Cycling UK Forum

I've been recomissioning an older bike for a currently non-cycling friend and it's running a cheapo 6-speed indexed gear system consisting of very basic mechs and 'E-Z Fire' twistgrip shifters, with a 6-speed freewheel with the older style twisted-tooth design.

I've acquired a newer cassette rear wheel (with a 7/8-speed cassette body) from a friend but realised I can't just use a 7-speed cassette as the sprocket spacing is probably too different to work with the 6S shifter. The reason for replacing the original rear wheel is to get rid of the freewheel with the poorly-sited bearings and avoid the risk of axle failure, as my friend is not shall we say particularly lightweight...

Is there any way to devise a cassette which will work with 6-speed indexing? I guess 6-speed cassettes are long gone now, if they even existed, but could a 7-speed cassette be split and spaced to work, and where might I find 6-speed spacers?

Cheers,

Ben

Sprocket spacing for 6 speed is 3.5 mm. Shimano did make 6 speed cassettes back in the day but chances of finding them would be like rocking horse poo. Easiest option in my view would be to use a 7 speed cassette and fit new shifters, whch you can pick up for peanuts on flebay.

bgnukem wrote:I've been recomissioning an older bike for a currently non-cycling friend and it's running a cheapo 6-speed indexed gear system consisting of very basic mechs and 'E-Z Fire' twistgrip shifters, with a 6-speed freewheel with the older style twisted-tooth design.

I've acquired a newer cassette rear wheel (with a 7/8-speed cassette body) from a friend but realised I can't just use a 7-speed cassette as the sprocket spacing is probably too different to work with the 6S shifter. The reason for replacing the original rear wheel is to get rid of the freewheel with the poorly-sited bearings and avoid the risk of axle failure, as my friend is not shall we say particularly lightweight...

Is there any way to devise a cassette which will work with 6-speed indexing? I guess 6-speed cassettes are long gone now, if they even existed, but could a 7-speed cassette be split and spaced to work, and where might I find 6-speed spacers?

Cheers,

Ben

The 'newer' freehub will either be a 7s one or an 8s one; they are a different length. A 7s one is most suitable for use with a 6s system. 7s sprockets vary in thickness slightly; some are like 6s sprockets (nominally 2.0mm thickness) and some are like 8s sprockets (closer to 1.9mm thickness).

So

6s sprockets use 3.5mm spacers (for 5.5mm pitch) and

7s sprockets use spacers between 3.0 and 3.1mm (for 5.0mm pitch).

So you can respace a 7s cassette on a 7s freehub body to 6s spacing, using 3.5mm 6s spacers or by adding beer can spacers to the 7s ones. Because the mech position is defined by the limit screws in gear 1 and gear 6, and you will use a 7s compatible chain, you can leave the 1-2 and 5-6 spacing as per the 7s cassette if you like. This leaves spacers for 2-3, 3-4, and 4-5, i.e. you just need three thicker spacers of a precise width. You will also need some metal spacers between the #1 sprocket and the LH end of the freehub body and/or some spacers between the HG lockring and the #6 sprocket. These are not critical in width, provided the lockring tightens the sprockets properly you will be OK.

If you can get hold of the appropriate parts it would be useful to obtain a 'hybrid' 7s body (which will accept either an HG or UG cassette; these were made for ~1989 and ~1990) and a threaded 6s UG top sprocket; this will allow you to assemble 5 HG sprockets and retain them using the UG top sprocket.

A simpler alternative is to reduce the mech movement slightly per click, and to use six 7s sprockets at 7s spacing. Using the 'hubbub' style cable mount in the RD should work OK for this. If you leave all 7 sprockets in place, and adjust the mech to allow access to all 7 sprockets, you can use a barrel adjuster to decide whether you get to use the top six or the bottom six.

Or...... you could just use friction shifting....

cheers

Cheers Brucey.

Looks like the least hassle solution would be to try to vary the rear mech pull, if possible.

Failing that I'll need to buy and re-space a 7S cassette. Maybe get some spacers made up somewhere.

For the moment the original wheel and 6S freewheel will stay put!

Ben

I used to crush the spacers in UG cassettes just by pedalling hard in top gear. Basically the top sprocket would (for me) never stop moving entirely; it'd move, I'd think it was tight (and it was) but then the plastic spacers would slowly creep under the applied load, and (often months later) the top sprocket would move again. Repeat until entirely cheesed off. Other folk tell me that 'this doesn't happen'. Well it might not, for them. I found it a major PITA, since every time the top sprocket moved it threw the indexing out and eventually even the pitch of the sprockets would no longer be correct. duh.

