During a training sequence, the pilot in command simulated a failure of the left engine. The pilot under check correctly identified the failed engine, and applied full right rudder to counter the effects of yaw. The flight then continued normally, but the crew were later unable to obtain a down and locked indication for the landing gear. An inspection from another aircraft revealed that the gear was only partly extended, with the nosewheel turned to the right. After all efforts to lower the gear were unsuccessful, a safe wheels-up landing was made. It was later discovered that there was a rigging fault in the nosewheel steering and rudder system. This had allowed a roller, which normally engages in a channel to centre the nosegear during retractions, to move outside the channel when full right rudder was applied. This had resulted in jamming of the nosegear.