Back from the LBS. Very interesting. I set the bike up last night exactly how I always do after latest wheel slip. Had a long chat with the chief mechanic and explained the whole background, problem and circumstances. He agreed to give my setup a thorough checking out in terms of tightening torques, wheel alignment, gear setup and alignment and also brake setup. Also to check the frame geometry with their tool for that.
Verdict was :
- He could find nothing at all wrong with the way I set it up including torque used to tighten axle nuts (reassuring !)
- There is nothing wrong with the frame geometry - it is absolutely spot on
- The chain is in good order and the tightness of 1cm play is appropriate especially on a bike where the motor drives through the gears. In my experience, a further 1cm play results in speed drop of nearly 1.5mph in higher gears on the flat so this is essential for the proper performance of the bike to be maintained - notwithstanding what is stated in Kalkhoff's manual as to tolerances.
So he carried on and investigated everything which might feasibly be causing the slip not otherwise checked to date at my request. This is most likely a mechanical issue and not an eBike issue after all, unless the design cannot cope with being ridden under load (highly unlikely).
The frame is very strong and it is true - as you'd expect from Derby Cycles. This is not the issue. He did find the following :
- The drive side replacement (outer) washer sent by 50 Cycles and swapped over within last 50 miles was worn. This was replaced by a different washer by LBS without so much wear.
- The wheel was somewhat out of true. This was trued and a couple of spokes tightened up
- The bike was set up 'spot on', back to how it was when I delivered it
- There was a lot of material on the inner interface between hub and frame. Like so :
LBS felt the only thing they could think might be causing the problem was that this material was inhibiting the proper grip of steel on aluminium. But that is just a guess. So they cleaned out the hub (echoing RoadieRoger's suggestion) and reset everything.
They also suggested I might try using removeable threadlock next time the axle nuts are tightened up again like RoadieRoger said ! However mentioned that the axle nuts did not look as if they were damaged in any way so this ought not to be necessary.
All in all it is still rather perplexing but possibly illustrates how sensitive these systems are to the gripping parts being in perfect nick !
It is too early to tell whether this will resolve my problem but the next step is probably for me to take the bike for a long ride to see how it holds up. If it does hold up I will be relieved as bottom line is I don't really want to be sending bikes back and forth with pitlocks to be removed, boxing up, likely loss of use of my rack with click-fix rack bag, removal of accessories and pedals etc. etc. Plus I like my bike (and always have done) and only want to be able to use it for what I bought it for without it playing up like it has been. We shall see.
Nonetheless, I think brand new washers should be procured and installed as running on a less worn still used drive side washer is a temporary fix that possibly won't last as long as it ought to.