I just put a new fixie together and after a few weeks of riding I noticed some play in the bottom bracket (it is a cartridge bearing bottom bracket). I tightened up the adjustable cup (left side) and it feels fine but I get the feeling it is a problem which will come on again gradually. One thing I noticed is that there is no lockring on the adjustable bb cup.
Thanks

As has been noted many times before make sure there is no tension on the chain (able to deflect slightly) at the tightest point. I'm not familiar enough with the use of cartridge bearings on a fixed gear to say if they loosen up more than a BB with a lockring.

Let's see -- you would have to remove a crankarm to tighten the BB cup, and then reinstall it. Any chance that the cranks weren't torqued properly onto the BB?

Did you torque the BB correctly with a torque wrench or did you just guess? They should not come loose if tightened adequately.

I just guessed. I guess my problem is that it was not tightened enough. Is it the type of thing which you tighten as much as you can?

Yes there is a chance. I will take that into consideration when I look at it again.

If you don't have a torque wrench, you should buy one before going further. Damage to the crank can result if it's too loose or too tight. Torque should be 25-32 ft lbs (I shoot for 30): https://www.parktool.com/blog/repair-...s-and-concepts

Back when there were only loose ball bottom brackets and I only had a BB wrench that I could hook up to a torque wrench. The end result was a good effort standing over the bike and pushing down on the wrench. Since I use the same technique with the cartridges and they do not come loose. The only caveat is tightening an Italian BB, which took a full on best effort with a fixed cup wrench.

Ok Will do. Sounds like the safest/smartest option.

Thanks for the terrific advice all