Mongoose – Chapter 5 (Motor Install)

There are about a billion step by step Youtube videos and forum posts describing the steps that go into installing a BBSHD onto an existing donor bicycle.  They already do a great job so I won’t try to get too deep into the weeds on that.  I will say that installation on the Envoy was simpler than my previous builds on different bikes, which is only a good thing for you if you aren’t familiar with installing a BBSHD onto a bike.

Step 1: Prepare the bicycle

You are going to be pulling apart some things and replacing them, so you’ve got some prep work to do.  Myself personally, I decided to do the following which you should consider optional.

9 Speed Conversion

I converted the bike to a 9-speed from its factory 8-speed.  You already have to say goodbye to the stock shifters Mongoose gives you with the bike since they are integral with the brake levers, which themselves have to go.  So I decided to bump up my options a tad.  8, 9 and 10-speed systems will fit interchangeably on the same hub.  I also have other bikes that are 9-speed and I like to have common parts between them.  Plus, I already had a cluster in my parts pile that was 9-speed :-).  So 9-speed it is.

As noted in the Motor Choice chapter, if you decide to stay 8-speed, you still need to replace your cluster as part of your mid drive upgrade.  A Shimano CS-HG31 8-speed cassette in 11-34T is about US$17.50.  You can bump that up to an HG-50 with nickel-plated steel cogs (not a bad idea) for about US$22.  At that point you will need to buy yourself some 8-speed shifters since, as noted above, the stockers can’t stay.  You’ll be able to keep the derailleur that comes with the bike (which frankly is not something that appealed to me… the one on my bike worked poorly and was clearly a basic, commodity component).

So here was my prep given this 9-speed conversion:

  1. Remove the handlebar grips without destroying them.  I used a jeweler’s screwdriver to lift up the edge of the grip, which let me get a WD40 straw nozzle in there and give it a spritz.  A couple of those and I was able to work the grip loose without having to cut it off.
  2. Release the brake cables.  This entails releasing the cable from the brake caliper so the lever flops free.  Then you can easily remove the cable from the lever.
  3. Release the shifter cables.  Release the cable from the derailleur and then pull the cable out of the housing so it is free.
  4. Remove the shifter/brake lever from the handlebars.  Just loosen the screw and slide them off.
  5. Remove the chain.  The Mongoose chain does not have a master link, so you will need to use a chainbreaker.  This chain will not be re-used.
  6. Remove the front derailleur from the bicycle.  Not used on a mid drive, so it goes into the bin.
  7. Remove the front derailleur cable housing.  Since the cable is routed thru the frame, this will give you an unused entry and exit hole in your frame which you’ll want to seal up with something.  I used a bit of rolled up mastic tape.
  8. Remove the rear wheel and replace the rear cluster.  You’ll need a chain whip and a cassette removal tool for this.
  9. Remove and replace the rear derailleur (optional.  See above.)
  10. Remove both pedals from the crankarms (or better yet don’t install them in the first place when you take the bike out of the box).
  11. Remove the crankarms.  You will need a proper sized socket to get the bolt out, then a crank puller tool plus a big wrench to finish the job.  Repeat for the other side.
  12. Remove the bottom bracket.  You’ll need a standard bottom bracket tool such as a Park BBT-32, and again a big wrench to turn it.

Prep work complete.  The bike now looks like the picture below, minus the big cargo net.  You’re ready to install the motor now.

IMG_20190928_102436
Fig. 2:  At this point your bike will look about like this:  No pedals, nothing on the bars and loose wires hanging around.

Step 2: Attach The Motor

It will fit right into the empty hole that used to house your bottom bracket.  At this point the motor is hanging straight down in the bottom bracket thanks to gravity.  You will want to dig into your installation kit’s parts bag and retrieve the two M6 bolts and the fixing plate that will clamp your motor to the bottom bracket.

One side of the fixing plate is ridged. These ridges are there to bite into the bottom bracket.  they go a long way (most of the way) towards holding the motor up and in place.  Before you slide that plate onto the motor’s axle, you need some spacers between it and the motor to support the plate, but not so many that you get in the way of the plate clamping to the bottom bracket.  Usually I use fixed-size steel spacers that I get from McMaster-Carr (you can buy them in various lengths in 1mm increments), but in this case I just used three M6 washers and got a perfect fit.

IMG_20191008_174717
Fig. 2a: The fixing plate, with those all-important ridges that must directly contact your bottom bracket.  In background: a couple of outer trim rings, and the  M6 bolts you’ll use to attach that plate to the motor.

