Adding Flywheel Mass for Engine Torque

An object in motion tends to stay in motion, and the more mass the object has the more it tends to stay in motion. This is why we upgraded the flywheel on a four-cylinder Jeep YJ Wrangler with a heavier one, to help keep it spinning.

The Wrangler four-cylinders are everywhere these days, and for dirt-cheap (or at least cheaper than their grunty six-banger brethren) the tough little 2.5L engines offer a great platform for a beginner 4x4. However, when you really lug these engines down off-road they can stall and stumble if not adequately geared for big tires.

The Jeep 2.5L engine was only rated at about 120 hp and 130-some lb-ft of torque, but when under the hood of a stock Jeep YJ or TJ it works reasonably well. Bigger tires sap that power, as do heavy accessories like bumpers and winches.

The Jeep 2.5L engine was only rated at about 120 hp and 130-some lb-ft of torque, but when

We took a ’95 YJ to Tri-County Gear, where they offer a flywheel weight specifically for the Jeep 2.5L. This added weight is designed to give the thrifty 2.5L extra grunt, as the spinning mass helps keep the engine chugging along when down low in the rpm’s.

Is It Different?
Our YJ project is a major back-burner build: a little here, and then it sits for months, then a little there as time and money allows. As such, we’re still not wheeling it regularly. However, our back-40 testing has been nothing but grins with the new heavier flywheel. The Jeep is a little tractor, idling up and through ditches where it used to require plenty of clutch slipping. The added weight isn’t even noticed on acceleration, a concern we had. We’re always interested in lower gearing, and to do it again we’d consider and upgrade to an old granny gearbox like an SM420, or 465 for strength and crawl control. However those boxes add weight, so we’ll run the AX5 until it blows (not uncommon).

Between the engine and the clutch is the flywheel, a heavy piece of cast iron. Notice the multiple teeth on the flywheel. The small teeth are for the starter; the larger teeth are to activate the crank position sensor and help time the ignition and fuel injection. The bottom flywheel with 40 teeth is for a throttle body 2.5L, while the top flywheel with fewer teeth is for our multipoint EFI 2.5L.
Between the engine and the clutch is the flywheel, a heavy piece of cast iron. Notice the
The additional 9-pound flywheel weight from Tri-County Gear (right) may not seem like much, but when running a small engine every bit of added mass can make a difference. Before assembly the flywheel should be cleaned and checked for cracks or other damage.
The additional 9-pound flywheel weight from Tri-County Gear (right) may not seem like much
Before the weight can be installed the threaded holes in the flywheel need to be drilled out. This allows the threaded studs to pass through the flywheel.
Before the weight can be installed the threaded holes in the flywheel need to be drilled o

The threaded studs on the flywheel weight pass through the flywheel as the weight rides on the engine side of the flywheel. This will be where the clutch bolts in place.
The threaded studs on the flywheel weight pass through the flywheel as the weight rides on
With the flywheel out, the pilot bearing or bushing should be replaced. A high-mileage clutch may also be due for replacement at this time since the transmission and transfer case are already removed.
With the flywheel out, the pilot bearing or bushing should be replaced. A high-mileage clu
With the flywheel weight installed and back on the engine, it’s a simple reassembly of clutch, transmission, and transfer case. Our stock AX-5 transmission in this beat ’95 YJ isn’t the strongest trans, but it’s fine for beginner wheeling with the Tera low gears in the transfer case and 4.88s in the diffs.
With the flywheel weight installed and back on the engine, it’s a simple reassembly of clu