
Glad you said 'upside down'! I'm glad too its nothing to worry about, just rather irritating when cycling. So tightening the chain may not have the desired effect of silencing the twig?

bw
musicbooks

 

[flecc]

No. As you can see from the photo, if the chain is too tight, it might sometimes wrap around the motor sprocket even less, and therefore be even more likely to try to jump over the teeth.

However it's impossible for me to say what your ticking noise is without being with the bike, but as a generalisation, these ticking sounds don't cause problems.

They can come from freewheel pawls in the hub or motor, from tight chain links, from misalignment of front and rear sprockets, from wheel out of line causing sprocket tooth catching, from a bent sprocket tooth catching likewise, or something lightly touching somewhere for example.
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[musicbooks]

No. As you can see from the photo, if the chain is too tight, it might sometimes wrap around the motor sprocket even less, and therefore be even more likely to try to jump over the teeth.

However it's impossible for me to say what your ticking noise is without being with the bike, but as a generalisation, these ticking sounds don't cause problems.

They can come from freewheel pawls in the hub or motor, from tight chain links, from misalignment of front and rear sprockets, from wheel out of line causing sprocket tooth catching, from a bent sprocket tooth catching likewise, or something lightly touching somewhere for example.
.

When I adjusted the gearing (with the bike upside down) I noticed that the rear brake pad rubs on the wheel rim at a single point as it rotates. It is difficult to tell and the eye does play tricks when trying to judge but the rear wheel could be slightly buckled. I can't be 100% sure about that though. Is there any way to test it?

If it was buckled (perhaps a knock in transit) would this contribute to the crackling sounds?

Having said all that, would you recommend that I take it to a bike shop and let them tinker, or is it not worth it?

bw
musicbooks

 

[flecc]

It's unlikely to be buckled given th build standard on these wheels, but worth a check. It's common to have a very small sideways deviation, and if a brake pad is sitting close it can touch with only a minute variation in the rim.

A good local bike shop will be able to identify the ticking sound if it's from the bike or gear hub, and will only be unable to do so if it's from within the motor unit. They'll also be able to say if the wheel needs attention, so you might consider it worth getting an opinion on those.
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