Using just this plate clamped gently to the bottom bracket, its possible to get a provisional fit on the motor without fully tightening it.  Here’s where, essentially, the only hiccup in the installation occurs:  The rear shifter cable exits the frame just ahead of the bottom bracket, and travels under it.  If you rotate the motor up as high as it can go – which is the most desirable position – it will pinch the cable and seize it up.  So you have to back off a bit.  The picture below shows what my cable looks like after a successful positioning of the motor that allows the cable to move freely.

mongoose01.jpg
Fig. 3:  The arrows point to the shifter cable exit point and the allowable bend.  Also visible is a wad of mastic tape I used as a makeshift bumper to help solidify the motor’s position during installation

To ensure you’ve got the motor positioned right, use your replacement shifter cable and just manually run it down into the housing.  If you can get it thru easily so it pops out the other end, you are good to go.  Once you get the motor positioned up so that it a) gives max ground clearance and b) does not interfere with shifting, its time to tighten it down fully.  You will use two clamping lock rings over the axle and bottom bracket.

Typically, you use a grey, thick inner lock ring to do the real work, and the thin polished black outer lock ring – which is essentially just there to look good and perform sort of like a jam nut.

IMG_20191008_174043.jpg
Fig. 4: Note the thick black Sharpie registration marks running along the top of the two outer rings and the bottom bracket.  If I ever look down and see those marks not lining up, something is slipping and needs attention from a torque wrench.

However, using an inner and outer ring requires two tools.  The inner lockring is physically covered by the outer lock ring, so you can’t see it, but if you look in your parts bag the differences are clear.  Pictured above is the same installation done with two inner lock rings stacked on top of one another.

The outer ring is essentially a trim ring.  Its there to look nice and serve light duty as a jam nut.  Using two inner rings means you can torque the bejesus out of each of them.  And speaking of torque, I use a 1/2″ torque wrench to put 100 ft lbs of torque on each of these two rings.  Yes, 100 each is well above the ‘official’ spec but it is proven to work.

A note on tools:  Cheapie Bafang wrenches made of thin steel will let you ‘get by’ with a basic tightening of these lock rings. They are widely available for roughly US$15.  I don’t recommend their use given the lack of ability to use a torque specification, and their small size.  Pass on these and your knuckles and palms will thank me, as will you when your motor does NOT loosen since you used proper tools.  To do the job right, you need to use something like the socket found here.  You want the ‘inner’ socket only unless you want to use the trim ring instead of the two inners.  Worth noting: This socket is also sold at Luna Cycle (they also make their own version that is intermittently in stock) and California Ebike.  Pair this up with the torque wrench of your choice.  Mine is this bad boy.

Step 3: the Chainring

The stock BBSHD chainring is solid steel and, well… its awful.  Not only is it the ugliest chain ring in the solar system, its design is known to drop chains and generally make owners’ lives miserable.  And it also weighs a ton.

IMG_20191008_174708
Fig. 5: the Disc of Death.  A medieval throwing weapon that coincidentally is also used as a Bafang BBSHD chainring.

You want to use one of the aftermarket alternatives out there.  Generally I buy Lekkie Bling Rings, where the 42T size (there are many available) with its 18.3mm offset is the size of choice (there are now Chinese clones of the Lekkie and they are so expensive its not worth taking the quality risk to save so few dollars) and works great to correct the chain line offset that comes from the BBSHD’s secondary housing sticking out as it does on the drive side.

However, for the Mongoose project I finally had a bike whose frame would allow me to use the other king of the BBSHD chainrings:  The Luna Eclipse.

As you can see in the gallery above, the Luna Eclipse ring has a serious inward offset.

24.8mm in fact, which brings it in more than 6mm close to the frame than the Lekkie can.  Add to this the unique, wicked narrow-wide tooth profile on the Luna that effectively means you will never, ever suffer a dropped chain.  Lastly, needless to say, it looks gorgeous.  But, the biggest deal is the enormous offset, which allows perfectly centered chainline… not easy to accomplish on a BBSHD build.

Step 4: Size and attach the Chain

I made this part difficult to illustrate because I put the bags on – so they don’t come off – before I took pictures of the chain and derailleur.  I’ll do my best to get through this without good pictures.

First and foremost, let me say that a great many builders get chain length completely wrong.  Unfortunately, a lot of them may have gotten their examples from bike manufacturers who skimped on chain length and did ‘good enough’ instead of ‘best’ to save a few bucks.  What do they get wrong?  They let the derailleur cage stretch forward; not understanding that it is the cage’s job to wrap excess chain… so let it do its job!  The only reason to stretch the cage is to use less chain (i.e. you are a bike manufacturer out to save a nickel or so).  By the way, stretching the cage also extends its springs, and which lasts longer… a device whose springs are at rest, or that are under stress?

