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Baby Jeep Blog

An off-road journey from petrol to electric.

April 2020

It has been quite a while since my last post, and true to form I have been sidetracked, some which are my fault, and others that aren't. Between house building, fires, floods and hail, the Jeep has taken the back seat.

The good news is that I managed to get the Kostov electric motor attached to the Jeep manual transmission. Geoff O'tool from GT Tooling made a coupler, modified the Jeep motor plate to match the Kostov mounting pattern, and modified the 4.0L Jeep flywheel to fit inside the 2.5L bellhousing. As this was made from a combination of parts from different Jeep vehicles and motors, I didn't have a good reference for the "magic number", that is the correct distance from the adapter face to the flywheel flange. I knew what the distance was for the 4.0L engine, so I measured the length of the 4.0L bellhousing, and the 2.5L bellhousing, did some quick math, and settled on 60.75mm. I made a model using my 3D printer to test, and other than cursing the combination of metric and imperial bolts, it has been smooth sailing.

The bolts to attach the flywheel to the motor coupler are M12 but had to be 69mm, so I bought some 100mm long ones and cut them down. The thread on the Jeep flywheel was 3/8" UNC, so the tacho pickup bolts on the rear of the flywheel are 1/2" long, and on the pressure plate side on the front of the flywheel they are 3/4" long.

The tacho sensor is a Balluff BES01M8 inductive proximity sensor. It is mounted through a treaded hole directly behind the flywheel bolts so it can pick up the bolts as they spin. The specification sheet says that a maximum distance from the pickup is 2.5mm so I adjusted the distance to be a little over 1mm. A quick test with a multi-meter shows the sensor working nicely, picking up 6 pulses per revolution.

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