SCARIFIER CYLINDER GROUP 8J7321 - Caterpillar

Table 1
Cylinder Head Groups    
   Natural Gas
Low Compression Ratio (9:1)
Part Number    Natural Gas
High Compression Ratio (10.5:1 and 11:1)
Part Number    Low BTU Fuel (1)
Low Compression Ratio (9:1)
Part Number    
Cylinder Head Group (2)     7C-0400     N/A     172-2227    
Basic Cylinder Head Group     171-3994     194-3250     185-3606    
Exhaust Valve Seat Insert
prefinished
20 Degree     171-3993    
Inlet Valve Seat Insert
prefinished
20 Degree     171-3992    
Insert (Prechamber assembly)
Standard Size     148-7142    
Insert (Prechamber assembly)
0.25 mm Oversize     148-7143    
Insert (Prechamber assembly)
0.50 mm Oversize     148-7144    
Exhaust Valve
20 Degree     154-2417     185-1103    
Inlet Valve
20 Degree     4P-2854    
Valve Stem Seal     N/A     N/A     153-7002    
Rotator Assembly     189-4583    
Inlet and Exhaust
Valve Guide
Standard size     175-6344    
Inlet and Exhaust
Valve Guide
0.5 mm Oversize     183-5074    
Inlet and Exhaust
Valve Guide
1.0 mm Oversize     183-5073    
( 1 ) This includes applications that use landfill gas or Bio-gas.
( 2 ) These cylinder head groups are not available for parts service at this level.Serviceability
Except for the valve seat inserts, the new cylinder heads can be serviced and rebuilt with the existing guidelines. The new 171-3992 Valve Seat Insert (Inlet) and the new 171-3993 Valve Seat Insert (Exhaust) can be installed without any special operations for finishing the valve seat in the new cylinder heads. These valve seat inserts are premachined to the proper specifications for the valve face angle. The machining process has been improved for the following parts: the cylinder head, the valve seat inserts and valve guides. This allows these components to be assembled together without any further machining.The new cylinder head groups will meet the service intervals that are identified in the guidelines for maintenance.Note: The 171-3992 Valve Seat Insert (Inlet) and the new 171-3993 Valve Seat Insert (Exhaust) can not be used with the earlier cylinder head casting.The 187-6273 Prechamber Machining Tool Group can be used if the seat in the cylinder head for the prechamber assembly requires attention. Refer to Tool and Operating Manual, NEHS0790, "Using The 187-6273 Prechamber Machining Tool Group".