DoubleTap

I've searched and talked to shop mechanics about this issue, and I've yet to find a definitive answer. I'll try to be concise.

The bike is a 2012 Pinarello Rokh with an Italian threaded bottom bracket shell currently using a SRAM Force crankset, and the bottom bracket is an aftermarket GXP bracket installed by my LBS last year. I'm unsure of the BB brand. I have a new Quarq Riken GXP power meter that I bought in December and installed on a different bike (my winter bike). I am now trying to move the Quarq to the Pinarello, and when just beginning to tighten it down, it preloads the bearings well before it's torqued. The crank won't even spin after just hand tightening the Quarq, and I haven't tried to torque it for fear of damaging something. I've taken it to two trusted bike shops and they both think the installed bottom bracket is slightly too long and that I need to replace the bottom bracket. So, I have special ordered a new bottom bracket because the GXP Italian threaded models are hard to find.

But, I'm trying to better understand what's going on here. Are some bottom brackets longer than others? I thought the SRAM compatible GXP BB's were all the same, but visually the cups on the aftermarket BB currently on the Pinarello appear to be slightly wider than those on other bikes I have (effectively making the BB longer). Are there different models of the BB cups? I've checked for spacers, etc. and there are none. It's just the BB installed on the Pinarello, no spacers.

Thanks for any insight you can provide. I think I have the problem solved, but I want to understand what has caused it.