Heater Motor Upgrade Supplement

by Rod Gramlich

Rather than chopping and hacking at my firewall to upgrade the heater motor in my CJ, I used a hole saw to cut the proper size hole. This technique saved me from removing my battery tray, but I did remove the passenger seat to make the work easier. Removing the passenger seat is relatively painless. The rest of the procedure is documented in Terry Howe's Heater Motor Swap article.

1. Cut a 1"x5"x1/4" thick piece of aluminum. Aluminum is preferred because it is soft and easy to work with. It will not grab on the hole saw once the blade makes it through to the firewall steel.
2. Mark the center of the bar and run it through with the hole saw pilot bit.
3. According to the measurements above, drill and tap the aluminum bar for two #10 machine screws on the ends of the bar.
4. Align bar as per illustration. Mark hole locations on the firewall and drill out for #10 screw clearance (~.195 bit size).
5. Slip the bar through the existing blower motor hole and hold it in place so that the two #10 screws can be inserted through the firewall from the inside. Screwed them into the tapped holes in the bar. Tighten the screws to pull the bar securely up against the firewall on the engine side.
6. Use a 3 1/4" hole saw and run the pilot bit into the pilot hole in the aluminum bar. Drilling from inside the Jeep, cut through the firewall. I would recommend a variable speed drill for this and never use the trigger lock on the power switch!! Hole saws tend to bind up and smash elbows and fingers.

The result is a nice and neat hole in the firewall that seals easily.