Its proper title is a harmonic damper and thats one of the worst i have seen. Replace it and you will be surprised what a difference it will make to the van plus it will save some serious damage if it does give way T:T:
Thant my friend is 'FUBAR'
Exactly what mine looked like before i changed it!
Don't forget you need a new crank bolt and diamond washer when changing it as its a stretch bolt.
Also it will be stupidly tight and needs the correct insane 460Nm or 340ft lb torque when re-fitting.
Quite a few folk on here have had them shear off, timing goes out and the cam shaft snaps.
Get it done asap.
I got a virtually new one off eBay for £40