3 June 1977
PTO OVERSPEEDING PROBLEM
1. Field users are reporting that the CCE-IHC 20 Ton Dump Truck PTO, for the dump body hydraulic hoist system, is
being damaged by overspeeding of the engine during the hoist cycle. The PTO and the dump body manufacturers warn
that the engine foot throttle should be depressed only far enough to reach 1500 RPM engine speed while dumping. The
engine is governed at 2100 RPM (about 2350 RPM during no load overrun). Therefore, it is in the hands of the dump
truck operator as to whether or not he operates his CCE-IHC dump truck so as to not damage the PTO and hoist pump.
2. Overspeeding of the PTO driven components has been a commercial user problem for many years. These users
employ two principal methods of achieving limited engine speed for PTO operation as follows:
a. Marking Method: Label the tachometer dial at the maximum recommended engine speed of the PTO/pump
component supplier with the words "MAX PTO" and then mark with a red colored band on the tachometer bezel from this
engine speed limit on up to the maximum engine speed reading of the tachometer. (For the CCE- IHC dump truck
application, the label would be applied near the 1500 RPM reading of the dial and the red band would be applied between
1500 RPM through 2100 RPM).
Governor Method: Install a Manual Variable Speed (MVS) PTO governor on the engine fuel pump control lever.
The marking method works satisfactory for some users. Its simplicity of application on the truck is the
major benefit. The major disadvantage lies in the fact that some drivers don't observe the engine speed limit for PTO
operation and overspeed damage to PTO components still occur. The Marking Method (see Figure 1) involves applying
the words, "PTO MAX" on strips of self-adhesive, red tape and after cleaning, sticking this label at the maximum
recommended engine speed limit of the tachometer. The tachometer bezel is then painted with red paint from this limit
around to the maximum engine speed reading. The users train the drivers not to operate the engine in the red band of the
tachometer, whenever the PTO is engaged. This labeling and banding has proven more satisfactory than a separate
decal on the instrument panel. Some drivers ignore the markings and still overspeed the PTO System.