Here's why:
* Big end bearing knock indicates significant engine damage: A knocking big end bearing means the connecting rod journal is damaged and there's excessive clearance. This leads to significant oil loss, as the oil is escaping past the damaged bearing instead of lubricating the engine properly.
* Reduced oil pressure: The oil loss from the damaged bearing causes a drop in overall oil pressure within the engine.
* Hydraulic tappet operation relies on oil pressure: The hydraulic tappet adjusters in the CVH engine (and many others) rely on oil pressure to maintain the correct valve clearance. Lower oil pressure means the tappets may not be able to fully compensate for wear or changes in temperature, leading to increased valve clearance.
* Increased valve clearance results in tappet noise: This increased clearance between the tappet and the cam lobe causes the characteristic "tappet" or "tick" noise.
In short, the big end bearing knock is the primary problem, but the low oil pressure it causes is a secondary effect that directly impacts the hydraulic tappets, resulting in increased noise. Addressing the big end bearing failure is crucial; otherwise, further damage to the engine is inevitable. Ignoring the noise and continuing to run the engine will likely lead to catastrophic engine failure.
