Adding a Motor to a Mountain Bike

Fitting a motor to a mountain bike makes for an interesting project and an opportunity to overcome problems encountered along the way. It may also be a little more economic than purchasing a ready made ebike.

The motor I fitted to my mountain bike was Tongsheng's TSDZ2. I choose this over the other popular mid mounted motor (the Bafang BBS02) because you have to apply pressure on the pedals for the motor to run rather than just spinning the pedals. There are also motors which are in the front or rear wheel but its generally considered these are not as good as mid mounted motors.

On the face of it the economics of fitting your own motor to an existing mountain bike appears reasonable compared to buying a factory electric bike but when you include other costs such as for the special bike tools required it may not be so clear cut.

To my surprise the box containing the motor arrived after only a few days, I thought it might have taken a lot longer as it was supposably coming from China. My guess is the company I purchased it from had a local fulfillment center.

The motor was will packed and complete. It came with a basic instruction booklet on fitting the motor. No instructions on removing the crank were included and this is in keeping with the market who are likely to be interested in the motor: People who like working on projects and are willing work things out as they go along. If that's not you, no worries, you can always purchase an electric bike from a bike shop and that's not such a bad thing as fitting a motor yourself does have a few unknowns, such as 'What if it doesn't fit'?.

You will need some specialized bike tools to be able to remove the existing crank from your bike. As luck would have it the local Aldi supermarket store had a set of bicycle tools for sale as one of it's 'specials' for a reasonable price so I got them. I was a little worried if the quality would be good enough but figured they would probably do for what would likely be a one off job.

The first thing I did was to take off the peddles. These came of easily enough. From memory it was 'lefty loosie, righty tighty' but you have to be a little careful as there is a left crank arm and a right crank arm and they can easily be mistaken (more on this later) The bolt on the crank was then unscrewed.

Removing the crank requires a specialized 'Crank puller' I had heard of people stripping the tread when the tool was not up to scratch has or hadn't been screwed in enough. I had considered buying a branded product for the job but stayed with what I had. I was was sure to screw the bottom nut in well using a wrench to seat it down, before using the top bolt to pull the crank out. It came out easily enough. This may have been a different story it was a little corroded. I started a little at a time to and went slowly to avoid stripping the thread.

There was ring each side holding the bottom bearing in place. A special bike tool was required to remove it.

The bearing came out easily enough. There is value in keeping bikes out of the rain so parts don't become corroded and difficult to work on.

As the chain had been left around the derailleur, following the removal of the big sprocket, I removed the derailleur and the front gear leaver. These aren't required as the motor only has one big sprocket on the front ring.

My bike has internal cables and they come out under the bottom bracket - where the motor will be fitted, some people have found a problem with clearance and I wondered if it would be a problem with my bike. Turns out they could just fit.

As the chain was threaded through the derailer it needed to be removed by 'breaking it'. I watched the you tube clip on it. Removing a chain. It can be done quite simply if the chain has a connection link. Looking at my chain I saw it did have an 'easy link' which are apparently easy to open. Sometimes this can be done by hand or with special pliers. Mine wouldn't come undone by hand and I didn't have the special pliers, I tried long nose ones but they didn't fit. What I did have was a 'chain splitter' tool. This wasn't that will made and a little off canter and so I had to file the point a bit so it would line up with a rivet.

In hind sight it would have been easier to have brought the tool required. But I wanted to get on with the installation job.

So far, so good, I thought. Then I tried to slide the motor arm into the bracket open, it wouldn't fit. 'How can this be?' On inspection it looked like after the tread in the bracket ended the hole went a little narrower. So a quick internet search came up with the suggestion to use a 'Dremel' rotary tool to enlarge the hole. I had a similar rotary tool and took to it with a carving attachment. Seemed to work but was making some groves. So I went and brought some more attachments. On my return they wouldn't securer into the rotary tools' collar. Following another search on line, I read of a suggestion to use a brake cylinder hone tool to enlarge the hole.

Having purchased a honing tool, I gave it a go. This had the advantage of fitting into my electric drill. After using it for five minutes I could see that while it had a level abrasive action, it wasn't doing much. After all it is a 'honer' not a cutter.

Looking through the Dremel attachments I had purchased the day before, the sanding drum caught my eye. Tried fitting it to my drill with only about 1/4 inch in, to give enough reach. This turned out the be the 'goldy locks' solution as it was 'just right'. It cut level and had reasonable bite into the aluminum.

Tried to fit the motor shaft into the hole again and while it would go in a bit more, it was still binding. I had no way of knowing where this was and realized I could easily make the hole too big in some parts if I wasn't careful.

I needed a way to gauge where in the hole it was binding.

Turn's out I had the solution in the bathroom. As applying some toothpaste enabled me to gauge where in the hole it was binding and where there was free travel. Afterwards I cleaned the paste off well.

Success! The motor shaft could now travel through the shaft.

Next was to attach the plate with 2 bolts and spacer washers.

Then the outer ring went on, using the special wrench, which had been included in the kit. This is tightened really well (40N). I had thought of using some blue lock tight with it but decided to hold off a bit as going by experience it could need to be loosed before the install was completed.

The motor also has a securing bracket to Install. On my bike it wouldn't fit. I could have probably left it off and just kept an eye the securing ring and retightened it regularly.
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However I figured it could be fitted by drilling and tapping another hole.
To know where to drill, I did the toothpaste again and placed a little paste on the end of the bolt to see where to drill a new hole.

Using a punch the centre for the hole is marked. Then a smaller sized hole acts as a pilot hole, ft
Then a 7 mm drill made the hole for the 8mm tap.

