Parts/Step not fitting ( technic / gear not aligning) working on Lego Technic; Recovery truck.
Reached Step 27(book 1)....fixing the rope spool. and found that the white gear wheel is not fitting in. i.e., i have the white gear fixed on the shaft with the spool, but when i try to fit it on the frame, it does not fit in, if i force it in, it goes on a angle. 
have relooked at the previous steps and can't see any part missed out or put in wrongly. 

Any ideas what i am doing wrong?
isn't the white gear wheel supposed to align with the small black gear wheel?
Problem solved. I had a part wrongly fitted. 
both parts look similar ( black gear wheel)...one(part#6012451) is smaller that other(part #4177431).
back on track now. .. :-)