justonwo

I recently replaced my 9100 crankset with an SRM PM9 with Look cranks and Ti 24 mm spindle. This is going into a BSA BB.

After installing the cranks with 9200 chainrings, I noticed lateral runout on the large ring. I thought it might be the chainring so I replaced with another 9200 chainring. Same wobble.

It doesn’t evenly go from high to low, which I would expect if the ring were not perfectly orthogonal to the spindle. It’s more like a “bump” in the chainring. Almost makes me think the four connection points on the spider aren’t in the same plane.

The net runout is about 1 mm or so. It’s relatively minor but also means I can’t get my FD cage as close as I’d like. And these cranks were eye poppingly expensive.

Thanks in advance for the help.

grumpus

I'd check the thickness of the arms by the bolt holes with a vernier gauge - if one is different that would seem to be an obvious manufacturing fault, and cause for a warranty replacement. If it's not that obvious, maybe find someone with a surface table, dial indicator, gauge blocks who can check the whole thing for alignment.

wheelreason

There are two ways to handle this. First check to make sure the issue isn't due to the mating surfaces not sitting properly, or the bolts, if you rule that out, if it's a symmetrical bolt pattern, you can spin the ring around (to a different arm) to identify if the discrepancy is in the ring, the arm (or both). I just break out the Campy mallet though...