Motor Adapter

The adapter connects the electric motor to the old gas car transmission. My adapter has these missions:
That last bullet is generally not considered on street vehicles, but is a requirement for some types of racing.

Here are a few pictures of the motor and tranny that need to be coupled together with the adapter.

Original motor flywheel
This is the original motor's flywheel. Note it is dished into the motor, and is not flat.

Motor frontMotor toptrans topTrans front
The 2nd picture is a nice shot of the taperlock coupler I bought from It shows how the flywheel sticks out a fair distance from the motor. Since the flywheel is dished and the transmission pilot shaft goes pretty deep into the flywheel, it would be tough to get it much closer and keep the stock electric motor shaft, stock flywheel, and stock transmission shaft.

trans plus motor
So close, yet so far!

Most adapters are made from aluminum. I am making mine from 1/4 inch steel. There are several reasons for this choice:
The adapter will be made from 4 main pieces:
Exploded side view of motor, motor plate, spacer, transmission plate, scatter shield, and transmission.

Exploded side view. The motor plate, spacer, transmission plate, and scatter shield will be welded together one assembly, called the adapter. The transmission fits inside of the scatter shield. The motor and transmission are bolted to the adapter. The flywheel and pressure plate are not shown.

Here are a couple of pictures showing the motor plate, spacer, and transmission plate after being rough cut:

Motor plate, spacer, and tranny plate  Tranny plate, spacer, and motor plate stacked

The last picture is the arrangement the finished product will have. Some machining and welding is needed.


I used emachineshop for my technical drawings (

Machinist's drawing for spacer.

The diameter of the spacer was chosen so it would go outside the motor mounting bolts, but fit inside the tranmission mounting bolts. Its 3 inch nominal spacing will be machined down a bit to perfectly space the flywheel from the transmission, so the clutch will work well.

3d CAD view of spacer.

Here is the spacer before it was ring rolled:

Spacer before ring rolling

To bend the flat strip of metal into the metal hoop, I used a ring roller I built, I had to turn the ring roller main bolt a fraction of a turn at a time, so it took maybe 20 passes and about 1/2 hour to roll it as pictured below:

Motor spacer

I was quite happy it came out so circular, and that the ends matched up so well. These next two pics just show my welds.

Spacer outer weldSpacer inner weld

Motor Plate

Here are my CAD drawings for the motor plate:

Motor plate cad 2d

Motor plate cad 3d

The 4 inch hole in the center of the plate is one of the crucial dimensions. It fits over a 4 inch centering ring on the electric motor. If this fit is loose, the motor shaft and clutch won't line up, and may vibrate or wear the bearings quickly. Once this plate is bolted to the machining rotary table, it won't be removed until the whole adapter is done. This will insure that the 4 inch centering hole stays concentric with the rotary table and other parts of the adapter.

This plate was cut using a plasma cutter, and a cutting guide to cut in a smooth circle. Here are a couple of pictures right after the plasma cut:

Motor plate after plasma cut  Motor plate leaning on spacer

Transmission Plate

CAD drawings:

Transmission plate CAD 2d

Transmission plate CAD 3d

That raised ring is another crucial part. This centers the adapter to the transmission. This ring will be welded on, and then machined by turning the rotary table. This will insure this ring is concentric with the motor plate 4 inch centering hole.

Here is the transmission plate right after being cut from a big steel plate with a plasma cutter:

Transmission plate  Transmission plate leaning on spacer

Scatter Shield

I haven't done drawings yet, but this will be a 1/4 x 3 inch strip similar to the spacer. One complication is the starter mount sticks out, so it will get a special piece to go around it.