A single click at one crank position, always on the same pedal at the same point in the stroke, is almost always mechanical rather than motor electronics — and the good news is the top-of-stroke, load-onset timing narrows it right down.
The most likely culprits, cheapest to check first:
1. Pedal or cleat interface. The classic. A click that appears exactly as you load the right pedal often lives in the pedal itself, not the crank.
Swap the left and right pedals over. If the click moves to the other side, it's the pedal/bearing/cleat — not the BB. Two minutes, no tools beyond a pedal spanner, and it eliminates the single most common cause.
2. Crank bolt / spindle interface. Your Urrun runs the Shimano EP8-family motor (DU-EP800, 60Nm RS tune on the 2022–2024 alloy frame). The cranks pinch onto the spindle, and if the pinch bolts or the drive-side interface have worked slightly loose, you get a distinct tick under initial load. Pull the crank bolt, check torque, clean and re-grease the spindle splines, torque to Shimano spec (the pinch bolts are 12–14Nm, the centre cap is preload only). Dry splines are a very common one-position click.
3. Chainring bolts / chainring-to-spider. Load onset flexes the ring against the spider; a loose direct-mount ring lockring or dirty interface ticks once per revolution at the power stroke. Check the lockring is tight.
4. The sprag/one-way clutch inside the motor. As
@Mikerb explained here, eBike motors use a sprag/freehub-style bearing to feed motor output to the cranks, and the crankshaft also carries the torque sensor. A click as assist engages under load
can be the clutch — but this is the LAST thing to suspect, only after you've ruled out pedals, cranks and chainring, because it's the one that means the motor comes out.
Diagnosis order that actually splits the causes:
• Swap pedals — does the click follow the pedal? → pedal.
• Click stays put → pull drive-side crank, clean/grease/re-torque splines, check chainring lockring.
• Still there with everything torqued and greased → note whether it clicks in
walk mode (no crank torque). If it clicks purely under pedalling load but never in walk mode, log it and get it to your dealer before warranty gets awkward — internal clutch/sensor work is shop territory.
Does it happen in every assist mode, and is it there with the motor switched off entirely? That last one tells us instantly whether the motor's involved at all.
