I went ahead and swapped out the torx head fastener for the original hex head bolt. I was putting the belt back on after a lengthy repair, and it became apparent that I would need three hands - one to lever the breaker bar, one to manipulate the belt, and one to keep the T50 torx bit engaged with the fastener - it just tends to cam out of the torx head. I don't know if it's the fastener or the bit I'm using - I used a Lisle brand bit, maybe a different manufacturer would fit tighter. But I don't have to search for long to find out that I'm not alone.
Both fasteners are 10x1.5 LH, but the pulley design has changed. The new pulley has a standard bearing molded into it, I'm guessing a cost reduction over the old pulley w/offset flange. The original hex head fastener doesn't allow for as much thread engagement, but it appears to be adequate. The new tensioner has a raised portion that registers the pulley, which precludes use of the original style pulley with the offset flange. And although the original style pulley is still available, as it's used as the idler, I haven't been able to find the new style pulley anywhere online. It appears that the entire tensioner will need to be replaced when the pulley starts making noise.
By the way, the torx fastener is a "trilobular" design - it has three lobes that actually form the thread as they turn. I needed a large impact wrench to remove it, and when it came out, there was a fair amount of galling involved, as INA didn't use any lubricant on the threads. The original fastener threaded right in, despite the messy female threads.
In the picture below, you can see how the original fastener's flange head rests on the inner race of the new pulley's bearing. |