They MUST have screwed up when they replaced the head gasket. I would get on the shop that replaced the headgasket about this.

This engine will not break a chain when cared for. It has a double row chain with a short run and no complicated turns and bends. With proper oil changes there is no reason the chain won't last a min of 200k-250k miles. And even then, it won't break without giving ample stretch warning.

Each engine has its own minor faults. The M104 with the headgasket leak and the M112 with the harmonic balancer issues. You have a bullet-proof engine, trust me.

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Ali Al-Chalabi

2001 CLK55
1999 Dodge Ram 2500 Cummins Diesel
2002 Harley-Davidson Fatboy
Merlin Extralight w/ Campy Record