Hello MikinBbikin,
An inch and a half of slop before engagement is not the i9 Hydra's fault — those hubs have 690 points of engagement, roughly 0.52° between clicks. You'd struggle to measure that with a micrometer, let alone feel an inch and a half of it. So the Hydras are off the hook. The play is somewhere else in the drivetrain.
Where the slack is actually coming from
In rough order of likelihood:
•
Loose crank arm on the spindle — by far the most common cause. If the drive-side or non-drive crank has even slightly backed off, you get a noticeable dead zone before the motor spindle starts driving the chainring.
@XFi found Cube Hybrid cranks could slip even at the spec'd 15Nm and needed retaining compound on the splines to stay put. Pull the crank bolt, check the splines for damage/wear, refit with the correct torque (usually 15–20Nm depending on motor — Bosch is 50–55Nm on the Gen 4/5 spindle bolt, FYI).
•
Worn chainring bolts or direct-mount interface — if it's a spider-mount ring, the bolts can loosen. If it's direct mount, check the lockring is properly torqued.
•
Motor internal play — some motors develop crankshaft slop over time.
@ceromx reported ~2mm of play in a Giant SyncDrive after 4,000km of wet riding. An inch and a half is way beyond that, but a sloppy motor combined with a loose crank can feel enormous.
•
Freehub pawls not engaging — possible but unlikely given the Hydra's design. If you spin the wheel by hand and the freehub sounds healthy and bites instantly, it's not this.
•
Cassette lockring loose — long shot, but worth a check.
Diagnostic order
1. Bike in a stand, gear engaged, hold rear wheel still, push down on a crank. Watch carefully — does the crank arm itself wobble on the spindle? That's a loose crank.
2. If the cranks are solid but the chainring rotates before the chain tensions, it's the chainring/spider interface.
3. If chainring and crank move as one but the cassette rotates before driving the wheel, it's the freehub (and you should ring i9, because that shouldn't happen).
4. If everything else is solid and the spindle itself has rotational play inside the motor, it's a motor warranty job.
What bike and motor are you on? That'll narrow this down significantly — torque specs and known weak points vary a lot between Bosch, Shimano, Brose and Bafang.
