Snap sound during hard cranking in taller gears?

[McRat]

This is a generic question for high torque center-mount eBike motors that use a derailleur, since it might occur across mfr's. Or it could be Yamaha specific. I don't know, it's my first center-mount eBike with a derailleur. I had a Bosch, but it had a CVT in the back. And the others are hubmotors which don't do this.

Specific test model - 2018 Haibike Trekking 6.0 Yamaha, 20sp Shimano:
I assembled this last night, then test rode it. I selected the small chainring (36T), and smallest cartridge wheel (11T) for the test.
When I set the bike to HIGH assist, and really mashed down on the crank - SNAP! A wicked noise occurs at about 10mph. The bike keeps pedaling, it was Just noise and impact vibration; I stopped and checked everything out. Fine. Two more tries with the same result.
What it feels like is when your motorcycle sprocket gets too worn and chain too loose, the chain actual 'jumps' a tooth. ie - The entire chain climbs the sprocket teeth until it can advance to the next tooth with a resounding CRACK sound.

Am I correct? Or is there something else this can be? In other words, do I need to have this looked at, or is this typical for a derailleur style center-mount 250w high-torque eBike when using a small, thin rear sprocket at max torque?

 

[JRA]

In the gear combination you describe the chain is at its most slack and due to this it might be jumping on the rear cog. Especially if the rear derailleur is at all out of adjustment due to cable tension.

 

[McRat]

Thanks. I should have considered the chain length slack with that gear selection. I will double check the cable tension. It did feel like it jumped teeth but I'd never seen it on derailleur before, just dirt bikes.

 

[JRA]

Keep in mind that proper cable tension only relates to the derailleur jockey wheel to cassette cog being well aligned. Note first how little tension in that gear combo that there is on the derailleur itself which affects chain tension overall and especially under torque could cause the chain to skip on the smaller cogs of the cassette.

 

[nublar]

Could be chain slap or chain skip. You are supposed to avoid the small/small and big/big combos to prolong drivetrain life. Small/small at high power will wear it out at an accelerated rate.

 

[bob armani]

I am also getting use to my new Yamaha motor on my Haibike Sduro 10.0. Recently noticed when I am in a higher PAS level before starting to move forward, while pressing down on the pedal, I feel some vibrations coming from the motor. I can feel it less in a lower PAS level, however, it seems like it is being produced by the current or by pulsations from the battery. There is no vibration when the system is set to Off.
Is this normal operation for the Yamaha mid drive motor? Anyone?

 

[Volt_Ampere]

Check your chain angle between the chain ring and the cartridge wheel when it's in that gear. I bet that the alignment is not good. You may have to change the shims on the chain ring.

 

[Marcomoto]

I am also getting use to my new Yamaha motor on my Haibike Sduro 10.0. Recently noticed when I am in a higher PAS level before starting to move forward, while pressing down on the pedal, I feel some vibrations coming from the motor. I can feel it less in a lower PAS level, however, it seems like it is being produced by the current or by pulsations from the battery. There is no vibration when the system is set to Off.
Is this normal operation for the Yamaha mid drive motor? Anyone?

I have a Yamaha PW-SE motor on a new Yamaha bike and it has the same sensation with the lightest of pressure on the pedal when stopped. Usually when ready and waiting at red light change. Lift foot to reduce press and it should disappear. I think it's completely normal as I have not had any motor issues whatsoever.

 

[bob armani]

I have a Yamaha PW-SE motor on a new Yamaha bike and it has the same sensation with the lightest of pressure on the pedal when stopped. Usually when ready and waiting at red light change. Lift foot to reduce press and it should disappear. I think it's completely normal as I have not had any motor issues whatsoever.

Marcomoto-
Thanks for the heads up! My first experience with the PW-X motor. I move an inch or two frontwards and backwards at a stop light while pressing the pedal and the pulsations are all new to me. I'll do the light foot press to reduce it. Ride safe!