Does anyone know why GM went to the trouble of making the spacing of the holes on the Harmonic Balancer, and it's mating hub NOT 120 degrees?

I ask because the under drive pulley that I have recently tried to install had holes evenly spaced at 120 degrees, making the installation impossible.

I searched other threads for this information, attach link if this has already been discussed.

 

Since the hub and pulley are two pieces, they likely did it so they could only be mated one way. This maintains phasing of the timing pointers and any balancing that might have been done at the factory. Not sure how knowing why they did it is going to help.

 

Yeah,

The question of why was asked to satisfy my curiosity.

Are all LT1's Like this? I know that some balancers/Pulley require a 3-jaw puller, while some have threads to use a harmonic balancer puller.

I had ordered a pulley that was evenly spaced out at 120 degrees, of course it did not fit.

 

As far as I know, all the harmonic dampers are the same, with the "offset" mounting holes. Both the damper and the hub have TDC markings.

The puller "technically" isn't required.... its just the rust that builds up over the years that make it necessary. Its actually a "loose fit" when new... I changed mine out for an ASP damper/UD pulley when the car was only a couple months old, and the damper literally fell off the hub when I got the three bolts off.

 

There is an early and late model style of pulley like you describe.