16100-ZV4-651 Honda SEE PART DETAILS - SUP; CARBURETOR ASSY. (Honda Code 6861959).

Introduction
Do not perform any procedure in this Special Instruction until you have read the information and you understand the information.This Special Instruction provides guidance for occasions when pitting is discovered in the cylinder block bore near the upper liner seal.Usually, pitting in this region is cosmetic in nature, located below the sealing surface, is shallow in depth and poses no functional concerns for the block.Pitting near the upper liner seal can result from localized boiling due to improper coolant chemistry, high altitude operation, low coolant level, incorrect or malfunctioning cooling system components, or a combination of such factors.By understanding what contributes to coolant boiling, and actively managing those contributors, pitting in this region can be prevented.Cylinder blocks with severe pitting can be salvaged if necessary.Reference Section
Special Instruction, SEBD0518, Know Your Cooling System is a well-established and comprehensive guide to proper cooling system chemistry and maintenance.Reuse And Salvage Guidelines, SEBF8255, Procedure to Salvage Cylinder Blocks of 3500 engines is a well-established and comprehensive guide to 3500 cylinder block salvage. It has been recently revised to include guidance for inspecting and salvaging blocks with pitting in the upper bore.Operation and Maintenance Manual, SEBU6250, Caterpillar Machine Fluids RecommendationsPrevention
Illustration 1 g06052390
(A) Piston
(B) Liner
(C) BlockPitting near the upper liner seal can result from localized boiling due to improper coolant chemistry, high altitude operation, low coolant level, incorrect or malfunctioning cooling system components, or a combination of such factors. Actively maintaining your cooling system is the first and best defense against pitting in the cylinder block near the upper liner seal.The boiling temperature of coolant is determined predominantly by two things:1.Amount and Type of Coolant2.System Pressure1.Amount and Type of Coolant
Illustration 2 g02143785
Coolant boiling point concentration chart
As shown in Illustration 2, as glycol concentration increases, so does the coolant boiling point. For optimum performance, Caterpillar recommends a 1:1 mixture of a water/glycol solution for most applications. All Caterpillar diesel engines equipped with air-to-air aftercooling (ATAAC) require a minimum of 30 percent glycol.In 3500 applications where pitting near the upper liner seal has developed, or is at risk of developing, glycol is essential. In these applications, a solution maintained between 50 and 60 percent glycol is required.Note: If system inspections reveal the need to top-off the coolant system, a well-mixed solution of the same type and glycol concentration must be used to maintain the same system performance. Refer to Special Instruction, SEBD0518, Know Your Cooling System and to your engine-specific Operation and Maintenance Manuals for more guidance.2.System Pressure
Illustration 3 g02143780
Pressure/Temperature Chart
Referencing Illustration 3, one can see the direct relationship between cooling system pressure and boiling point. As cooling system pressure goes up, boiling point goes up. Conversely, one can also see that operating altitude is indirectly related to boiling point. As operating altitude goes up, boiling point goes down.Although there is little that can be done to alter the altitude of an operation, some cooling system components and the coolant level require regular attention to ensure that maximum system pressure is maintained and the boiling point is as high as it can be.
Illustration 4 g06052433
Radiator Cap
Illustration 5 g06052436
Thermostat
The maintenance interval section of most Operation and Maintenance Manuals recommends periodic cleaning or replacement of pressure caps, relief valves, and water temperature regulators. Water pumps must be operating correctly to provide sufficient flow and pressure, and water temperature regulators must be the correct part number and be functioning correctly to reduce baseline coolant temperature.It may seem trivial, but a low coolant level can significantly reduce boiling point since a large volume of compressible air above the liquid can lower the overall system pressure.All elements of the system must be in good order and functioning well as a system. Do not underestimate your role in inspecting and maintaining your cooling system for optimal performance.Refer to Special Instruction, SEBD0518, Know Your Cooling System and to your engine-specific Operation and Maintenance Manuals for more guidance.Inspection and Assessment of Pitting Near the Upper Liner Seal
If pitting near the upper liner seal is discovered, two things must be determined to assess options:
Location
SeverityLocation: (From the Block Surface)
Illustration 6 g06046425
Illustration 7 g06046427
(1) Non-Sealing Region
(2) Sealing Region