1983 Porsche 911 SC Targa

Tuesday, June 12, 2012

Joining the Motor and Transmission

This is one of the major milestones of the project. I could not have completed this step without the help of my friend Pat, who is a talented joke teller and equally good machinist. Some of the parts I ordered needed modification, and with Pat’s help, we modified them to make everything fit together properly.  Thanks Pat.

The goal is to build up the motor to make it look like the gas engine block. The important parts are the hub, which spins with the crank shaft, and the mounting flange for the transmission.

The first part to go on the motor is the taper lock bush. This piece has a slight taper, and as you bolt it together with the hub, the taper provides a clamping force that grips the motor shaft. This is one of the most secure ways to mount a hub to a shaft. I used a dial indicator to keep the face of the hub square to the motor shaft, as I tightened the mounting bolts (marked 1, 2, and 3 in the photo). Any error here will cause the flywheel to wobble and the vibration will be annoying and cause excessive wear in the drive train. I was able to get the wobble down to 0.003” (75 microns), and run out down to 0.002” (50 microns).

Next the adaptor plate is installed. This mechanically provides a surface to bolt the motor to the transmission.
The flywheel is bolted to the hub.

The clutch is centered on the flywheel with a special alignment tool.

Then the pressure plate is added. The clutch is squeezed between the flywheel and pressure plate, and transmits power from the motor to the transmission. When the clutch pedal is pressed, the pressure plate is pulled away from the clutch disk and the motor and transmission are de-coupled, making it easier to change gears.

Here is a video of the clutch spinning up:

The motor is then mated to the transmission.

 Applying 12 volts to the motor spins the output shafts of the transmission: