Mid Drive Kit Install Part-1, Removing Bottom Bracket Cartridge.

Well, it’s tax return time here in the USA, and for many ebike enthusiasts it is the one time of the year that they indulge themselves, and buy the kit they have been dreaming of for months. Some of those new kits will be a mid drive, and often…the hardest part of the mid drive kit install is removing the stock bottom bracket cartridge. These pictures should give you an idea of what you are up against, so you can decide if you want to tackle this part yourself, or pass it on to a bike shop.


Should I, or Shouldn’t I?

First of all, contact your Local Bike Shop (LBS) because they really need your support. You ‘could’ buy a cheap bike from one of the “big box stores”, but they provide no service at all. Many LBS’s will gladly remove your bottom bracket cartridge for a little as $20 (or only slightly more), which is close to what it will cost to buy the tools you’d need to do it yourself. We all need to show our LBS’s that ebikes are a good thing, and will bring them business.

However, you might be one of those new ebikers that are mechanically inclined, and have a few tools already. If you suspect you might install two or three mid drives (one test ride usually leads to several purchases among your family and friends!), then buying a few more tools and performing this task yourself can be very personally rewarding.


Tools Needed

Double-check what type of bottom bracket (BB) style you have, and also the width of the BB-shell. There will be several variations, but this article will cover the most common Shimano type. The most common shell width is 68mm (2.7-inches), but the bicycle shown here has a 100mm (3.9-inches) BB-shell width.

On some cartridge styles, the crank-arms are held onto the spindle-ends by a hex nut, or a common hex-head bolt (a 14mm socket would be a typical tool to remove the big box store bike crankarms). This bicycle is from the Electra company, and it’s crank-arms are held onto the spindle with hex-socket bolts (sometimes called “Allen” head bolts).




In the pic above, the tool shown on the far left is an 8mm hex bit, with a 3/8th-inch drive interface. On this Electra bicycle, both sides use a common “right handed” thread, so…both are “righty-tighty, lefty loosy”

The tool just to the right of it, is a common crank-arm removal tool. The dark outer part has threads on both the inside diameter and also the outside diameter. The silver part that is threaded into the center of the dark outer part could be described as a bolt. The outer part is threaded onto the crank-arms, and once it is fully seated, you hold it with one wrench, while you drive in the center bolt with a second wrench. This will pull the crank arm off of the “square-tapered” spindle ends.

The tool on the right is the Shimano-style bottom bracket cartridge removal tool. It has 20-splines, and on the far right is the retaining end-piece of the cartridge that it fits into. This tool is shown attached to a 1/2-inch drive “breaker bar”.


Let’s get to it

I recommend you start on the left side. It’s easier to see what’s going on, and once you are familiar with everything, you will have more confidence when moving on to the more difficult chain-side.

You don’t have to remove the pedals to do this, But I started there just to make the job a little easier. If you are removing your pedals first (which you really don’t have to for removing the BB cartridge, but you might be switching these pedals over to the new kit), my pedals take a THIN 15mm open-end wrench (I took an old wrench and “thinned” it on a grinder). The right-side pedal has normal and common right-handed threads. THE LEFT PEDAL HAS LEFT-HANDED THREADS, so…when removing the left-side pedal you move the wrench as though its a normal bolt and you are tightening it, to get it off.

Next (in the picture shown below) the 8mm hex bit is on a common 3/8ths inch ratchet. Hold the crank-arm still, and move the wrench counter-clockwise (lefty-loosy). This bolt has normal right-handed threads.




Once the stock retaining bolt is out, thread the outer part of the crank removal tool into the crank-arm recess. If it is inserted only a couple threads, it will likely strip-out the threads inside the crank-arm (especially if the crank-arms are aluminum), so make sure it is fully inserted. On this model of bike, I was able to insert the crank tool five full rotations.




Now, insert the center-bolt of the crank-tool. Hold the outer part with one wrench, while you turn the center-bolt with a second wrench.




Once the crank-arm has popped-off, it’s time to use the 20-spline cartridge removal tool, shown below on a 1/2-inch drive “breaker bar”. Part of the reason I want you to start on the left side is because…the left-side bottom bracket cartridge retainer is attached with common “right handed” threads. In the pic, you need to rotate the wrench counter-clockwise, “lefty loosey”. If it is on there very tightly, it can help to heat up the BB shell with a hair-dryer or heat-gun, in order to make the shell expand slightly.

On a new bike, this should unscrew without needing to add a long pipe to the 1/2-inch drive breaker bar (in order to add more leverage). However, an older bike will likely have some corrosion on it. This is especially true of steel frames with a steel-threaded cartridge. Here’s a video from “bikemanforu” that shows how rough this can be sometimes.




