If it is like the 665, it is a rotary Mico Bosch made in India with Bosch design.
I don't know if the 555 is similar to the 665, but this is what happened to ours. The bolts holding the pump became loose, letting the pump rotate and get out of time. The pump started rattling, sounding like it was going to fly apart. I was sure something had happened to the pump inside.
Before removal, we put the flywheel timing mark on the TDC mark. The pump has a locking screw on the shaft of the pump where you can tighten the shaft preventing it from turning once removed. Carried the pump to the pump shop where they bench mounted and checked it over. Found no defect in the pump. Expensive just to get it bench tested. Said it probably was just out of time.
The shop set the pump back to TDC and locked it down. Once the pump was reinstalled, engine started right up, but you could tell the timing was slightly off. With some trial and error, the correct timing was achieved. (You can tell if the timing is off by the way the engine runs). Rotate it until the engine is very sluggish, then start advancing until it is just right. Some trial and error. On the 665 there is a cover on the front of the engine covering the slotted gear that drives the pump. We just left the cover off until we got the engine timed. Slung a little oil but not much. Hope this helps you some with your problem.