Single speed conversion

hi all
apologies as this has sort of been covered in another thread but wanted to make sure...
i am looking to convert my 1970s peugeot 12 speed to single speed. is it possible to use one of the sprockets in the existing cassette and use some old spacers or should i get one of these...

http://cgi.ebay.co.uk/SINGLE-SPEED-ACS-sprocket-freewheel-cog-hub-16T-BMX_W0QQitemZ290168075799QQihZ019QQcategoryZ42328QQrdZ1QQssPageNameZWD1VQQcmdZViewItem

cheers

that won't fit ;) , just pull apart cassette and pick which one you wants and fill the rest of the space with spacers

IT depends whether you have (a) a modern cassette hub (as you say you do), where the cogs all fit on a splined body and held with a lockring OR (b) a threaded freewheel, where the freewheel mechanism and cogs are one unit that screws onto the hub. (original 1970s parts means you are (b))
If (a) - use a cog and spacers, (b) - screw-on freewheel (ACS / Shimano) will solve your problems.
http://www.sheldonbrown.com/singlespeed.html#freewheelhub

At a guess it would be more likely to be a freewheel if it is a 70s bike unless the rear wheel has been replaced. If it is a freewheel you can just replace it with the bmx freewheel you posted but you will prob have to redish your wheel to get the chainline correct. Good luck.

thanks very much guys, much appreciated.

Evening all,

I also have an old Peugeot - though its 1981 I think - that I am meaning to convert.

It's a ten speed (two at the front, five at the back). I have a particular combination that I run all the time anyway, and tonight the gods of fate have decreed that my rear derailleur should completely fail and basically blow up. Parts were left all over the road in the dark and in the rain, so I cut my losses. SO I'm thinking creatively about what I can do to get me through the rest of my uni term, since I'll be converting the bike within the next two or three weeks.

On a level of 1 to 10, how mad is it to simply remove all the crap, find a gear combination with a good chainline and shorten the chain to get a good tension? Horizontal dropouts mean I can get to a fair tension pretty easily, no? And gear... 8 (?) is perfectly in line, and I normally ride quite high in the gears anyway.

Any thought would be appreciated?

Ta

In theory you can shorten the chain to the best "in line" gear combination and it should run fine. This is the standard get-you-home-when-your-rear mech-snaps fix. There are usually a couple of problems that prevent this being a long term solution though. Firstly, the chain will often try to climb out of the selected gear as the gears in cassettes have a lot of features on them to aid shifting. Secondly, and most importantly, the chain is narrower and not as robust as a single speed and is likely to snap after a fairly short period of use, especially with the potential extra loading coming from constantly trying to move up / down the cassette.

Sounds like you'll have a great bike once the conversions done though.

The chain won't snap if it's been shortened correctly. I've had a bodged singlespeed cassette bike shift onto a larger cog and it bent the axle and dropouts, but the chain was fine. And I've also run 3/32 singlespeed for years and not snapped a chain yet.

But yeah, it'll work, but it might try to shift occasionally, especially if the chainline isn't perfect. Just work out what ratio you need (around 70" for flat city riding) and buy a cheap 3/32 freewheel for it (or 1/8 freewheel and new 1/8 chain). You'll need the tools to remove the existing block - buy them as an investment, or borrow off of the forum.

Sorry for the delay - I'm new here and didn't know it doesn't inform you of people replying to posts!

An update if anyone cares,

Sorted out the chain length so it wasn't binding and got a good chain line with 52t / 21t. When I first did it, it would jump out/off the gears especially at the front when I went over a drain cover (ouch) but now i think I've got it down and smooth. All sorts of noises came and went, but as I say... really smooth now and that's a couple weeks ago.

I don't think I have a lockring so I am looking for a new freewheel?

I would prefer to get my hands on a flip flop that has been properly redished. But I'm skint lol any advice on finding one?

What tools do I need to remove the freewheel? the converter that goes inside and a chain tool? Who can I borrow them from? is there a forum here?

@Clwydian - it's my baby!

Oh, and what if I run a 3/32 chain on a presumably 1/8 chainset? Will this jam the rear cassette?