Ashtabula crank, fixed gear
I'm building a fixed gear on a bike with a one piece crank, and I have an aluminum chainring on a bmx spider like this one:
However, the hole for the pin on the spider is larger than the pin on the crank causing the pin to move back and forth in the hole when pedaling backwards and forwards. Is there some simple fix for this or do I need to upgrade the bottom bracket to support a standard crankset? If so, can you help me pick the offset that will preserve the straight chainline I have now?