Since the engine has just been reconditioned, this run-in will be a test of the workmanship of the serviceman
who performed the overhaul. Minor difficulties should be detected and corrected so that a major problem will
After performing the preliminary steps, be sure all water valves, fuel valves, etc. are open. Also inspect the
exhaust system, being sure that it is properly connected to the engine. Always start the engine with minimum
After the engine starts, if using a water brake type dynamometer, allow sufficient water, by means of the control
loading valves, into the dynamometer absorption unit to show a reading of approximately 5 lb ft (7 Nm) on the
torque gage (or 10-15 HP on a horsepower gage). This is necessary, on some units, to lubricate the absorption
unit seals and to protect them from damage.
Set the engine throttle at idle speed, check the lubricating oil pressure and check all connections to be sure
there are no leaks.
Refer to the Engine Test Report sample which establishes the sequence of events for the test and run-in, and
to the Basic Engine Run-In Schedule which indicates the speed (rpm), length of time, and the brake horsepower
required for each phase of the test. Also refer to the Engine Operating Conditions Specifications which
presents the engine operating characteristics. These characteristics will be a guide for tracing faulty operation
or lack of power.
Engine governors in most cases must be reset at the maximum full-load speed designated for the run-in. If a
governor is encountered which cannot be adjusted to this speed, a stock governor should be installed for the
After checking the engine performance at idle speed and being certain the engine and dynamometer are
operating properly, increase the engine speed to half speed and apply the load indicated on the Basic Engine
The engine should be run at this speed and load for 10 minutes to allow sufficient time for the coolant
temperature to reach the normal operating range. Record length of time, speed, brake horsepower, coolant
temperature, and lubricating oil pressure on the Engine Test Report.
Run the engine at each speed and rating for the length of time indicated in the Basic Engine Run-In Schedule.
This is the basic run-in. During this time, engine performance will improve as new parts begin to "seat in".
Record all of the required data.
C. BASIC RUN-IN INSPECTION
While the engine is undergoing the basic run-in, check each item indicated in section C of the Engine Test
Report. Check for fuel oil or water leaks in the rocker arm compartment.
During the final portion of the basic run-in, the engine should be inspected for fuel oil, lubricating oil, and water
Upon completion of the basic run-in and inspection, remove the load from the dynamometer and reduce the
engine speed gradually to idle and then stop the engine.
D. INSPECTION AFTER BASIC RUN-IN
The primary purpose of this inspection is to provide a fine engine tuneup. First, tighten the cylinder head and
rocker arm shaft bolts to the proper torque. Next, complete the applicable tuneup procedure. Refer to Engine