[JFP in PA]

When the pin is through the crank pulley and in the TDC boss, it can have a substantial load on it, especially during an IMS retrofit. Because some under drive pulley's require you to cut a lot of material away, the ability of the remaining material to hold the engine at TDC can become tenuous. Some pulley's can actually block the TDC hole entirely, which also makes an IMS retrofit impossible.

With many of these units, to problem isn't the pulley, it is the amount of the pin boss you need to remove.