A Kubota diesel engine for rebuild - Engine Builder Magazine

A Kubota diesel engine for rebuild

Engine Builders: If you are considering a Kubota diesel engine for rebuild, the following specifications regarding compression pressures will be helpful. For your installer customers, this information will be useful in engine diagnosis.

To obtain an accurate value of cranking compression, the engine should be operated until normal operating temperature is reached. If an engine will not start, the cold cranking compression value can be used but it will be 3-10 percent lower than a hot reading.

Kubota provides seven different adapters to help facilitate the cranking compression test and suggests the following precautions and instructions before testing.

1) Remove the air cleaner and muffler to allow for free flow while spinning engine over.

2) Remove the fuel nozzles from all cylinders and install compression tester of at least 600 psi.

3) Pull the fuel stop lever, or override the stop solenoid. Turn the engine over with the starter until the maximum pressure is obtained. Crankshaft rotation must be at least 250 rpm.

4) If the pressure is less than the allowable limit, rotate each piston to top dead center (TDC) and inject 1 ml of clean 10W engine oil in each cylinder and retest.

5) If the readings do not improve, suspect the engine valves of leakage, a bent rod or worn pistons and rings.

6) Compression variance between cylinders should be less than 10 percent.

7) If compression readings are close to the allowable limit specification, the engine may run but it will never develop full horsepower. As much as 25 percent loss of power should be expected.


Engine Builders: This next item concerns a crankshaft caution, this time for Detroit Diesel 8.2L diesel engines. According to the AERA Technical Committee, this information should be considered any time the crankshaft requires replacement.

There were two different crankshafts used in this engine manufactured between 1979-’90. Although journal specifications as well as the casting number (c/n 8922124) are the same, the bolt hole for the flywheel is physically different.

The first crankshaft design (p/n 8920193) had the flywheel mounting bolts located too close to the outside diameter of the seal surface. The second design (p/n 8922124) had the flywheel mounting holes located approximately .2? (.5 mm) closer to the crankshaft centerline.

If the wrong crankshaft is installed, substitution of the appropriate flywheel will allow the use of the installed crankshaft. However, it is an inconvenience and unwanted expense which can be prevented by simply checking the rear of the crankshaft before installation.


Engine Builders: The AERA Technical Committee offers the following information regarding overheating of 1995-2002 Ford 2.5L VIN L engines (used in Contour and Mystique cars) caused by lack of coolant flow.

Many engine overheating problems have been traced back to shattered plastic water pump impellers found in the OE water pumps. Aftermarket water pumps equipped with steel impellers reduce the chance of engine failure due to overheating.


Engine Builders: During the rebuilding process on Navistar 6.9L and 7.3L diesel engines, the block deck may need to be machined. When this is done, the piston protrusion is affected and usually is higher than the OE specification calls for. Standard OE piston protrusion for these engines is shown in the chart below, left.

One way of getting the piston protrusion to be within OE specifications again is to use a piston that has been “topped” .010?. AERA is currently aware of one aftermarket supplier that has pistons with .010? removed from the top of the pistons. Pistons are available in standard as well as .020?, .030? and .040? oversizes.

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