Mechanical PTO Maintenance Tips for Tree Care Equipment, Part Two

In Mechanical PTO Maintenance Tips for Tree Care Equipment – Part One, we outlined some key preventative maintenance steps to ensure you get the most from your chipper clutch. In this part we will discuss an easy—yet crucial—tip for maximizing uptime. 

The industrial Mechanical Power Take-off (PTO) is part of the mobile woodchipper powertrain and one of the pivotal components in the machine. The Mechanical PTO, or chipper clutch, is a self-locking, over-center clutch design that is mounted between the diesel engine and belt arrangement. In this configuration, the PTO functions as both a mechanical disconnect from the engine and a mechanical connection to the engine. When disengaged, it allows the engine to start and reach optimal operating conditions while unloaded. When engaged, it transfers the power from the engine to the belt drive to rotate the drum or disc. Keeping this piece of equipment running smoothly is key to preventing costly downtime.

PTO on mobile woodchipper
WPT Mechanical PTO on tracked chipper.

One important, yet often overlooked, aspect of PTO operation is engagement torque. The engagement torque is a measure of the amount of rotational force required to engage the PTO. This force is controlled by the clearance—or spacing—of the friction discs and center plates in the clutch pack. When a new PTO is purchased from the factory, the clearance is preset for optimal performance. As the chipper clutch is used and the friction discs wear, the clearance increases. To keep the clutch performing at best, the clearance must be adjusted to compensate for this wear. 

Checking the engagement torque is easy and only requires a beam-style torque wrench, standard socket, and few minutes time. Each mechanical PTO from WPT has a hex nut cast in the bottom of the operating handle that should be facing outward from the PTO. This hex nut is there to provide a point to attach the socket and torque wrench. With engine off and the torque wrench in place, engage the PTO like normal, but instead of using the operating handle, use the torque wrench to engage the power take-off. Observe the maximum torque required to engage the PTO. (Tip: This a great place to have friend help. One can engage, while the other watches the torque wrench). 

PTO Hex Nut
Hex nut cast for torque wrench adjustments.

Once the engagement torque is known, compare it to the values on the nameplate or in the manual. If the engagement torque is between the minimum and maximum, no further steps are needed. If the engagement torque is too low, that means the clutch pack may not be providing enough clamping force to keep the plates from slipping during peak loads. Engagement torque that is too high, could result in a clutch component damaged or a PTO that cannot be fully engaged. The latter can cause excess slipping and heat buildup that results in premature wear and even catastrophic failure of the clutch pack. Regardless, of whether it is too low or too high, adjustments will be needed. Refer to the PTO manual or watch our how-to video for the steps needed to properly adjust. 

PTO nameplate
Minimum and maximum torque values on PTO nameplate.

The frequency that the engagement torque should be checked depends on the number of engagements made each day and can even vary from machine to machine. In the beginning, or after a clutch replacement, it is best to check more often to develop a baseline for the standard rate of wear based on the usage. Once a baseline has determined, the engagement torque check should be added to the preventative maintenance program. A good rule of thumb is to check once a week. 

Checking the engagement torque on your chipper clutch is a great way to ensure the PTO will provide the performance you expect for years to come. The check only takes a few minutes, but that time spent is well worth it. Just ask anyone that has had to replace a clutch in the middle of job. So, grab a torque wrench and socket and go check that engagement torque. 

For more information on how to get most from your current PTO or for more information on the WPT Pilotless™ PTO visit or call 940.716.1971