What do balance shafts do?

[1gE.T.]

What are balance shafts for? I saw this project talon on prostreet.com and this guy removed the balance shafts. I looked in the repair book and it doesnt say what they are for. Someone please fill me in.

Thanks

 

[NOSNUSE]

they cancel out vibrations from the motor. they are just shafts with counter weights offset on them.

 

[RabidDonkeyBoy]

4cly engines aren't balanced when they rotate, so they generally use weighted shafts that spin @ 2X engine speed to cancel out any vibrations.