How to mate a Nissan leaf electric motor to a manual transmission: The Motor coupler

The Nissan leaf electric motor (em61 and em57) are great motors for EV conversions. They are easy to obtain, relatively inexpensive, and powerful! The only catch is how do you swap one into a different vehicle?

Nissan Leaf motor (em57) and coupler

Part 1: The motor coupler

The Nissan leaf motor has a splined output shaft. The splines are designed to transfer torque from the rotor, to the leaf’s gearbox. But how do we connect the leaf motor to a different gearbox? With a motor coupler! I sell blank Nissan leaf couplers with the right spline geometry to ensure there’s a reliable, direct connection between the leaf motor and manual gearbox of choice.

Why a direct, clutch-less connection? more on that later.

blank Nissan leaf coupler

The couplers come with the leaf spline on one end, and are blank on the other. In order to use the coupler, some machining and welding is needed! This is a simple job for anyone with a lathe and a TIG welder. Most machine shops can do this work for you in about an hour!

dimension of the blank leaf coupler

Machining:

step 1:

Remove the splines from the clutch disk.

clutch disk and blank leaf coupler

with a drill press or grinder, remove the rivets holding the clutch assembly together. seen in the photo above, there was only 3 rivets to cut down to get the clutch center.

clutch disk center removed from the clutch

cut away any excess material, leaving the core clutch center.

clutch center cut down ready to be turned on the lathe.
whoops! made some unnecessary cuts into the clutch center!

step 2:

Determine how much backspacing from the motor to the gearbox there is. This is important as you want the coupler to mate fully with the splines on both motor and the gearbox. This is to ensure the torque transfer is distributed equally across both splined faces.

step 3:

Chose how much material to machine off the clutch center and how much to machine out of the blank end of the leaf coupler. The more material left on both parts, the better.

Ensure that the clutch center will recesses into the blank leaf coupler as much as possible. This will maximize the friction surface area, resulting in a stronger coupler.

machining the clutch center down

Add chamfered flange on the clutch center, this will give a larger surface area for TIG welding.

Machined down clutch center, with a chamfered flange

step 4:

Machine the blank end of the leaf coupler to be 1/2 thousands of a inch smaller than the outside diameter(OD) of the machined clutch center. Resulting in a interference or “shrink fit”

blank end of the leaf coupler bored out to 1/2 thou smaller than the OD of the machined clutch center

chamfers on both the clutch center and blank leaf coupler

step 5:

Heat up the blank leaf coupler or freeze the machined clutch center. Press the machined clutch center into the bore of the leaf coupler. The heat will cause the leaf coupler to expanded/the cold will cause clutch center to shrink, giving space for the machined clutch center to press into place, with relative ease.

With a strong enough press, and a beveled leading edge, press fitting may work without any heating/cooling!

leaf-to-gearbox coupler all pressed together.
ready for some TIG welding!

Make sure the parts are trued up, and concentric, as the coupler may spin up to 10,000 rpm!

TIG welding:

The leaf coupler is made from 4140 chromoly steel. This means it’s an alloy steel with some chromium and molybdenum in it, hence the name “chromoly.” These elements, along with its high carbon content, make it very hard and strong compared to regular steel. These properties make it perfect for a motor coupler! But makes it a little more fickle to weld compared to regular steel.

Because 4140 is so hard, when its heated up unevenly or too quickly(like when welding), it can crack. To avoid cracking, preheat 4140 before welding.  This is done to slow the rate the part cools after its been welded. This reduces the chance of embrittlement, which leads to cracking.

-pre heat for material up to 1/2″ thick 400-500F [205 – 260C]

-use filler material ER80S-D2

-use a low hydrogen electrode

Hydrogen and carbon put together cause some problems, we can’t get ride of the carbon, but we can minimize the hydrogen with a low hydrogen electrode.

The longer the 4140 takes to cool down, the better. This not only reduces the chance of embrittlement but also gives more time for hydrogen to escape, reducing hydrogen induced cracking.

Next:

How to mate a Nissan leaf electric motor to a manual transmission: Part 2, Adapter plates

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