Bad chain skipping over gears

[creativepart]

I've only put 35 miles on my bike since installing a BBSDH mid-drive. At first, I didn't see any major issue but on my last ride (20 miles on a paved bike path) I started getting rapid chain skipping under load in the 1st and 2nd highest (smallest) gears. I've worked on re-indexing and setting the H-limit screw but nothing fixes it.

I don't see the skipping in the 3rd and 4th highest gear but the 2nd highest is REALLY bad-bang, bang, bang. I worked on the bike today, starting from scratch with setting up the indexing. Everything is fine in the bike rack. It's shifting completely. But as soon as it's under load in PAS 3 (out of 5) it will barely pedal without the banging of the skipping gear. I guess it's skipping over the top of the 2nd gear on the cassette but I can't really see it.

I stopped pedaling and just used the throttle and still it's bang bang bang as the chain is yanked over the gears.

The 9-sp cassette has less than 200 miles on it. The chain is only a month old. The first ten miles were trouble free.

I have the Lekki narrow/wide 46T chain ring and I used 2mm of spacers to clear the chainstay during the build.

Any help or suggestions would be appreciated.

 

[JES2020]

Mid drive's are notorious for wrecking chains. If you are new to mid drives all the more so, also if you are running a lot of power thru the chain or starting with a weaker chain, it could be so short lived.

 

[indianajo]

I've gotten used parts in new boxes from lawnmower shops & auto supplies. Where did you buy your chain? I'd measure the stretch with a gauge, about $13 . Stretch over 75%, new chain, new more honest supplier.

 

[Sierratim]

Certainly sounds like worn drive components, but the mileage wouldn't indicate this. Perhaps you got one or more counterfeit parts along the lines of what @indianajo suggests? Perhaps the quality level of the parts just isn't up to the torque the mid-drive motor can produce?

 

[Sierratim]

I have the Lekki narrow/wide 46T chain ring and I used 2mm of spacers to clear the chainstay during the build.

Any help or suggestions would be appreciated.

Another thought would be chain alignment. What chain ring setup did your bike have before installing the single ring Lekki? If it was a triple or maybe even a double it would have been setup to not use the inner most ring with the smallest cassette cogs. Even with a 2mm spacer to clear the chainstay there could be enough chain misalignment to cause your symptoms.

I suggest taking a look at the chain when it's in the middle most cogs of the cassette. It should be in a straight line to the chain ring. If not, more spacers are probably needed.

 

[JRA]

Might be stating the obvious here but how is your chain length? When in the small cogs there is the least amount of tension on the derailleur and a slack chain can cause skipping, maybe taking out a link or 2 will solve the issue, as long as there are still enough to accommodate the big ring that is.

 

[creativepart]

The chain is new, and I've adjusted the length to where I feel it's about as tight as I should go.

The bike started life in 2018 with a 9x2 drivetrain that used a double front ring and front derailleur. I bought it new but only rode it about 100 to 200 miles max and parked it. Then a year ago I pulled off the rear wheel and put a hub drive kit on the bike. The hub on the hub drive used a freewheel and not a cassette. I used a 8-speed freewheel with that rear hub drive setup. I rode it 1000 miles in that form. Then, a couple of weeks ago, I returned the driveline back to stock - I put the original wheel on the bike using the OEM 9-speed cassette (that had less than 200 miles on it) at that time I reinstalled the OEM 9-sp microshift click shifter for the rear derailleur but still left off the front derailleur. I rode the now-accoustic bike a couple of miles to insure it was all good. No chain skip.

Then I installed the mid-drive system. When I installed the mid-drive I changed the chain to a brand new 9-sp chain because I know mid-drives are hard on chains. So, now the bike has the OEM rear wheel, cassette, RD, and shifter but is driven by the new BBSHD mid-drive with a 46T Lekki chain ring.

As for chain line... when the chain is on the smallest (highest) gear it runs straight to the front chainring. When on the 4th (of 9) gears the chain is angled outward to the front chainring.

The only things I can think of that are still possibilities are:

1. Bent derailleur hanger
2. Bent derailleur jog wheel cage
3. Damaged 1st and 2nd gear cogs - even though there is low mileage - perhaps the skipping has damaged the gears quickly

So, I'm throwing parts at it now since I've tried everything adjustment-wise. A new hanger and a new Deore RD will arrive tomorrow. Also, I'm going to remove the Lekki and put the OEM Bafang chain ring on it and see if that does anything.

I appreciate the help. I wish I could ride and hold my camera down there to get a video of exactly what it's doing.

 

[JES2020]

The chain is new, and I've adjusted the length to where I feel it's about as tight as I should go.

