The Kalkhoff Klunk - kontinued

[danfoto]

OK, I finally got chance to investigate further following the advice given to me on this thread

As far as I can tell, there's nothing loose anywhere. What there is, though, is a surprising amount of wear on the chainwheel. Bear in mind that these snaps are taken with the bike upside down ...

http://i79.photobucket.com/albums/j158/danfoto_photos/IMG_7714_zps6bbadeb8.jpg

http://i79.photobucket.com/albums/j158/danfoto_photos/IMG_7695_zps9408d85a.jpg

http://i79.photobucket.com/albums/j158/danfoto_photos/IMG_7694_zps5ce10323.jpg

That burr on the trailing side of each tooth is quite pronounced (maybe 25 thou or more), and just turning the cranks by hand against some resistance from the back brake produces a definite "snatching" and tendency for the chain to hang up, which might well translate into the "knocking" I'm getting when pedalling with power on.

I'm not entirely sure that I've found the cause, but obviously I need to do something about this! The first question is, though, is that amount of wear considered normal after 18 months and just 1600 miles?

Whatever, it's time for a new chainwheel, the fitting of which looks to be a straightforward job (?) and obviously a new chain to go with it, but what do you guys reckon to the wear on the motor sprocket? Leave it, turn it round, or replace it?

http://i79.photobucket.com/albums/j158/danfoto_photos/IMG_7708_zpsde6ae482.jpg

ETA - just to clarify my original post in that other thread, the muffled knock/clunk/whatever is definitely getting worse and more frequent, but it's only heard - nothing's felt and nothing "gives" when it does it, like it would if the chain was jumping a sprocket ...

 

[flecc]

That motor sprocket looks fine, but the chainwheel is bad. Frankly I think it probably wasn't hardened enough in the first place, since it shouldn't wear faster than the motor sprocket, if anything it should wear slower. It's very easy to change, just a circlip to remove to slot a new one onto the splines.

As for the clunk, are you sure the three motor mounting bolts are tight enough and the cranks really tight on the pedal shaft tapers? They are the most likely suspects.

 

[jackhandy]

Just out of interest, how much chain stretch is there?

If you put a tape-measure against the chain, keeping it pulled tight, a new chain will have one link bang on 12":

Whatever your chain measures over 12" is the amount of stretch.

Does that make sense?

 

[danfoto]

... the chainwheel is bad. Frankly I think it probably wasn't hardened enough in the first place, since it shouldn't wear faster than the motor sprocket, if anything it should wear slower.

That's exactly what I was thinking. I've certainly never seen one like it before!

I'll double-check the cranks again ASAP and come back. What's really bizarre is that the bike's totally clunkless with the power switched off, irrespective of how I pedal, but with power on the noise is there from time to time irrespective of which gear I'm in or of how hard I pedal ...

This is even worse than trying to get rid of the creak in a Brooks saddle used to be!

 

[mike killay]

Also check the chain for a tight link

 

[flecc]

What's really bizarre is that the bike's totally clunkless with the power switched off, irrespective of how I pedal, but with power on the noise is there from time to time irrespective of which gear I'm in or of how hard I pedal ...

Well that rules out the two things I mentioned. It also makes a transmission fault seem unlikely since that should show up when pedalling very hard. The mechanicals of the internals of the motor unit are very simple, leaving little that could cause a clunk. A broken nylon gear tooth wouldn't be intermittent, leaving only a unit bearing breaking up as a highly unlikely and very faint possibility.

Probably best to just replace the chainwheel and chain for now to see the outcome.

 

[robinnj]

Motor sprocket

That motor sprocket looks fine, but the chainwheel is bad. Frankly I think it probably wasn't hardened enough in the first place, since it shouldn't wear faster than the motor sprocket, if anything it should wear slower. It's very easy to change, just a circlip to remove to slot a new one onto the splines.

As for the clunk, are you sure the three motor mounting bolts are tight enough and the cranks really tight on the pedal shaft tapers? They are the most likely suspects.

Hi, I have had my Kalkoff for 2 years and done about 2500 miles. I have changed the motor sprocket twice in that period, the second time at about 2000 miles. I had a similar problem to what you are describing and changing the motor sprocket fixes it each time. You can hardly see any wear, but if you compare a new one and an old one you can just make out a difference.
Hope that helps.

 

[danfoto]

Cheers chaps. The chain's actually getting a bit worn now, but definitely hasn't any tight links. I'll email 50Cycles and see how they feel about a new chainwheel under guarantee.

Right now, the best hope seems to be new chainwheel and chain, and while I'm at it, I might as well reverse the drive sprocket - especially in view of what robinnj says ...