Cylinder Block And Cylinder Liner Pitting Caterpillar

Problem:

Reference: Engine News, November 1998, Page 23, "New Field Service Piston Assemblies And New Production Piston Assemblies"

Gas Engine Customer Service has observed pitting problems in the cylinder liner and block on G3600 engines. Several sites have reported liner pitting that has been 5 to 11 mm deep after approximately 5,000 hours of engine operation. Block pitting was also observed in many of these cases. The pitting has been primarily observed on high compression ratio (11:1 and 10.5:1 compression ratio) G3612 and G3616 engines, and it is always on the thrust side of the piston. The thrust side is on the outboard side of the liner on the odd bank, and it is on the inboard side of the even bank. Pitting has been more predominate on the odd bank.

Solution:

The magnitude of the problem is undefined. Data would tend to indicate that the skirt profile, introduced with the piston changes outlined in the REFERENCE Engine News Article, is the prime suspect. The looser skirt profile would cause the piston slap to increase, which will remove the coolant protection on the liner. However, there have been several sites that have reported pitting with the older piston skirt design. In these instances, other contributors have been identified as root causes. These include operating pressure on the jacket water system and coolant quality.

Based on expereince, engine operating hours are an important guideline that should be tracked on all 10.5:1 compression ratio engines that are operating with the new piston skirt design (part numbers 157-1111, 152-3826, and 156-5753). The new skirt design was implemented with the following serial numbers: G3612 (1YG00137) and G3616 (4CG99). However, many engines have been updated with the 10.5:1 pistons to combat detonation concerns, and they must be included on the watch list. Engines with the new 10.5:1 pistons that have accumulated more than 5,000 hours need to become focus sites, and additional data on jacket water system operating pressure, and coolant quality needs to be obtained as soon as possible.

The pertinent jacket water cooling system data includes:

* Jacket water system operating pressures

* Pump inlet pressure should not be less than 35 kPa (5 psi)

* Pump outlet pressure should be greater than 250 kPa (36 psi)

SOS analysis of coolant used in jacket water system:

* pH level should be between 8.0 and 11.0

* Glycolate should be less than 400 ppm

* Nitrite should be greater than 1500 ppm

Any engine not meeting these guidelines is likely to aggravate liner and block pitting problems, and corrective action must be implemented immediately. The steps that should be taken include:

* Investigating the root cause for low coolant operating pressure (faulty expansion tank pressure caps have been found in several cases)

* Insuring that proper maintenance and monitoring of the cooling system is occurring

Work is proceeding on the investigation of the piston skirt profile, operating pressures, coolant type, and additional field data is being pursued.

The liner and block pitting problem has yet to be observed in 9:1 compression ratio applications. This may be due to the lower cylinder pressure and/or operating speed. However, the same cooling system criteria should be followed for these engines to avoid problems. The 9:1 compression ratio piston part numbers are: 157-0726 and 156-1699, and they were in effect with serial numbers G3606 (3XF163), G3608 (4WF83), G3612 (1YG122), and G3616 (4CG82).

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