Office of Steam Forum for Model & Toy Steam Gas & Hot Air Engines

those tiny view ports are near worthless & if you can put a PMR sight glass in there as a replacement I would highly recommend it. a D3 can be a fun engine....with a ton of work. watch for port alignment from the steam chest into the cylinder assembly , mine was off by quite a margin & significantly made the engine an underperformer, a simple drill bit of the proper size slid into both pieces to check for alignment will give you the answer.