Fa-50
It is so hot here in this part of Texas I decided I needed an inside project since I don’t want to go flying when it’s over 100 outside. I’m building an LT-40. I’ve had a few suggestions of what engine to use. I decided I would start with a FA-50. I have 3 of them and got out the test stand to pick an engine. Two of them ran very well but one was down on power. All of them were tested with my low nitro fuel and I used the Saito black hot dog shaped muffler on all the engines. I used the same 12X6 on all of the engines.
Once back in the shop with the AC running full blast, I decided to open up the engine that seemed down on power. The bearings felt good but looked all gooked up. About an hour later I had the bearings changed with a new set and I changed the seal where the intake goes into the head. Next to give it another run.
The top end was great. This engine spun up better than the other two I tested. I had the low end still set a little rich. Here is where it gets really strange. At any throttle setting under 4000 RPM, it makes a knocking sound.
I opened the engine to look inside. The con rod feels good. There is no slop that I can feel in the bearings. I ran the engine again and it still does it. The knocking sounds had me so puzzled that I called Lonnie and let him hear it over the phone. One thought we talked about was a sticking valve. I pulled the valve covers and the valves move fine but just to be safe I oiled the valve stems with 3 in 1 oil.
Another run and it still does it at any throttle setting under 4K RPM. Anything above 4K and it sounds great. It will idle at 2K forever but it knocks. If I put my hand on the engine, I can feel the knocking.
Has anyone ever had this problem? What do I need to do to get rid of the knocking? This engine didn’t act this way until I changed the bearings.