Are all square taper bb spindles the same tapers?

[Decan]

Thanks all, especially weeman_mtb and 02gf74 !
To be honest, the issue isn't that of buying something which turns out to be a pup. My real concern here is that these crank arms appear to be absolute minters to me and I just cannot understand why they are not reasonably snug on a JIC bottom bracket spindle. Can't stand to throw them out when I feel that there is something missing.
These arms are mint from top to bottom. Not even damaged at the pedal ends. Tapered BB holes look perfect to me. I can see the marks of the BB being pressed against the insides of the crank holes - towards the centre alone.
Just don't get it !!
Could the previous owner have has them on a BB spindle which was marginally wider?
Will replace these but refuse to dump them without understanding the issue !
They're perfect apart from this unexplained deficiency.
Is it possible that UN 71 or UN 72 BBs of that time were ever so slightly wider ?

Really appreciate your views !! Thanks..

 

[FluffyChicken]

Re:

The tapers are not mint though, the sides are further out than the corners

 

[legrandefromage]

Is it possible that UN 71 or UN 72 BBs of that time were ever so slightly wider ?

no.

 

[mattr]

My gut feel is aluminium wont do it, better try using steel from baked bean cans, would be thicker, possibly steel from a sardine can lid be thinner, lots of epoxy to hold in plaice.

aluminum is perfect as it conforms to all the lumps and bumps on both axle and crank, giving a better joint. Grease is only there to hold the metal in place while you tighten, epoxy will be massively overkill, and won't squeeze out as readily, if at all.

Steel square taper cranks used to be a nightmare for coming loose for exactly the same reason, unless you swung on the bolts and used twice the recommended torque. Probably why no one makes them anymore. And TBH I've only ever seen a couple, and those i used to see regularly. For tightening, again.

 

[02gf74]

Past exp has shown me that al (noit some fancy alloy) is to soft and defkrms far toi easily but no harm in giving it a go.

I used epoxy plus a bit of extra torque to hold a LH crank that came loose on the way up to Mt Teide.

Some measurements
UN52. 17.2 (14.1) 12.8 14.0
UN72. 16.8 (11.4) 12.8 13.9

Length of taper (mark showing how far crank got to) taper at end. taper at fat end

 

[02gf74]

BTW my hands were frozen from holding the cold metal bb to measure them which didnt take long.

.... and it is snowing albeit not heavy.

 

[Decan]

Thanks for those..
A few more measurements, with one extra dimension

1989 shimano cup and cone spindle
Well used bb un54 spindle

Dimensions
length of taper to full diameter point,
length of taper to point where it tapers up sharply,
Mark showing how far previous crank got to
taper at thin end,
taper at fat end

17.5, 15.6, 14.3, 12.75, 13.7
17.3, 15.3, 14.9, 12.8, 13.6

Dimension of the inner (larger) taper of the crank arms - 13.9 mm !

The dimensions of the outer tapers of the crank arms which don't tell us much are - left 11.9, right 12.1.

Not sure where this leaves it :shock:

Hope you've got some blood back into those hands ha ha - do appreciate it though, thanks!

 

[weeman_mtb]

Re:

Here's a photo of an M737 drive side crank of mine that is definitely a good 'un, sorry I couldn't persuade our rubbish camera to focus properly.

Think FluffyChicken is right, the sides of your squares bulge out past the corners on closer inspection.

 

[FluffyChicken]

Re:

there will be a bit of bulging if it was clamped tight against the end stop. I wonder if someone has placed it on an ISO or shorter JIS axle (iir Syncros are a bit shorter than noraml) and clamped it down far to hard over time.

Either way I'd just look for some more arms :-(
Or see if the newer shimano bottom brackets with the chainline stops clamp it down when you hit the stop (like ISIS do).

 

[02gf74]

Hmmm your measurements match mine quite closely, got to br the crank then.

The fact the hole on the inner side is 0.2 mm than the spindle says they're knackered.. send them back for refund.

BTW the inner square hole in a Sugino c/set i have lying round measures.
13.3 mm rh
13.54 mm lh