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    Chain keeps popping off chainring

    I’ve got a Marin Larkspur 1 that I did a BBHSD mid drive conversion to. One of the things I liked about the Larkspur was the 11-51t 10 speed cassette that I came with. I’m currently running the stock Bafang chainring. The current problem is that my chain keeps popping off the chainring when I shift gears quickly, when I hit bumps in the road, and it’s particularly bad when I’m on higher gears. Some days I’ll need to stop 3 times on my way to work to get the stupid chain back on the chainring. I heard I might need a long cage derailleur to solve this problem. Does anyone have any recommendations on how to fix this? It’s a safety issue for me and put me in a predicament yesterday when the chain ring popped off in an area I couldn’t pull over. Thankfully it was downhill and I was able to coast to a pull over area.

    #2

    The Bafang chain ring is known to be crap. A Wide narrow type will hold the chain better. Luna sells some Eclipse models and Lekkie also (Luna may sell both).
    You should measure your chain line (1/2 seat post dia. + distance from post to center of chainring). Then see if your chain is running striaght in 5-6gear on 10s. There may be some adjustment needed to get there. Also any change in gearing up or down can be made then.
    The spec. on that says a Sunrace 10s 11-51 cassette, with Microshift Advent X deraillleur. This is already a clutch type MTB part and should be OK.
    Be sure the freewheel in the rear hub, and the one in the cranks at the motor are both spinning free. Light grease on those, not the heavy bearing and gear lube used elsewhere.
    So Chainline, freewheels, chainring. Most users toss the Bafang chainring pretty soon.
    I see you had some crank arm issues also. Those external parts on Bafang are not so good the rest of it is great.

    Comment


      #3
      The issue is not uncommon. It would help to know what front chain ring you used - the stock Bafang 46T steel "pie plate", or something else. Otherwise, is the bike's drivetrain still stock? You might try upping the derailleur chain tension.

      Retrorockit covered most of it, such as the chain line importance - often best corrected via the Luna Eclipse 42/48 or Lekkie 40T aftermarket chainrings (personally, I prefer the Lekkie, because of the pants cuff guard). In some particularly unruly cases, a chain guide is helpful (via a fixed-position front derailleur or a specialized device).

      Nice conversion choice, BTW - please consider documenting it for others over in the Builder Gallery​. There's not much on successful step-thru bike conversions (here's one I've done, and my sister rides this low step-over).
      Last edited by ncmired; 09-23-2023, 06:52 AM.

      Comment


      • Retrorockit
        Retrorockit commented
        Editing a comment
        I agree very nice bike to convert.

      #4
      A couple of other things come to mind for the O.P. Wide-range derailleur drivetrains have a fair amount of chain length and inertia that the derailleur has the tough job of corralling - especially in the higher gears, when there's more wrapped-up chain and less derailleur cage spring tension. Hence the adjustable tension, but it can do only so much. A too-long chain exacerbates the issues.

      Better chainrings are machined with wide-narrow teeth to hold onto the chain better, and both of the mentioned chainrings have this feature.

      Chain drops are reducible, if not completely resolvable.
      Last edited by ncmired; 09-24-2023, 06:25 AM.

      Comment


        #5
        Then there is this.
        ​ ​​ This chain guide came to be out of another DIY project here The Mid Drive Cassette Zip Tie Mod. This guide solved some problems peculiar to that mod. But also solved some more common ones too. AS you can see form the flat 50t chain ring and no Wide/ Narrow feature this bike has chain line issues. It might have been a

        For when you do something silly, like zip tie your cassette to the spokes so it actually pushes chain towards the chain ring. Or just refuse to do all the normal stuff.

        Comment


          #6
          ncmired I’ll be sure to upload some photographs soon! I just got the Lekkie 42t chainring and I got a bunch of other parts (cane creek thudbuster, new saddle, and Surly Moloko handlebars) that I’m going to install on my bike and my next ebike (Kona Dew) tomorrow.

          Comment


            #7
            Derailleur Hanger Alignment is out of wack! - Basically derailer is bent!

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