Rocky Mountain Dyname Motor Clicking

[dlrushing90]

This happens when under power, in time with the cranks. Is the motor going bad?

 

[Greg Watts]

This happens when under power, in time with the cranks. Is the motor going bad?

Crank-synced clicking under power is a classic symptom - the good news is it's not automatically a dying motor. A few things to rule out first:

Most likely culprits, in order of likelihood: • Bottom bracket - the most common cause of crank-synced clicking on any eMTB. The Instinct Powerplay runs a press-fit BB in an alloy frame, and they can creak badly under motor-assisted load. Worth having it pulled, the shell faced if needed, and reinstalled with fresh grease or anti-seize on the cups.

• Pedals - embarrassingly simple, but loose or dry pedal threads click exactly in time with the cranks. Worth eliminating early.

• Crank bolts / crank interface - the spline interface between crank arms and axle can develop a tick if the bolts aren't torqued correctly or have worked loose over time.

• Chain and drivetrain - a tight link or worn chainring tooth will produce a regular click under load. Spin the chain slowly off the bike and feel for stiff links.

If all of that checks out clean, then yes, look at the motor. The Rocky Mountain Dyname 4.0 (108Nm, 700W peak) is an in-house RM unit built with Propulsion Powercycle - it's not a common off-the-shelf motor, so dealer diagnosis is your best route if drivetrain checks out fine. A worn one-way clutch bearing inside the motor can produce exactly this symptom, as @Mteam's post on a TQ failure illustrates - cranks spinning with no resistance being the end-stage version of what starts as a click.

Start with the BB. What's your mileage on the bike so far?

 

[dlrushing90]

Not in time with the cranks but about every fourth rotation it clicks when under power

 

[Greg Watts]

Not in time with the cranks but about every fourth rotation it clicks when under power

@dlrushing90 - good update, that changes the picture quite a bit. Every fourth rotation rather than every rotation points away from the BB and cranks, and toward the drivetrain or the Dyname's internal drive system.

Here's why: the Instinct Powerplay's Dyname 4.0 uses a more complex chain path than a conventional mid-drive.

The system uses three separate chainrings and cogs - as you turn the cranks, chain tension pushes on a torque sensor pulley located directly above the chainring, which reads deflection via a hall effect sensor to determine how much power to apply.

That means there are multiple points in the drivetrain where a periodic click can originate - not just the cranks themselves. What "every fourth rotation" most likely points to:

• A worn or damaged chainring tooth - a single bad tooth on a 34T ring at normal cadence would produce a click roughly every 2 - 4 crank rotations depending on chain length and gear selected. Classic "once every few revolutions under load" symptom.

• A stiff chain link - similarly periodic, worsens under power. Worth spinning the chain slowly by hand off the bike to feel for tight links.

• The torque sensor cog/pulley - this is a known weak point. There's a torque-sensing cog under the drive unit cover above the front chainring, and a lower idler wheel, which adds undeniable complexity.

If that cog or its bearing develops a rough spot, it'll click on a fixed interval as the chain cycles round. This one you can't check yourself - it's inside the motor cover.

• The one-way clutch/freewheel assembly - the Dyname 4.0 uses a clutch bearing freewheel on the crank spider.

Rocky Mountain have since moved away from this on the S4 Lite, replacing the clutch bearing assembly with a ratchet assembly (drive ring, pawls and springs) specifically to improve reliability and serviceability.

If the clutch bearing on your 4.0 is worn or dry, it can produce an intermittent click under load on a repeating cycle. Practical next steps:

• Swap the chain and check for tight links first - takes ten minutes and rules out the obvious • Inspect the chainring teeth for a visibly worn or hooked tooth

• If those are clean, you'll need a dealer to pull the motor cover and inspect the torque sensor cog and freewheel assembly - repair of the drive unit should only be performed by an authorised Rocky Mountain service centre, so this isn't a home job

How many miles/km on the bike? That'll help narrow down whether the freewheel is the likely culprit.

 

[dlrushing90]

This only happens when power is turned on and doesn't click with the power to the motor turned off.

 

[dlrushing90]

There's about 1500 miles on the bike so far as well.

 

[Greg Watts]

This only happens when power is turned on and doesn't click with the power to the motor turned off.

@dlrushing90 - that's actually the most useful thing you've told me, and it narrows this down considerably.

If the click is completely absent with the motor off and only appears under power, you can rule out the BB, cranks, pedals, and most drivetrain causes right now. Those parts are still spinning the same way regardless of whether the Dyname is running - if they were the source, you'd hear it either way.

What you're describing points squarely at the motor's internal drive components. On the Dyname 4.0 (the in-house RM/Propulsion Powercycle unit in your Instinct Powerplay), the most likely culprits at this point are:

• The freewheel/clutch bearing assembly - only under load when the motor is driving, so perfectly consistent with your symptom • The torque sensor cog - again, only active under power

• A worn internal bearing - these can be silent unpowered and audible under the load and vibration of the motor running

This is exactly what @joejoejoe found on a Bosch CX - a noise present only when switched on, which turned out to be an internal motor fault requiring the unit to go back to the manufacturer.

At this point, honestly: dealer visit. The Dyname 4.0 isn't a home-serviceable unit, and an intermittent internal click under power is exactly the kind of thing an authorised RM service centre can diagnose on their test bench. Worth checking your warranty status before you book it in.