attaching toothed wheel to crank pulley

Would just welding one on cause balancing issues ?

Thats what mine has been done like Rob, all i know is they sent it away but im not sure if it was to be welded properly or balanced.

yes it will need balancing. As should anything that is changed to the rotating assembly.

You could get one of those Lupo toothed wheel sensors. They mount behind the flywheel. No balancing issues, and no scavenging of power...

Like this.....

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JNLRacing wrote:yes it will need balancing. As should anything that is changed to the rotating assembly.

would it just be the pulley itself that would need balencing rather than the whole crank assembly?

the lupo is another option in the back of my mind.
probably the cleanest..

I don't think that welding a toothed trigger wheel to the crank pulley will cause any balancing issues as long as it's done well. i.e. the welds are symmetric and the wheel is mounted perpendicular to the crank pulley axis.
There's also so little mass in a trigger wheel and it needs to be concentric to the crankshaft axis to give a reliable signal to the VR sensor that I can't see it creating any significant source of vibration.

In order to balance the pulley you need to balance it to a crank but if you are going for a zero balance on a two up two down 4 pot it doesn't have to be balanced to yours in particular any crank that is on the shelf already balanced will suffice.

^^^^ @andydavy yes in a realistic world that is the case, but remember that vag front pulleys are harmonic dampener which means they are more sensitive to weight changes.