24. Knocking sounds in the lower part of the engine

Unfortunately, such a sound is almost always a failed rod bearing. It is sometimes accompanied by a loss of oil pressure, but by no means in every case.

The knocking sound from a rod bearing in early stages of failure will usually change rather profoundly as engine RPM is raised and lowered from idle to just above idle, and in some cases, the knocking sound can be made to disappear completely by RPM changes.

As the failure progresses, however, the sound will get much worse and eventually be very constant. The only cure for failed rod bearings is to remove the engine for a major overhaul. - Updated: November 4, 2003