I have to think of an object to draw in my CAD class and was hoping someone might point me in the direction of the dimensions for a generic car piston or something similar? I know this leaves a lot of scope and may make an answer difficult to come by but any help would be appreciated.
What textbook are you using?
The Giesecke - Technical Drawing book I use has a dimensioned piston.
Does your school have a library with drafting books?
If so, one of them probably has a piston drawing.