Harmonic balancer question I can't find the answer to

[JakePSD]

Why does the 4.0L have to have the rubber between the 2 parts that always seems to fail? Given the failure rate, why couldn't a person just weld them together? Is there some magic in that rubber that makes the engine fairy's happy and makes it run? Or is it just some stupid thing an engineer came up with to reduce NVH by .001%? Or is there actually a good reason behind it? Many other engines have solid crank pulleys. Why doesn't this engine?

 

[JakePSD]

Bump bump

 

[Turdle]

If this is leading to "can I weld my balancer?" I would say not. Any material added could cause it to go out of resonance, which could lead to a catastrophe.

It could be the vulcanized rubber joint is to absorb some engine vibration, and might even help with the front main bearing stress caused by the accessory drives load.

The V8 main pulley is also configured this way. I've seen them slip also, which will lead to ignition timing being off by a few degrees.