1989 Range Rover Classic
The pistons were re-used from the old motor, but each cylinder was honed to match it's specific piston. I replaced the oil at 500 miles, but didn't check it since the noise hadn't appeared yet. I'll give it a shot and seem what comes up.Piston sap is totally possible but usually goes away after the engine warms up unless the cylinder bore is way out of spec. Brake torqueing would allow you to get a good sound clip and possibly isolate the noise better with the vehicle stationary. If the noise is present it could indicate a possible issue that should be looked into. A freshly rebuilt engine should not exhibit that sort of knocking noise. The next level of investigation would be to pull the oil pan and removing bearing caps and inspecting bearings.
Were your pistons reused when the engine was rebuilt? Did the engine builder hone each cylinder to match a specific piston?
Have you drained the oil to see if there is debris present?
Your other option is to just drive the truck and hope it fails within the warranty.