Learned a lot regarding harmonic balancers for our cars. Went to the local GM dealer, they asking price for the balancer was around $268.00 and with my discount, the asking price was around $192.00.
I noticed the GM box said it was made in India just like the balancer sold by ATP, which I paid $108.00 at Rock Auto. Prior to purchase, I opened the box and it was packed identical to the balancer from ATP and the casting numbers were the same as the ATP harmonic balancer. Also, the key way slots are identical in both the GM and ATP harmonic balancers; they do not go the full length like the OEM piece. Since the GM replacement part was identical to the ATP unit, I kept the ATP unit and called the Tech line at ATP.
The ATP guy was very knowledgeable and let me know they buy the harmonic balancer from the same company that supplies GM. I explained the situation with the key slot and he said they have not received any complaints to this date. He also said if I had used the new key supplied with the balancer. I looked and found the new key stuck in the bottom of the box. I removed the old key and noticed the new key is a bit shorter than the OEM. I replaced the key with the new key; slipped the balancer and the car started.
Just like willwren said, the balancer was not deep enough for the interrupter ring to reach the crankshaft sensor.
I called the tech person and ATP and thank him for his assistance. He asked me to send him the old OEM balancer so he can talk to the engineering department and asked them of the possibility of making the slot the same as the OEM balancer. he also said they carry the whole line of harmonic balancers for the 3.8 engines and they are the same identical unit that you get from the GM delarship, except you pay much less. ATO does not sell direct, however you can get them from Rock Auto. www.rockauto.com