If you walk through almost any excavation site in the world, you will see an operator or a mechanic jamming a long pry bar under the excavator track frame, lifting the chain off the top roller, and pushing down to see how much slack there is. It is the most common, universally accepted method of checking track tension. It is also completely wrong and is the leading cause of premature track chain and idler bearing failure.
When you use a pry bar, you are applying a massive, localized point-load to the track chain. You are bending the chain links around the pry bar, not measuring its natural droop. Furthermore, operators almost always leave the tracks way too tight. An excavator track should have a specific amount of sag-usually between 1.5 to 2.5 inches, measured precisely from the bottom of the grouser tip to the top of the track pad, right in the middle of the track frame, with the machine sitting on flat, level ground.
If the track is too tight, the chain cannot flex as it goes around the front idler and the rear sprocket. The tension is transferred directly into the pins and bushings of the track chain, grinding them into dust. Worse, the extreme tension is transferred straight into the bearings of the front idler, causing them to overheat and seize. The correct tool is a simple tape measure. If you are using a pry bar, you are guessing, and you are shortening the life of a $15,000 track chain by thousands of hours. Loosen the grease valve, let the tension completely off, roll the machine backward a few feet to let the chain settle naturally, and then measure the sag.
