BASE AS 3243012 - Caterpillar

For a new G3400 Engine, the typical range for crankcase blowby is approximately 22 to 37 L/Bkw-hr (0.6 to 1.0 cu ft/Bhp-hr).Measure the crankcase blowby of new engines. Record the data. Continue to periodically measure the blowby. Comparing the recorded data to the new data provides information about the condition of the engine.Note: Crankcase blowby is one of the three factors that help to determine the major overhaul interval. For more information, see this Operation and Maintenance manual, "Overhaul (Major)" topic (Maintenance Section).After a new engine is used for a short time, the blowby can decrease as the piston rings are seated. The blowby will gradually increase as the following components show wear:
piston rings
cylinder linersNote: A problem with the piston rings causes the oil to deteriorate rapidly. Information regarding the condition of the piston rings can be obtained from the measurement of the blowby and the results of oil analysis.The blowby of a worn engine may exceed the blowby of a new engine by two times or more.A sudden increase in blowby could indicate a broken piston ring. The following conditions are other potential sources of blowby:
Worn valve guides
A turbocharger seal that leaksA rebuilt engine can have a high blowby due to the following factors:
The piston rings are not seated properly.
Worn parts such as valve guides were not replaced.Excessive blowby may indicate the need for an overhaul. By keeping a record of the results, a gradual increase in the amount of the blowby will be noted until the amount has become excessive.To measure the blowby, use the 8T-2700 Blowby/Air Flow Indicator. Refer to Special Instruction, SEHS8712, "Using the 8T-2700 Blowby/Airflow Indicator Group". The instruction is provided with the tool.Keep a record of the results.For more information, see the Service Manual, "Systems Operation/Testing and Adjusting". For assistance, consult your Caterpillar dealer.