The bike started life in 2018 with a 9x2 drivetrain that used a double front ring and front derailleur. I bought it new but only rode it about 100 to 200 miles max and parked it. Then a year ago I pulled off the rear wheel and put a hub drive kit on the bike. The hub on the hub drive used a freewheel and not a cassette. I used a 8-speed freewheel with that rear hub drive setup. I rode it 1000 miles in that form. Then, a couple of weeks ago, I returned the driveline back to stock - I put the original wheel on the bike using the OEM 9-speed cassette (that had less than 200 miles on it) at that time I reinstalled the OEM 9-sp microshift click shifter for the rear derailleur but still left off the front derailleur. I rode the now-accoustic bike a couple of miles to insure it was all good. No chain skip.

Then I installed the mid-drive system. When I installed the mid-drive I changed the chain to a brand new 9-sp chain because I know mid-drives are hard on chains. So, now the bike has the OEM rear wheel, cassette, RD, and shifter but is driven by the new BBSHD mid-drive with a 46T Lekki chain ring.

As for chain line... when the chain is on the smallest (highest) gear it runs straight to the front chainring. When on the 4th (of 9) gears the chain is angled outward to the front chainring.

The only things I can think of that are still possibilities are:

1. Bent derailleur hanger
2. Bent derailleur jog wheel cage
3. Damaged 1st and 2nd gear cogs - even though there is low mileage - perhaps the skipping has damaged the gears quickly

So, I'm throwing parts at it now since I've tried everything adjustment-wise. A new hanger and a new Deore RD will arrive tomorrow. Also, I'm going to remove the Lekki and put the OEM Bafang chain ring on it and see if that does anything.

I appreciate the help. I wish I could ride and hold my camera down there to get a video of exactly what it's doing.

Sound like you know what you are doing. I assume you have tested the chain for stretch and wear?
Is it a high power motor that could wear out the chain quickly?

What I am saying is, I would suspect the chain, even though it's new. It could be that it's already worn or it's not properly installed somehow, pretty easy to check and cheap to fix.

 

[creativepart]

Thanks. Yes, I have checked the chain - but again. It's new with literally 20-miles on it. I started with an extra 2-links in the chain but have removed those and don't feel it can go any shorter.

 

[JES2020]

Thanks. Yes, I have checked the chain - but again. It's new with literally 20-miles on it. I started with an extra 2-links in the chain but have removed those and don't feel it can go any shorter.

I see.
One thing you said, you don't "feel" you can go any shorter.
There should be a certain fixed limit to the chain legnth for your bike, and how to test it, do you "know" that your chain is within that limit?

 

[creativepart]

Yes, I do know how to test and size the chain. What I mean is, I don't feel I can go shorter without being too short as it is already shorter by 2-links than standard chain sizing. Plus, when in the biggest gear on the cassette the DR is stretched nearly horizontal.

At first I was concerned that the old chain was too short which is one reason that I quickly bought a new chain. I knew the old chain had over 1000 miles on it and so getting a new chain for the mid-drive was a forgone conclusion. But when I started getting some slipping, I immediately bought and installed a new chain to both start fresh, chain-wise and because I was concerned that the old chain was a bit short. The old chain was sized for the previous chainring which was a 44T and the new Lekki is 46T.

When the new chain made no difference I put the old shorter chain on and it too made no difference. In the end I ended up with the new chain... but shortened to the length of the old chain. Which as I said is about as short as I think I can go without ruining the chain.

The narrow/wide Lekki hangs on to chains more than a standard chainring. So, besides the parts I'm replacing tomorrow I'm going to change out the chainring to the OEM Bafang. It's a simple process. I have another 1mm BB spacer and I may try adding that as well. But first I'll see what happens when the new DR and Hanger come tomorrow.

 

[JES2020]

Yes, I do know how to test and size the chain. What I mean is, I don't feel I can go shorter without being too short as it is already shorter by 2-links than standard chain sizing. Plus, when in the biggest gear on the cassette the DR is stretched nearly horizontal.

At first I was concerned that the old chain was too short which is one reason that I quickly bought a new chain. I knew the old chain had over 1000 miles on it and so getting a new chain for the mid-drive was a forgone conclusion. But when I started getting some slipping, I immediately bought and installed a new chain to both start fresh, chain-wise and because I was concerned that the old chain was a bit short. The old chain was sized for the previous chainring which was a 44T and the new Lekki is 46T.

When the new chain made no difference I put the old shorter chain on and it too made no difference. In the end I ended up with the new chain... but shortened to the length of the old chain. Which as I said is about as short as I think I can go without ruining the chain.

