Must be the luck of the draw. I have had my SAP180 on a Funtana 125 for a year now. Many flights, 5 gallons of fuel through the engine. No problems with prop coming loose or the muffler bolts coming loose. It came with the Nord Locks installed at the factory and have never been taken loose. Did you remove the muffler after getting the engine or did they just come loose? I do have the engine mounted on a very strong 1/4" thick marine plywood face plate, bolted and glued to the engine box. I needed that 1/4" to get the engine/cowl lined up to my satisfaction. It also helped with balance since I have 3 servos in the tail.