Rivets/spacers on cassettes (was a misguided question about parallel drop-outs)

[Paul]

I seem to have bent another rear axle. Is it due to:

a. my mighty girth, or;

b. the fact that I have splayed the rear stays to accept a larger-than-they-were-made-for hub, without adjusting the dropouts, or;

c. Brexit?

[vorsprung]

IMHO as long as the wheel is in straight ( no lateral wobble ) shouldn't make any difference

I've never bent an axle, maybe it's you

[Tim Hall]

Freehub or freewheel axle?

[LittleWheelsandBig]

If the dropouts are a long way out of parallel, yes, it often bends axles. A little way out, not so much.

If we are talking about a strong, well-supported freehub with flimsy dropouts that are pretty close to parallel = probably not worth getting the dropouts spot on.

If we are talking about a 7sp or 8sp freewheel in a stiff frame with dropouts a long way out = get those dropouts exactly right for OLD and parallel.

[Paul]

Freehub or freewheel axle?

Freehub

[Paul]

If the dropouts are a long way out of parallel, yes, it often bends axles. A little way out, not so much.

If we are talking about a strong, well-supported freehub with flimsy dropouts that are pretty close to parallel = probably not worth getting the dropouts spot on.

If we are talking about a 7sp or 8sp freewheel in a stiff frame with dropouts a long way out = get those dropouts exactly right for OLD and parallel.

I'm not sure how far out they are. I think they were designed for a 120mm oln hub. The one in there now is 130mm.

It's a 7sp shimano sora freewheel hub.

[LittleWheelsandBig]

If it is a steel frame, just cold-set it and realign the dropouts. It is a ten minute job, including putting the kettle on.

[Tim Hall]

Freehub

It's a 7sp shimano sora freewheel hub.

These two statements do not match. However a swift google suggests it is a freehub, which is good. Freewheels tend to have their bearings inboard of the gear cluster, leading to a longer unsupported length of axle between the bearing and the dropout, which is more susceptible to bending.  However in your case, this isn't an issue.

[Paul]

Freehub

It's a 7sp shimano sora freewheel hub.

These two statements do not match. However a swift google suggests it is a freehub, which is good. Freewheels tend to have their bearings inboard of the gear cluster, leading to a longer unsupported length of axle between the bearing and the dropout, which is more susceptible to bending.  However in your case, this isn't an issue.

  Yes - it is a freehub.

I haven't actually removed the axle yet to be completely sure, but when turning the sprockets are deviating visibly by a mm or more, so something's up. And the 'outness' of the dropouts is visible, so it's my first guess.

[LittleWheelsandBig]

Movement of the sprockets (as you describe) has nothing to do with a bent axle.

[Paul]

 

What might it be?

[LittleWheelsandBig]

It depends.

If you are holding the axle still and turning the wheel and the cassette cogs seem to wobble from side to side, some of that movement is intentional, because of the shaping of the teeth. The same thing can be apparent when holding the wheel still but rotating the cassette.

If the freehub bearings are loose/ worn or the cassette lockring or freehub bolt is loose, then the cogs can wobble from side to side when the wheel isn't turning.

If you are holding the wheel still and rotating the axle and the cassette cogs wave from side to side, that might be a bent axle but that is unlikely.

[Paul]

It depends.

If you are holding the axle still and turning the wheel and the cassette cogs seem to wobble from side to side, some of that movement is intentional, because of the shaping of the teeth. The same thing can be apparent when holding the wheel still but rotating the cassette.

If the freehub bearings are loose/ worn or the cassette lockring or freehub bolt is loose, then the cogs can wobble from side to side when the wheel isn't turning.

If you are holding the wheel still and rotating the axle and the cassette cogs wave from side to side, that might be a bent axle but that is unlikely.

It's not the teeth. The sprockets definitely deviate - by a mm or two - when the bike is on a stand, turning the cranks backwards while the wheel is still.

Freehub bearings are good, lockring tight. I didn't check the freehub bolt but having just replaced the cassette I think I would have noticed if that was loose. I'll take the QR out and have a look down the inside.

[LittleWheelsandBig]

From that description, it is definitely not a bent axle.

https://youtu.be/A6TpHgbbEGM might give you some ideas.

Have a look at a 'known good' cassette/ wheel and see how much the teeth appear to move side to side when spinning.

[Paul]

The case is solved!

Can anyone guess what was causing the sprockets to deviate from true on each rotation, when the axle is straight?

Clue: the problem is with the new cassette.

[Tim Hall]

Bit of crud under one edge of the cassette where it sits on the freehub?

[LittleWheelsandBig]

Smallest cog not correctly orientated?

[Paul]

Bit of crud under one edge of the cassette where it sits on the freehub?

You're really, really close. But the problem seems to be deliberately caused.

(I've just emailed SJSC to discuss).

[Paul]

Smallest cog not correctly orientated?

Nope.

[Paul]

Give in? I'd be surprised if anyone got it.

[rogerzilla]

Wrong spacer combination?

[Paul]

Nope.

It's because - instead of the usual 3 rivets (sometimes screws) holding the sprockets together - there are only two.

The rivets are 120 degrees apart and they protrude slightly at the back, so that they make contact with the spacer on my cassette. Because the rivets are 120 degrees apart, and there is a corresponding 240 degree area without a rivet, the cassette does not sit flush to the spacer, causing it to be slightly out of true on the freehub, which is causing the sprockets to oscillate.

It might not be a problem if I didn't need a spacer, but I do. I might be able to work around it (file the spacer a little, or file down the rivet ends).

But it's a novel one to me.

It's probably a Brexit thing, so if you said 'c', have a 

[Feanor]

Hmm...

All the 1.85mm spacers (for putting 8/9/10 spd cassettes onto 11 spd freehubs) which I've seen have 3 cutouts on them to accommodate the rivet heads, where present.
These rivet heads are not part of the designed spacing, and the cassette should not be bottoming out on them.
The make-up point is the flat machined surface at the back of the cassette.
It is *this* surface, not the rivet-heads, that should be mating up against either the spacer or the make-up shoulder on the freehub when there's no spacer required.

IMHO...

[Paul]

This is a 7 speed cassette on an 8 speed freehub.

I have now found some old spacers with cut outs/bends to accommodate the rivet heads. They are narrower than the one I was using, but putting two together seems to do the trick. There's still some wonk in the sprockets, but nothing the floating jockey wheel can't handle.

(The spacer I had been using had no cut outs, which was causing the problem.)

But just putting 2 rivets in seems daft. Presumably saves a tiny amount of money 

[Feanor]

Hmm again...

That combination long pre-dates me, but that spacer seems to be quite big, 4.5mm!
https://www.sjscycles.co.uk/cassettes/wheels-manufacturing-7-speed-cassette-on-8-speed-hub-body-spacer-each/

And it doesn't seem to have any cut-outs to accommodate rivets, which seems strange.
Perhaps most 7-speed cassettes didn't have the rivets when those spacers were designed? Dunno.
ETA: I see the Jtec one listed at the bottom of that page *does* have the cut-outs.

Using two 1.85 spacers with the cut-outs will give you 3.7mm, which falls a bit short (0.8mm), which may be enough to prevent the lockring from properly tightening down on it.  This might be the source of the residual wobble.

If it were me, I'd probably file the missing cut-outs into the original spacer!
Or buy the Jtec one with cut-outs from SJS for £2.99:
https://www.sjscycles.co.uk/cassettes/jtek-cassette-spacer-for-shimano-8910-speed-body-to-7-speed-conversion-black/