The narrow/wide Lekki hangs on to chains more than a standard chainring. So, besides the parts I'm replacing tomorrow I'm going to change out the chainring to the OEM Bafang. It's a simple process. I have another 1mm BB spacer and I may try adding that as well. But first I'll see what happens when the new DR and Hanger come tomorrow.

Maybe it's different on your bike but when the DR is almost horizontal, then isn't the chain too short?

 

[creativepart]

Yes, that would mean that. Which is why I first tried a longer chain length. I exaggerated... It's not exactly horizontal, it's as horizontal as I would consider acceptable.

I just changed the chainring from the 46T Lekki to the OEM Steel Bafang 46T Chainring and took it for a ride. I only went 2.5 miles but it's marginally better. Now, it's only skipping in 2nd gear and it's not non-stop.

I don't consider this a fix, but it's a start. The Bafang chainring isn't as dished inward as the Lekki. So, perhaps this helped the chainline a little bit and this made it slightly better. It's too early to tell.

I'll certainly report back when I find the issue.

 

[theemartymac]

I wrecked a cassette in less than 500kms (300miles) with my Ultra Mid Drive. 8&9 (smallest cogs) went quickly as the majority of those miles were spent in those 2 gears, and once it started skipping, it failed very fast. Actually found micro-cracks in the gears after I pulled it. There were a few other minor alignment issues that may have contributed, but the big fix for me was to go larger on the front chainring to move the rear up to larger cogs for daily riding. It shifted my normal cruising gears up 2 cogs which engaged more teeth and distributed loads better. I also adjusted the chain line to optimize for 6/7 as that is where most of my riding is done now. I now have well over 1,000kms on the replacement chain and cassette, and it looks like I will probably get to 1,500kms anyway. Significant improvement.

And if you don't have a shift disconnect sensor, but extra-judicious with rolling off the throttle/PAS when shifting.

 

[JES2020]

"And if you don't have a shift disconnect sensor, but extra-judicious with rolling off the throttle/PAS when shifting"

Yeah that's why I really like the simplicity of the hubs, I'll give up a little of the simplicity for the geared hubs, for weight reduction and speed.

 

[PedalUma]

It is the B-screw.

Rear Derailleur Adjustment

The article will discuss adjustment of rear derailleur limit screws and indexing.

www.parktool.com

Not enough teeth are engaged. This will also exacerbate the problem, trashing the skipping components.

 

[theemartymac]

It is the B-screw.

Rear Derailleur Adjustment

The article will discuss adjustment of rear derailleur limit screws and indexing.

www.parktool.com

Not enough teeth are engaged. This will also exacerbate the problem, trashing the skipping components.

That was one of the adjustments on mine that seemed to help as well. The b-tension was way to slack when delivered. Tightening that up also made the shifts much crisper and quicker in general.

 

[PedalUma]

You bring it In by backing Out the B-screw. This skipping because not enough teeth are engaged in the highest (smallest) cogs. All the force will be then focused on three or four teeth. Not dispersed over five, six, or seven teeth. It happens on regular non-electric mountain bikes with strong ridders when they stand while in a high gear. The fix is easy but you will regrettably still need a fresh cassette and chain. It is the cost of tuition.
It was out of adjustment during the first 30 miles but because the parts were new it did not start skipping until they were prematurely thrashed.

 

[creativepart]

Still throwing parts at it - new DR Hanger and new Deore rear derailleur. I thought both of the oem items were slightly bent - and they were but it was very slight and the new items didn't fix the issue.

B Screw adjusted, it's not that.

New cassette and chain arrive Monday. A few of the teeth on the 2nd lowest gear do show some very rough teeth.

After these parts everything on the bike except the wheels, brakes and headset will be new.

I think it's going to turn out to be chainline.

On my hub drive bike I had a very similar problem. That wheel used a freewheel. So, I bought a new 9-sp freewheel for it. But the lowest gear skipped like this one does on the 2nd gear. So, I ordered a new 8-sp freewheel and 8-spd thumb shifter. Boom, that fixed the issue completely.

Of course, for this mid-drive I went back to my OEM wheel with it's 9-sp CASSETTE and I reinstalled the OEM 9-speed MicroShift shifter, too, of course. So, today when ordering the new cassette I ordered an 8-sp instead of a 9-sp and I still have the previous 8-sp Shimano thumb shifter. Accordingly, I ordered a new 8-sp chain to go with the soon to be new 8-speed drive train.

 

[PedalUma]

Okay. Now you are all set for the new cassette and chain. Then ride the bike like you would ride a horse you love and want to keep healthy. Or like you would drive a car that you want to keep and get good gas mileage out of. Avoid sudden lurches of power like jackrabbit starts. That will preserve the new drivetrain and provide better range per charge.