I purchased a cheap tap set and used a 8mm tap to tap into the 7mm hole. The hole needs to be a bit smaller so the tap can cut into the metal and make the threads.
With the new taped hole made it enabled the supporting bracket to be fitted.

Now, I have heard there is a left and right cranks as the thread in in peddle is reversed between them. This is so when you are cycling along your leg action is tightening the pedal rather than loosening it.
Anyway, when I came to fitting the cranks I looked for marking for the left and right crank and couldn't see a difference. So grabbed one and installed it on the left side. It fitted easy enough.

Now, fitting the right crank wasn't so easy. The arm didn't fit snuggly over the connector which I put down to just needing to be bedded in with the bolt. After tightening the bolt a bit I stripped the thread from the end of it. Rather than re-examining both arms, I pressed on. Checked why it wasn't sliding on and came to the incorrect assumption that it hadn't been made that well and the hole needed to be enlarged.

I took to the inside of the crank with a small square file and after much filing and checking enabled it to slide onto the shaft and be bedded down with the bolt.
That evening I had another think and took a photo of the marking on the cranks to confirm they were the same... on closer examination one said '170LT' and the other '170RT'. I had swaped them over! This is likely to mean the paddles could work themselves off after use. I will kept an eye on them and have ordered a replacement (left) crank. When it arrives I will try swapping them over again. The availability of space parts is an advantage of the retro fitted ebike.

A speed scenor was fitter with a couple of cable ties. The magnet fitted to a spock is aligned with the arrow and is about 10 -15 mm away.

There was a small cap over the lead it fits into, which had to be removed and it has the same number of pins.

The cable from motor to display may at first glance look similar to the speed sensor but it has a different number of pins and a different fitting.
The display was fitted to the handle bars by removing the bolts, clipping the display over the bars and then reattaching the bolts.

Brake leavers are given with the motor which will stop the motor when the brake leaver is pulled. My bike had cable brakes. There is also a version for hydraulic brake leaver.

I later fitted Hydraulic brakes to the bike, without fitting a cut out to them. Haven't had any issues but when I stop I keep the brakes on and take my feet off the pedals.

The chain was placed around the front and rear sprockets and rejoined. The front sprocket is larger than what was there and while I did manage to fit the chain over it and use the rear gears, it looks a bit short and so will buy a longer, heavy duty chain.

As can be seen, the 'rejoined' link doesn't look like a good join and this was born out on the second test run when the chain came off. Best to replace the link with an 'easy link' than try to join with the chain breaker.

As the cables from the motor looked to be quite near the chain, I used a cable tie to pull them out of the way.

I took the bike for a spin to check nothing was rubbing.

Hopefully, the ride up the hill will be easier when the battery arrives....

Battery arrived a week after the motor. Fitting it on the frame was not as straight forward as it could have been. Finally managed to just fit it in with a bit of filing on the base.

The battery came with a different connector to the motor. Requiring the connector from the motor to be removed and the joined to the connection supplied with the battery. Purchased a clamping tool and joiner to achieve this.

With the addition of the battery connected to the motor the bike was much easier to go up the hill.

With the motor and battery being added to the bike its value has increased and it will have become more attractive to thieves. While a better lock has been ordered, in the mean time I remove the battery to make it less attractive to thieves when parked. I got a folding flat bar lock, while not a good as a 'D' lock it looks bolt cutter resistant and is easy to keep on the bike.

I installed a stand which is providing useful. While on a ride a screw came loose and part of it fell off and the replacement I tightened the screw well and will check on it.

Another tip is to get a triangular door block to keep self closing doors open and use it when wheeling the bike though them.

As I had got the crank arms mixed up, one of the peddles came loose and needed tightening, really should swap them back round.

The main locking nut, securing the motor came loose on a ride. By tightening it by hand and peddling lightly I finished the ride. I will use some lock-tight on it so it doesn't come loose in future.

I replaced the cable disk brakes with hydraulic ones. I choose Shimano M6100 after reading some reviews but the cheaper MT 200 ones would have also worked just fine. I enjoy using the hydraulic brakes more than the cable ones, easier to use, but stopping distances is similar.
https://www.instructables.com/Cable-Vs-Hydraulic-Disc-Brakes/
Another improvement was replacing the handle grips with ones with palm rests - well worth while. A rear pannier carry has recently been added to carry shopping. It carries a couple of 6 packs with ease.

After using the ebike for 300 kms I noticed the battery had come loose. On inspection this was due to part of the mounting breaking a little. Not a great idea to use a cast piece where high tensile strength is required. It was fixed by adding a larger washer and further supporting the battery with a cable tie.

Fitting an electric motor has proved to be an interesting project and I find I use it when shopping but on a recent 350 km bike tour I took my normal bike as on the longer Km days I didn't want to be peddling an electric bike with a flat battery.

For a couple of months I was using the electric bike all the time. I now use my normal, commuting bike, about half the time as it's lighter to ride and I feel better from the exercise riding it.

The original big sprocket before the conversion was smaller than the one which came with the kit and so I wanted to see how the bike went with a smaller front spocket for hill climbing as I had a mountain bike event coming up. I purchased a 38T and a 30T with an adapter and fitted them. The idea been to manually move the chain between sprockets when required. This is expected to give more climbing power on an upcoming mountain bike trip.

While I purchased the adapter and 2 sprockets, I would probably been better buying one which used the existing centre. https://a.aliexpress.com/_mO7MxUa This has 5 bolt holes. My replacements have 4, hence the use of the adapter.

I have used the new sprockets on a couple of short trips and so far no problems. I have left this on but haven't had the need to use the lower sprocket - maybe I will if I take it on a fire trail but I have found that after a year of use and clocking up 650 km, I manly use the bike as a 'work horse' to do grocery shopping.