Here’s just about the only published source I’ve seen that boils down how to do it right, although they don’t shout out to the high heavens what they are doing right that so many others get wrong.

I’ll lay out the process very briefly here:

  1. Shift down into your highest gear (your smallest cog, the furthest outboard from the frame)
  2. Run your new chain thru the drivetrain, so its unattached ends are on the underside of its loop, halfway between the front chainring and the rear axle (this is simply the easiest location to work with).
  3. Pull the unattached chain ends together so the rear derailleur cage is only slightly tensioned.  That means in the case of the Mongoose, where we have a long cage derailleur added into the mix, that the cage is pointed straight back behind the bicycle.  Believe it or not, thats how its supposed to work on the low gear.  The cage is wrapping as much chain as it can while still maintaining tension on the chain.  Here are low and hi gear shots taken at two different chain lengths on a different bike.  On the top-left-pictured setup, I was a little too generous.  But only by two links.
  4. Assemble your chain with your master link.

Forget about all the other tricks associated with determining chain length.  If you have a single front chainring, this is all you need to do.  Ensure there is sufficient tension on the little cog in back.  At this point you have added as much chain as you possibly can, so the big cog will take care of itself.  If you find you cannot wrap enough chain to make your big rear cog work, then that usually means you need to step up from a short cage to a mid-length, or from a mid- to a long cage.  Or just live with what you have because you physically can’t add any more chain.

Step 5: Cable Hookups

Sidebar: Why I used a triangle bag.
For this build, I chose to use a battery that is NOT hard surface mounted on the down tube of the bike (for now I am using the very safe, waterproof, crashproof LunaCycle Wolf Pack but I am not using its excellent magnetic mount).

I have decided to use a triangle pack simply because it hides a multitude of sins.  In particular it saves me the trouble of routing cables neatly and tidily across the frame, which in the case of the Envoy is made more difficult to do cleanly since there are no cable guides to piggyback onto, thanks to its internal cable routing.  The use of a dedicated ebike frame bag means I can just run my wires thru one hole and out the other without worrying about what they look like inside the bag.

A triangle bag also helps me with my goal of easy portability:  Long term I have a very specific small battery in mind that will sit inside of a cloth MOLLE pouch.  it will be a snug fit inside the triangle bag (thus no need for a hard mount), and when I am going into the store, I just unzip the triangle, grab the pouch, haul the battery out and set it in my shopping cart.  That internal pouch means my fellow shoppers are not looking at a bare high voltage battery with red wires sticking out one end.

Getting a triangle bag to fit your frame is often a challenge.  Getting one with ebike wiring cutouts doesn’t make things any easier.  Especially since the Envoy’s triangle is relatively large.  larger than pretty much all mass produced battery bags.  Except one.  The FalconEV triangle bag is one of the largest bags of its type and just happens to be a nearly perfect fit for this frame.  I’m using that bag here.

Hook up the Speed Sensor

I was pleasantly surprised to find I did not need to use an extension on the Envoy’s mid-tail frame.  However it was a close call.  The speed sensor must pass within 1/4″ of the magnet to be reliable.  To accomplish this I used a trick I have used with fat bikes.  I first wrapped the chainstay in a bit of silicone tape to make it grippy.  Then I used more silicone tape to affix a small rope/cable crimp sleeve onto my chosen spot on the chainstay.  The rounded exterior of the sleeve will mimic the chainstay when I stick the speed sensor to it, and finally a couple of zip ties in the prescribed loops on the sensor lock that little sucker down so it works perfectly and is going nowhere.

Connect the Battery Adapter

The motor comes with the ubiquitous red and black wire for its power feed, terminated by a pair of quasi-standard 40 amp Anderson powerpole connectors.  Actually, the Andersons are kind of dated, with an XT90 (and particularly the anti-spark XT90S) being a much more common, reusable and weather resistant connection to your 48v or 52v battery.  My kit from Luna Cycle came with another length of red/black wire, also terminated with a pair of Andersons on just one side and bare wires on the other.  The point of this ‘pigtail’ is to connect to whatever your battery wants as a connector.  Most likely that battery is going to have either another pair of Andersons attached to it, or a (hopefully female, for your sake) XT90S.  You use the Anderson pigtail to connect to another pigtail that uses whatever your battery wants.  Yes, this means you either need to a) solder or b) crimp together the two to make a proper connection.  If you have no skills in this regard, you can probably find a pre-made cable somewhere for an exorbitant sum.  Make sure it uses 8 or 10-gauge (thick!) wire.

