Getting to BDC

#1 Remove Glow plug

#2 Get into a light so you can see the top of the piston through the hole you took the glow plug out

#3 Get a hold on the fly wheel so you can turn over the engine

#4 While turning the flywheel observe the piston going up and down

#5 When the piston is at the lowest spot it is at BDC

Hope that helps..............good luck and HAPPYRC'en