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Drive pin hole slightly large
I have an american bottom bracket and a one piece crank. The drive pin and drive pin hole are not exactly the right size for each other so the crank has a little bit of play to it. Normally this isn't a big deal but this is on a fixed gear. When switching from pedaling forward to resisting motion you can feel the pedal slip just the slightest bit as the drive pin moves about 1 or 2 mm. Any ideas on how to stop this? Would a spot weld be good or should I come up with something a little less drastic?
Not sure a spot weld would work, as your cranks are likely steel and the chainring is probably aluminum. Sounds like that chainring may be meant for 3-pc cranks? I'd recommend finding a BMX style chainring that fits snug.
No other ideas? I ordered the parts together from a bike shop so I figured they would give me properly fitting parts. Hmm.
I would send a note to the bike shop explaining the problem and see if they have any suggestions.
I think this is actually not that uncommon. One piece cranks aren't typically used on fixed gears so the pin would normally only get pushed one direction.

I think you'd be able to force some metal into the gap to take out the play. Ideally you bend something over the end of the pin so when you tighten the chainring down it just fills the gap. Note that you need to be carefull not to put something too thick so that it forces the chainring out and bends it. Needs to be just the right size. Of course, check with the seller first to see if it was a defect or just a crank with low tolerances.

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