My bottom bracket is making a hell of a racket...

[rogerzilla]

I think I explained the overtightening issue upthread but here it is again. If the central sleeve is in any way compressible, tightening puts an axial shear force across the bearing units, which they are not designed to cope with at all. Really bad designs like the Genetic Karyotype will bind unless the LH cup is left very loose (use lots of threadlock). Slightly better ones will just wear out quicker. Good ones have an essentially incompressible metal sleeve which, of course, is heavier. The UN55 avoided this problem completely.

 

[iluvmybike]

not being funny but I never realised that pressfit couldn't be sorted at home - they are a mystery to me. And the word "press" makes everything sound so simple.

Of course they can be done at home - just need the right tools to suit your particular type

 

[Ajax Bay]

If the central sleeve is in any way compressible,

The UN-300 has a metal central section (containing the two bearings) and the left hand end-piece slides over that central section. Nearly all other cartridge square taper BBs are effectively the same. There is no mechanism (I can see) which could achieve compression, unless, I suppose the BB shell was significantly less than 68.0mm, which is an uncommon occurrence (anecdata). Where do you find these niche BBs which, apparently, are "badly designed"? Now I appreciate I'm showing my ignorance (or you are testing my google fu again). How about a link to Genetic Karyotype BB deja vu failure reports (I have looked)?

 

[rogerzilla]

Where did I say a Karyotype had failed? I fitted one, realised that achieving adequate cup tightness caused the sleeve to compress and the bearings to bind, and binned it.