We were on the dyno at Kenny Duttweiler’s engine shop abusing a pump gas 383ci small-block Chevy at about 5,500 rpm when suddenly the dyno room filled with steam and water soon covered the floor. Once we shut the engine down and turned off the water, we discovered a brass freeze plug lying on the floor of the dyno cell. We were a bit surprised and more than a little embarrassed. Of course, what would have been worse is if this had happened at full speed on the drag strip dumping water under the back tires at 120 mph! Duttweiler said, “You probably installed that freeze plug with a large socket and a hammer, right?” This was exactly how we had beat that plug into place.

Duttweiler said that because brass is so much more expensive, the companies making these plugs have made them much thinner to save money. When the plug is installed with a large socket pushed into the bottom of the plug, this distorts the plug and pulls the walls inward, making for a very tenuous seal.

Our solution was to build a custom, stepped freeze plug tool that has a stepped mandrel a few thousandths of an inch smaller than the inside diameter of the freeze plug itself. This allows the tool to drive the plug from the face of the outside diameter of the plug, while supporting the inner walls of the plug, to prevent deformation.

The tool’s mandrel needs to be tapered so that when the brass constricts when installed into the block, that it does not pinch and capture the tool, which makes it difficult to pull the tool from the freeze plug. Our tool is double-sided aluminum fashioned by a machinist friend. The center on both ends is drilled and tapped to accept a long threaded steel handle that screws into the driver. A steel tool might be even better since steel won’t distort like our aluminum tool has over time.

We had our machinist buddy build a simple aluminum driver with two ends — one for small-block and one for big-block freeze plugs.