Play in crank arm

[Pauluk]

I inspected my son's mountain bike today and found a tiny bit of play in the drive side crank arm when the arm is in the horizontal position. I can't detect any problem in any other position and the play is very small (you can't see it but you can just about feel it).

I think the BB may be a cartridge type as there is no lock ring as on one of my other MTBs.

My question is, should I try to tighten the BB or should the BB be replaced right away (I'm assuming its the BB as the crank arm seems very secure and tight) or given that the play is very very small can it be left for a bit longer. Can it cause any other damage other than further deterioration of the BB.

Thanks for any advice.

 

[mrandmrspoves]

If it's a cartridge you can delay as the whole cartridge is replaced. Just be totally sure it isn't the crank coming loose..