Try to turn the compressor by hand. It should be possible to turn it around. It should turn around smoothly, without any 'hickups' (be sure to completely shut down the air compressor!). Check the isolation of the motor windings.
[pdf] An EU/EPA approved diesel air compressor is a type of air compressor that is powered by a portable air compressor diesel engine and has been certified to meet the stringent emission standards set by the European Union (EU) and the United States Environmental Protection Agency (EPA).
[pdf] Disassemble the air compressor cylinder head. Refer to Procedure 012-106. Use a coupling puller, Part Number 3376663, or equivalent, to remove the spline coupling hub. Remove the front thrust bearing. Remove the three flange head capscrews. Remove the three captive washer capscrews.
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