Just purchased a used dirt bike for my son and he rode it last weekend and all was good. Then he noticed a vibration in engine (you can feel it when your gripping the throttle) but doesn´t do it when it is in gear...took it to extreme powersports to have them look at it. Said it could be the crank bearing and would cost me over 350 to have it fixed...I have been doing a lot of research and there are so many things it could be. Any help or suggestions would be greatly appreciated. I think they are just wanting the work and im going to get screwed...I´m going to pick it up tomorrow and bring it home without letting them change the bearing in it...How do i go about trouble shooting a problem like this. PS...i am going to school to become a motorcycle mechanic but just started so my knowledge is limited. However, i can mechanic on my truck and diesel engines with no problem....NOw dirtbikes will open up a whole new adventure for me...Thanks for your help and suggestions. I also have a 2001 Honda CR250R that my son ran in a sink hole filled with water and mud and ended up siezing the engine. They want ove 1600.00 to fix it (the main reason I am going to school..i plan on fixing this myself) any suggestions as to if there is rust what part of engine or should I just buy a new engine and install it????? thanks...hoping to hear from someone out there