811693 Mercury BOWL, Fuel (WME-20A&B/21A&B)

Introduction
This Special Instruction describes the misconceptions of high blowby and oil consumption issues caused by the alignment of piston ring gaps.Do not perform any procedure in this publication or order any parts until you understand the information that is contained in this publication.Understanding High Blowby and Oil Consumption
There are occasional reports of engines with high blowby and high oil consumption that claim to be caused by alignment of piston ring gaps. The aligned piston ring gaps are not necessarily the cause of these engine issues. Caterpillar provides documentation related to high blowby and oil consumption.Refer to your applications System Operation/Testing and Adjusting, Troubleshooting, and Operation and Maintenance Manual as well as the articles listed below:
Special Instruction, REHS7857-00, "Testing for Excessive Cylinder Blowby in 3500 Engines"
Engine News, SEBD9514, "Piston and Ring Wear"
Engine News, SEBD9263, "The Causes Of Worn And Broken Piston Rings"Caterpillar recommends piston rings to be oriented at 120 degrees apart when installing new rings Piston rings are designed to rotate freely during engine operation. The rate of ring rotation is unique for each ring and the rotation will provide a uniform ring and piston groove wear. The ring end gaps will align with one another at random intervals during engine operation. Normal ring gap alignment is brief because the rings continue to rotate at different speeds and directions.The ring end gap dimension will increase over the service life of the engine. Rings exert pressure onto the cylinder wall, and the pressure is a direct function of the rings radial thickness. As the ring face wears, the pressure keeps the ring face in contact with the cylinder bore. This wear results in the ring gap dimension increasing with continued operation.Rate of oil consumption is called Brake Specific Oil Consumption (BSOC). The unit of measure is grams per kw/h or lbs/bhp h. The BSOC depends on the engine model, aspiration, and the operating load and oil that is used. Consult your Cat dealer for assistance in determining the correct oil consumption rate for your engine.Reference: For information on calculating the BSOC, refer to the Electronic Media Center for Engine Data Sheet 96.2, LEKQ4028, "Oil Consumption Data". This Engine Data Sheet can be found at the address below.https://catpublications.com/
Excessive low engine speed or running the engine with a low load for extended periods can lead to excessive oil consumption and carbon buildup on the top of the piston, piston rings and the piston ring grooves. These issues can lead to excessive wear and damage to components.If necessary, gather data using the Service Form, 01-081227-02, "Oil Consumption Test Report", to verify that oil consumption exceeds specifications per amount of fuel burned.Recommendations
In order to minimize risks of blowby and/or excessive oil consumption, follow the maintenance interval schedule for inspection of the cylinders, along with required engine overhauls. During scheduled maintenance inspections of cylinders, insure that rings are free to rotate. Examine the rings for wear and increase in ring gap.Follow Systems Operation/Testing and Adjusting and Troubleshooting for diagnosing engine performance issues. If the piston rings are free to rotate, the location of the ring gap is not likely the cause of high blowby or oil consumption.