Now we move on to the chain side. The crank retaining bolt (in the pic below) is just like the other side, the common “lefty loosey” (move the wrench counter clockwise).




Just like before, once the stock retaining-bolt is out, move on to the the crank-removal tool.




In the pic above, back-off the center bolt of the crank removal tool, screw-in the outer part to the crank-arm threads as deep as possible. Hold the part that is next to the cranks, and turn the center-bolt with a second wrench. All operations shown in the pic above are “righty tighty” (clockwise).




DANGER! This is the part where you really have to pay attention. The right side of a common Shimano-style BB cartridge has LEFT-HANDED THREADS! This means to remove it as shown in the pic above, you have to turn the wrench CLOCKWISE. (You could call it “righty loosey”!). Again, the cartridge may be on there very tightly, and using heat to expand the shell slightly may help.

If its taking a lot of force to make any progress, you may find that the splined tool “pops out” before the bike part breaks loose. If this is happening to you, one method to deal with this is to make sure when you were shopping for a splined tool; you get the style that has a large hex around its circumference (like the one shown in the pic below) in addition to the standard 1/2-inch drive square hole on the end. This allows you to run a bolt and washer through the center, which will hold the splined tool tightly onto the cartridge end-cup.

On this particular model of bike (Electra Lux), the bolt thread is a rare 8mm X 1.00 (fine thread), and the proper bolt length to do this when using this model of splined tool is 30mm long with a single 5/16-inch washer (too long would be better than too short, because you could add more washers).




If you are using this method, you can now use a very long wrench to apply exceptional pressure to unthread the remaining part of the cartridge. I mentioned adding heat to expand the BB shell, if needed. You might also consider using some thread penetrant solution.

WD-40 is a common product to use for this. I have also seen “PB Blaster” work well on rusty threads. If you do a lot of work on disassembling rusty mechanical devices, I have also seen a DIY solution of 50%/50% mix of ATF (automatic transmission fluid) and acetone (nail polish remover). Spray it on, and let it soak for a while, and whatever fluid you used will “wick” into the rusty threads.




Although the cartridge fits pretty snugly, it should pull out by hand at this stage.




As soon as the threads have all been disengaged, be VERY careful not to “ding” the threads on the BB shell when sliding the cartridge out.




Examine the inside of the BB shell. Some bicycle models have the downtube intruding into this space just a tiny amount. If your bike is like this, you may need to remove the obstruction with a small Dremel power tool. Whatever you do, protect the BB shell threads. If they become damaged, you may need to take the frame to your LBS and have them “chase” the threads with a BB threading tool.




In the pic above, I am using an angle-grinder to remove the chain-guard support. Notice I packed the BB threads with tissue to keep shavings out. If you don’t protect them they might “look” clean afterwards, but once you begin installing the kit, a few tiny shavings on the threads can make your installation a misery.

I have scars on my hands, and I don’t believe in promoting the “nanny state”, but…I NEVER screw around with my eyes. WEAR EYE PROTECTION. It is the sign of a professional. Do it.




The kit shown is the Bafang BBSHD, which is factory-rated at 1000W, but can be controller de-rated to 750W, depending on the laws in your country. It can run on 48V or 52V, and if using the stock controller maximum setting of 30A, the 52V X 30A = 1560 watts of power.

This particular victim of my abuse is an Electra Cruiser Lux 7D. It is one of the few frames that will allow “some” mid drives to be mounted inside the frame triangle. Even if the drive could only fit to this frame by mounting it under the BB, it still would have worked fine. However, since it fits here OK (while still allowing a very large battery to be mounted in the central frame triangle), I am going to leave it mounted right here.

The Electra company also makes a frame called the Townie, and it is one of the most popular street commuter bicycles in the electric bike kit community. It uses an upright rider posture with a “feet forward” crank position. If using the Townie frame, the drive motor would be mounted just in front of the BB shell, rather than under it or inside the triangle.



I would like to mention again that you can save yourself a lot of time and trouble if you simply pay your local bike shop a small fee to remove the BB cartridge. That being said…thanks for reading, and ride safe!

Here is a short Luna Cycle video with more info on installing this kit:


Part-two can be found here, and it is about matching the connectors between the battery and controller. It covers the dry crimp method and also soldering.


Written By Ron/spinningmagnets, April 2016

Grew up in Los Angeles California, US Navy submarine mechanic from 1977-81/SanDiego. Hydraulic mechanic in the 1980's/Los Angeles. Heavy equipment operator in the 1990's/traveled to various locations. Dump truck driver in the 2000's/SW Utah. Currently a water plant operator since 2010/NW Kansas


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