Hello, Trevor:
The knock subsides when the engine warms up? Sounds like piston slap. The
B230F uses lightweight alloy pistons that expand slightly at operating
temperature. When the bore starts to show some wear the result is a less
than perfect fit when the piston is cold, and so the pistons rock in the
bores as they travel through their intake and compression strokes. Pistons
expand as the engine warms up, and it's gone.
Only way to correct this is to pull the motor, rebore the block, and install
oversized pistons. However, it's really more of an annoyance than an actual
problem. The motor will probably run like this for another couple hundred
thousand miles with no ill effects.
