Originally Posted by
Sport_Pilot
Lapped engines are more prone to compression loss when overheated than ABC engines. In fact that is why ABC engines were invented,. Many a time I have had a Fox Stunt engine barely running because it was running lean and hot, but still running. They are ususually OK after that but not good for the engine,.
I guess I haven't ran one hot enough then... Wait, I thought brass expands more than iron or steel does....
Usually when you get 'em hot is when the castor is supposed to turn into the mystical varnish that everyone speaks of when lapped iron engines come up in conversation.