Q: 2001 Chevy Blazer distributor install.. it is at top dead center and the rotor lines up with the 6 but is not seated all the way.

If you are using the marks on the harmonic balancer to find TDC, occasionally the balancer will have shifted (the rubber bond breaks) causing the timing mark to be some degrees off. Consequently, the crankshaft is not really at TDC and, of course, the camshaft is not in the position you think it is. The result is the distributor gear won’t engage. If that is not the cause, examine both gears and simply attempt to re-position the distributor but if it does slide in but you can’t get the rotor to line up that is a sure sign that the markings on the balancer have shifted and the balancer is the problem. To obtain service on this please request timing mark inspection - possible harmonic balancer issue and the responding certified mechanic will get this taken care of for you. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.