Following a complete overhaul or any major repair that uses replacement piston rings, pistons, or bearings, for example, the engine should be run-in on a dynamometer prior to release for service.
The dynamometer is a device for applying specific loads to an engine to determine if the engine will perform to published specifications and to permit a physical inspection for leaks of any kind. It is an excellent method for detecting improper tune-up, misfiring injectors, low compression and other malfunctions, and may save an engine from damage at a later date.
The operating temperature within the engine affects the operating clearances between the various moving parts of the engine and determines to a degree how the parts will wear.
Thermostats are required to control the coolant flow and to help maintain a constant engine temperature. Therefore, ensure that they are in place and fully operative or the engine may overheat during the run-in. Overheating may result in engine damage. Furthermore, a deaeration line must be installed in the uppermost portion of the engine to prevent any overheat problems during run-in.
The rate of water circulation through the engine on a dynamometer should be sufficient to avoid having the engine outlet water temperature more than 5.6 C (10 F) higher than the water inlet temperature. A 5.6 C (10 F) rise across an engine is recommended; however, an 8.3 C (15 F) temperature rise maximum is permitted.
A basic engine includes only those components actually necessary to run the engine. The addition of any engine driven accessories will result in a brake horsepower figure less than the values shown in the Engine Run-In Check. The fan and battery-charging alternator typify accessories not considered on the basic engine.
Since the DDEC system requires a source of electrical power to operate the Electronic Unit Pump, all DDEC equipment should be connected and operating properly. In addition, a fully charged battery must be connected to the system. Refer to OEM guidelines.
In situations where other than basic engine equipment is used during the test, a proper record of this fact should be made on the Engine Test Report. The effects of additional equipment on engine performance should then be considered when evaluating test results.
The function of the dynamometer is to absorb and measure the engine output. Its basic components are a frame, provisions for engine mounting, the absorption unit, a heat exchanger, and a torque loading and measuring device.
For accurate dynamometer readings during engine run-in, the chassis dynamometer room must be properly ventilated. See Figure 25315 .
California Proposition 65 Warning
Diesel engine exhaust and some of its constituents are known to the State of California to cause cancer, birth defects, and other reproductive harm.
The engine is connected through a universal coupling to the absorption unit. The load on the engine may be varied from zero to maximum by decreasing or increasing the resistance in the unit. The amount of power absorbed in a water brake type dynamometer, as an example, is governed by the volume of fluid within the working system. The fluid offers resistance to a rotating motion. By controlling the volume of water in the absorption unit, the load may be increased or decreased as required.
The power absorbed is generally measured in torque (lb ft) or N m on a suitable scale. This value for a given engine speed will show the brake horsepower developed in the engine by the following formula, see Figure 21483 .
Formula for Brake Horsepower Developed in the Engine
Some dynamometers indicate direct brake horsepower readings. Therefore, the use of the formula is not required when using these units.
During the actual operation, all data taken should be recorded immediately on an Engine Test Report, see Figure 25775 .
Certain instrumentation is necessary so that data required to complete the Engine Test Report may be obtained. The following list contains the minimum amount of instruments and the proper location of the fittings on the engine so that the readings represent a true evaluation of engine conditions.
In some cases, gages reading in pounds per square inch are used for determining pressures while standard characteristics are given in inches of mercury or inches of water. It is extremely important that the scale of such a gage be of low range and finely divided if accuracy is desired. This is especially true of a gage reading in lb/in.2 , the reading of which is to be converted to inches of water. The following conversion factors may be helpful.
Gage reading = (lb/in.2 ) x 27.7 inches of water
Gage reading = (lb/in.2 ) x 2.04 inches of mercury
Before starting the run-in or starting the engine for any reason following an overhaul, it is of extreme importance to observe the instructions; see "Preparation for a First Time Start:'' refer to section . Failure to follow instructions could result in engine damage.
Use the following procedure for preparation of engine run-in. See Figure 25775 , part A.
Use the following procedures for engine run-in:
All engines should be operated at idle for at least one minute after starting to assure oil supply and pressure to the turbocharger bearings. Inadequate lubrication will result in bearing damage.
Engine Test Report Form
Note: Allow the engine to idle at least 3 minutes in order for the turbocharger to cool and reduce speed before shutdown.
After all of the tests have been made and the Engine Test Report is completed, see Figure 25775 , Part D., the engine is ready for final test, see Figure 25775 , Part E. This portion of the test and run-in procedure will assure the engine owner that his engine has been rebuilt to deliver factory rated performance at the same maximum speed and load which will be experienced in the installation.
If the engine has been shut down for one hour or longer, it will be necessary to have a warm up period of five minutes at the same speed and load used for warm-up. If piston rings or bearings have been replaced as a result of problems during the warm-up, the entire run-in must be repeated as though the test and run-in procedure were started anew.
All readings observed during the final run-in should fall within the range specified in the "Operating Conditions'' ( refer to section ) and should be taken at full load unless otherwise specified. Following is a brief discussion of each condition to be observed.
The following steps are necessary to complete the final Engine Repair Schedule.
Note: While making the final run-in, the engine should develop the maximum rated brake horsepower indicated for the speed at which it is operating. If this brake horsepower is not developed, the cause should be determined and corrections made.