I need to know if its possible to:

1) Use normal 7 speed freewheel and just pulling all the cogs off and use spacers and the like to get a perfect chainline, leaving the chainwheel alone of course
2) Hack a derailer into a tensioner

Anyone done either?
Trying to determine if I actually want to make my Trek 820 into SS. Its a TAD too small for me but might be perfect for tossing around, could be lots of fun!

1) will work if you can get a good chainline and most importantly if you can keeo the chain relatively tight. If it hangs at all, it'll skip the freewheel immediately. If you're going to toss it around though, I do suggest getting a proper hub/wheel or tensioner.

2) heard of it being done, never done it.

I have done 1 but not 2. If you disassemble the cassette you have your choice of gears down to 11 or 12 (try finding a 11 or 12 tooth BMX freewheel). You should be able to use the derailer but it would be ugly. I've seen knock off singulators here in Sacramento for $25. I bet with all those gears to play with you could find a combo that won't need a tensioner. There is a web site that has a calculator for just that, but I cannot remember it right now. Anyone else out tere know?

i had my mountain bike set up as a single speed on a 7 speed cassette using spacers and one cog. it worked fine. you can get non-ramped cassette cogs from shimano as well, which will work even better. not neccessary though. just as abstnr said, keep your chain tight! i was only using this trials chain guide thing as a tensioner and threw the chain once when it had gotten too loose. luckily it was when i was trying to sprint across a street with cars coming both ways. it threw my momentum off and i had quite a nice stack on the asphalt. i then used a 105 derailleur as my chain tensioner which worked perfectly. i just had to adjust the limits to keep a proper chainline, no hacking involved.

1) Did it to my old Trek 930 and now running it on my new to me Kona Lava Dome. Just brake apart the cassette and space out the cog with the spacers from the busted up cassette. You will probably need more spacers. I'd recommend getting a BMX cog like the Shimano DX ones rather than using a cog from your cassette. Make sure your chainline is perfect to avoid the dreaded chain throwing.

2) I used a BMX half-link to get my chain tensioned properly. Works like a charm. I've heard of people using derailleurs as tensioners...involves a shortened piece of cable and adjusting the derailleur. I've also seen a pic of someone who used an old V brake arm bolted to the derailleur hanger with a pulley attached to the brake arm as a tensioner. I'll try to find a pic or link.

Here's a link to a good SS FAQ page...https://www.mtbr.com/faq/ssfaq.shtml

Thanks! I'm going to try to do it w/o a tensioner, but with vertical dropouts that might be a pain.

OK I got the software now how do I measure the chainstay length properly? Want to do this conversion maybe tonight....

Measure from the center of your crank bolt to the center of the vertical drop, but don't go along the chainstay. Measure to an imaginary point that extends from the dropout s if your ruler was parallel to the chain. Did that make sense? Then input all your measurements into the gear calculator software and away you go. Like I said, if you're going to try to do this without a chain tensioner you may have to get a halflink, which woud then require a 1/8 chain. I think Spicer Cycles makes a half link for 3/32 chains though...have fun!

Can you post a link to the software?

https://www.teambigtime.com/software/ssConvert.htm

Progre-SS: Thank you!

Are you talking about a freewheel or a cassette? Never saw anyone attempt to dismantle a 7 speed freewheel. If your hub is freewheel and not cassette, grab a BMX freewheel and install.

I was just wondering how you break apart a cassette. I have tried without success. Are some cassettes built in such a way that they can not be broken apart ?

Thanks

I built a single speed out of an old 7 speed mountain bike with horizontal drops. NO chain tensioner on this project. I had to use 2 cassettes to get enough spacers to space out the rear hub, but the resulting chainline was perfect. THe cassettes were cheap and were rivetted (riveted?) together. I used a drill and a metal bit to drill out the squashed end of the rivets ( on the back side of the cassette), then I used a small nail punch and a hammer to drive the rivets out of the front side of the cassette. I went from a 7 speed to a single speed in a night, and because all of the parts I pulled off were low end crap, I was able to shave a few pounds off the bike in the process.

I have seen a derailleur set up as a chain tensioner. The guy just dialed in the limit screws to get it to stay where he wanted it (or thats what he said he did).

Have fun with your project.

I used a punch and hammer to take the spacer out of my seven speed freewheel, and then cut a piece of PVC pipe to make up for the rest of the space. I used a 14t shimano dx freewheel ($4, only project related expense) and I used the middle gear which is unfortunately permanently joined to the granny gear up front which is a 32t....with a homemade halflink (not recommended unless you have done it 100 times) I have a perfect chainline.....with a tiny bit of slack.....I am going to go out and get a 31 and a 30t sprocket to see if I can get a perfect chainline without a halflink one of these days, but for now, its fun, and noticably lighter than before considering the cheap shimano acera components I have been nursing along for the past 6 years!!!

I also had to hack apart my brake levers as they have integrated shifters, they're not the prettiest thing ever but it works....pictures to come when I get the sprocket and chainline thing sorted out!!!