BOLT 1739683 - Caterpillar

Engine: 3412 (S/N: 60M1-UP) 3412C (S/N: 60M1-UP; RLR1-UP; 9BR1-UP)Industrial Engine: 3412D (S/N: REA1-UP)Introduction
The problem that is identified below does not have a known permanent solution. Until a permanent solution is known, use the solution that is identified below.Problem
Reports have been received that the 7W-0128 Fuel Injection Lines Gp has shown a high failure rate in specific customer applications. The following double wall fuel line part numbers are included in the lines group:
Table 1
Fuel lines in 7W-0128 Fuel Injection Lines Gp    
1W-6451    
1W-6453    
1W-6455    
1W-6457    
1W-6459    
1W-6461    
1W-6452    
1W-6454    
1W-6456    
1W-6458    
1W-6460    
1W-6462    Two failure modes have been identified:
First Failure Mode The nuts on the fuel lines loosen during engine operation causing a sealing loss between the fuel line and the 1W-6777 Injection Line Adapter .
Second Failure Mode The inner line is experiencing cavitation and erosion that leads to a pinhole leak.Solution
Safety Section
Fuel leaked or spilled onto hot surfaces or electrical components can cause a fire. To help prevent possible injury, turn the start switch off when changing fuel filters or water separator elements. Clean up fuel spills immediately.
Use a suitable container to catch any fuel that might spill. Clean up any spilled fuel immediately.
Do not allow dirt to enter the fuel system. Thoroughly clean the area around a fuel system component that will be disconnected. Fit a suitable cover over disconnected fuel system component.
First Solution
Illustration 1 g03020696
(1) Apply Loctite to treads
Illustration 2 g03020716
(2 ) Witness mark
If a fuel leak is indicated due to loose fuel line nuts, loosen the large and small nut on the affected fuel line.
Clean the threads
Apply Loctite® 242® Threadlocker #24221 to the threads (1) on the 1W-6777 Injection Line Adapter and on the small nut threads.
Torque the nuts to 40 7 N m (30 5 lb ft) starting with the large nut first then tightening the small nut.
Perform an operational and leak check of the fuel lines.
If no leak is present, apply witness marks (2) across the entire joint from the 1W-6777 Injection Line Adapter , including both fuel line nuts, and the fuel line. The witness mark will help to identify a future potential leak from the nuts loosening. If a fuel leak persists, proceed to ""Second Solution"". Refer to Illustrations 1 and 2.Second Solution
Replace the leaking fuel line per Disassembly and Assembly, SENR1133, "Fuel Injection Lines". Use Loctite and witness marks as indicated above