if i had an IQ of 141 i guess i would know what type of engine your after building... gas turbine, two stroke, four stroke, steam, wankel

designing and making a two or four stroke is no real big issue in principle, getting it to run for more than five minutes without it self destructing can be a bit rocket science

a manual mill and a lathe would see you through building a two or four stroke (belt driven cam's) and maybe a wankel if you add cnc

give us an idea as to type and use