Anyway to free myself of this nonsense I had to remake all my UG spacers (mostly 7s) in metal, which means I have still got a load of original plastic spacers in a box somewhere. I used to buy 6s cassettes (if they were cheap and/or had useful sprocket sizes in them) and then use the sprockets with my metal spacers. I think I have some uncrushed 6s spacers in amongst them, pm me if you would like a set.

cheers

.
post19 Feb 2019, 2:26pm

the least hassle solution

Like wot Brucey implied earlier, the least hassle solution would be friction shifters. You can use 6,7 or 8 speed, whatever you can find at the time, by simply changing hub spacers. And it's cheap.

Yes, but the new cyclist this bike belongs to will probably find it much easier to use indexed shifting properly, so they'll have to stay I'm afraid.

PM sent Brucey - thanks for offer!

Hi,

Brucey wrote:I used to crush the spacers in UG cassettes just by pedalling hard in top gear. Basically the top sprocket would (for me) never stop moving entirely; it'd move, I'd think it was tight (and it was) but then the plastic spacers would slowly creep under the applied load, and (often months later) the top sprocket would move again. Repeat until entirely cheesed off. Other folk tell me that 'this doesn't happen'. Well it might not, for them. I found it a major PITA, since every time the top sprocket moved it threw the indexing out and eventually even the pitch of the sprockets would no longer be correct. duh.

Anyway to free myself of this nonsense I had to remake all my UG spacers (mostly 7s) in metal, which means I have still got a load of original plastic spacers in a box somewhere. I used to buy 6s cassettes (if they were cheap and/or had useful sprocket sizes in them) and then use the sprockets with my metal spacers. I think I have some uncrushed 6s spacers in amongst them, pm me if you would like a set.

cheers

Not all the UG cassettes had a washer under the top cog?

NATURAL ANKLING wrote:Hi,

Not all the UG cassettes had a washer under the top cog?

no, but they all moved.

cheers

Hi,

Brucey wrote:

NATURAL ANKLING wrote:Hi,

Not all the UG cassettes had a washer under the top cog?

no, but they all moved.

cheers

Any technical explanations.
Grease.
Mammoth thighs
Large top cog
There were different colour spacers if that would make a difference not.
I will have to watch that one as I am using screw on UG 6S at the moment, though used before.
Its top cog screw on not HG lock ring on a seven speed set up?

All UG use a threaded top cog, at least the ones I used did.

Except for DA versions (which are slightly different) the top cog compresses all the other spacers. Metal spacers fixed the UG problem for me.

With SunTour New Winner freewheels there is a step in the body between sprocket 2 (splined) and sprocket 3 (threaded); in standard form the load on the #2 sprocket causes said sprocket to dish slightly (because the spacers either side of it are slightly different diameters), and there was a similar problem with the sprockets moving repeatedly (only this time it was the three middle ones on a 7s freewheel). After a few instances of this happening so badly that I couldn't get the chain to run on the #3 sprocket without touching the (now dished) #2 sprocket (and the gap between sprocket 5 and 6 growing ever-wider) I managed to fix it; my solution was to put some shims between the #3 sprocket and the shoulder on the freewheel body, so that the #3 sprocket compressed the #1 and #2 sprockets a fraction of a millimetre and then any further tightening of the #3 sprocket meant that it bore against the shoulder in the freewheel body.

The occurrence was similar in each case; everything would move, and then I'd think it was alright and it was for weeks (or sometimes months) during which time plastic spacers were settling (creeping), and then the threaded sprockets would move again. Needless to say getting the sprockets off afterwards was kind of tricky; I don't know anyone who owns chain whips with longer handles than mine.

cheers

what makes you think someone of xx weight is going to break the wheel?

Even in the extreme unlikelihood it occurs it's not dangerous, at that point then replace. You're making a lot of unnecessary work for yourself and twist grip gears are easy to use for novices. Why not leave it as is, worrying about what ifs for something that rarely happens even for 'big' persons seems very overcautious.

I've toured for years on 5 & 6 speed screw on freewheels with no problems

I don't think you should underestimate just how crummy the axles are in basic wheels these days. When the axle breaks it often takes out the rest of the hub with it, and sometimes the frame breaks too. If you look at what goes in the LBS scrap, you will quickly conclude that in such wheels, it is far more likely that the axle will break and that will scrap the wheel, than (say) the rim will wear out.

cheers

Hi,
I got one of those suntour sealed up screw on cog work of art, looks the bis but even after fixing the dished cogs what do you do with the axels, I know that outboard bearing, thanks for cassette hubs.