(I Didn’t) Install the Gear Sensor

One way to trash your bike with a mid drive motor is to go hammer down on the throttle and then try to shift.  The bike will shift alright, with about 1000w of power behind it.  The sound that makes will tell you what a horrible thing you just did, and if you want to walk home some day with your snapped chain lying somewhere behind you on the ground, go right ahead and keep doing that.

There are many ways to keep this from happening.  Most of them old-school techniques developed before gear sensors came into common use.  Since I started riding before that time, and I already know you Don’t Do That by instinct, a gear sensor is optional for me.  Also since I am lazy I didn’t feel like wiring it in.  For others – especially for those new to mid drives, its probably best to use the sensor.

Here’s what you do:

  1. Attach the gear sensor to the motor – its the yellow cable end.  I am assuming you have one of the more modern BBSHDs and you don’t have to mess around with any sort of Y connector.  So we’ll pretend that problem doesn’t exist.
  2. Once the sensor is attached you now know where it can go on your frame.  See where it will line up best with your rear shifter cable, because you are going to fit it inline into/onto the cable.  So… pick your spot.
  3. Disconnect your shifter cable from your derailleur and pull the shifter cable out of the housing.  If you were following my prep steps above, you have already done this as I didn’t include a ‘replace the cable’ step there for this reason.
  4. With the shifter cable out of the housing, cut the housing at the place where you intend to install the gear sensor.  Place a shifter cable ferrule over each cut end of the now-separated cable.
  5. Run the shifter cable down the housing until it exits the cable where you cut it.  Push it out some more and then work it into the gear sensor, and out thru the other side.  Once you have it thru the sensor, run it in to the back portion of the separated cable housing and all the way back down to the derailleur.
  6. Cinch everything up so the sensor and the cable housing are all nice and snug against one another, and the now-inline sensor is placed as unobtrusively as possible.
  7. Reattach the derailleur cable.  Job done.
  8. Optional:  the gear sensor is nothing more than a little wheel inside of a box.  It senses when the cable is moving – when your shifter and derailleur are pulling on it.  As soon as the little wheel detects motion, it kills the motor and its torque for a split second.  That lets you can shift – even under full throttle – safely.  So… that little wheel can get crusted up with grit, and fail.  Early designs were infamous for this.  Modern ones seem to be free of the problem but be sure… spiral wrap that rascal in some silicone tape.  That seals out any possible crud ingestion so it will work forever without maintenance.

So, without the sensor here’s what I do instead:  While pedaling I …

  1. Stop pedaling and while not moving my feet
  2. Click my shift (always just one gear)
  3. Perform a single pedal rotation to make the shift happen (this is not enough to engage the motor with any worrisome level of torque) and stop pedaling.  the motor will engage and spin a little further, completing the shift as part of its brief power up/power down.
  4. Resume normal pedaling

That sounds like a lot but it takes about 2 seconds total.  Other folks have perfected the use of a brake lever as a clutch.  With some experience in the saddle, they can gently touch the brake lever just enough to activate the safety cutoff without also engaging the brakes.  Then they shift and release the lever.

Sidebar:  Magura MT5e ebike brakes have special levers that include a second hinge, mid-lever, that facilitates this brake-lever-touch cutoff method.

Wiring Harness Cable

A nice thing about the BBSHD is it has a single bundled cable that is meant to run up from the motor to the front of the bike, under the handlebars, where it splits off to connect up to the throttle, display and both brake safety cutoffs.  As clean as you can get given the multiple connections.  Just plug the harness cable into the motor, run it up and into the top rear of the bag, and out the hole in the front side.  The remaining dangly bits will connect right up to what you stick on the handlebars shortly.

On the Handlebars:  Display, Brake Levers and Throttle

These are pretty straightforward.  Place them where convenient for you, connect the color-coded plugs and job done.

Go Ride

Thats it!  You’re done.  I can guarantee you this:  It takes more time to write this article than it does to install the motor.  I think all in I needed only a couple of hours for the motor part, not counting all the extra work I made for myself swapping out everything else on the bike.

Author: m@Robertson

I'm responsible for the day-to-day operations at my place of business: Leland-West Insurance Brokers, Inc. We do classic and exotic car insurance all across these United States. I'm also an avid auto enthusiast, a born again cyclist (i.e. an ebiker) and participate in medium and long range CMP and NRA sanctioned rifle competitions.

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