chain advice

[Fladdem]

Me again, asking, probably, another dozy question.
I have built up a specialized P2 jump bike recently, single speed though, and I have snapped the chain about three times. I removed the broken links and then replaced them with spare links I removed when fitting a chain to my fixie, then another link would snap, I know this because the chain is white but I had silver links from my fixie, they are the same chain but obviously one has a layer of paint or something on.

The thing is, I have a seven speed cassette on the back wheel but it is a single speed chain. I can't quite get the chain line spot on, however on the 4th cog is where it is straightest, I thought it wouldn't be a problem because with a derailleur the chain is never spot on. I want to know if, because it is wider it requires a straight chain line, i.e. less flex in the chain. if so, can I put a spare 7 speed chain on and thus alleviate the problem because the chain can flex sideways a bit better.
The bike was originally meant to have gears but as I bought it as just a frame, forks, stem, bars, cranks and bottom bracket and I had the rest of the stuff in my garage, mostly, I thought i would just use the cassette and see what happens. The chain fit fine between the cogs, didn't rub on the 3rd and 5th cogs despite it's larger size and I thought I may need the bmx chain due to the torque, but it occurred to me on the way home that if it had gears it would still be put through the same torque and have a thinner chain and still do it fine.

After all this rambling, should I put a 7 speed chain on or a single speed?
Also, how tight should it be, I think it sometimes slips off the cog, onto the 5th because it's not tight enough and the chainline isn't straight but too tight and it would snap, although it has snapped a lot anyway.

Sorry, I always end up rambling on, on here.
Adam.
____________________
Current:1991 Honda MT50 (Soon to be a H100/MTX/MT5 hybrid), 1976 Honda Cub C70, 2005 Honda Varadero 125, 1993 Yamaha TTR250 Open Enduro , 2010 Road Legal Stomp YX140, 1994 Honda CRM 250 MK III, 1999 Cagiva Mito 125, 1992 Honda CB400 Super Four, Stomp T4 230, 1984 Honda H100s, 2009 Sym XS125K
Past:2003 Aprilia RS125, 1982 Kawasaki GPZ550(FREE BIKE!)
I'm having more fun than a well-oiled midget.

[Irezumi aka Reuben]

7-speed chain.

How to calculate chain length: https://bicycletutor.com/calculate-chain-length/
____________________
Pictorgraphicalfantastical

[Fladdem]

Thanks for that, I stuck the 7 speed on and it's working a treat, no more creaking as well! That's a bonus, it must have been rubbing. However, I have noticed it sometimes slips down a gear, towards the smaller cogs, I believe it's a tension thing, so I'll try slightly tighter on the chain.
____________________
Current:1991 Honda MT50 (Soon to be a H100/MTX/MT5 hybrid), 1976 Honda Cub C70, 2005 Honda Varadero 125, 1993 Yamaha TTR250 Open Enduro , 2010 Road Legal Stomp YX140, 1994 Honda CRM 250 MK III, 1999 Cagiva Mito 125, 1992 Honda CB400 Super Four, Stomp T4 230, 1984 Honda H100s, 2009 Sym XS125K
Past:2003 Aprilia RS125, 1982 Kawasaki GPZ550(FREE BIKE!)
I'm having more fun than a well-oiled midget.

[stinkwheel]

Convert it properly to single speed and use a single speed chain which is WAY stronger than a multi-speed chain if it's running straight and true. Replace the casette with either a spin on freewheel or a SS conversion kit and re-dish the wheel/shim the chainrings/replace the BB to get a straight chain line.

By using a deralieur you are robbing yourself of many of the advantages single speed has to offer. Chain should simply go round both cogs, be tight and perfectly straight.

Even if you have vertical dropouts, you might still be able to get enough tension by filing a flat on the wheel spindle or by using a halflink. I wasn't quite that lucky and need to use a singelator but you can convert a deralieur to do the same job. I fitted a spin-on freewheel, added a halflink and fiddled the BB to get a straight, tight chainline. The singleator stops it skipping if I am going up a REALLY steep hill.

This pic was taken just before my halflink arrived, the chain is WAY tighter now.
https://i48.photobucket.com/albums/f216/stinkwheel/CIMG0984_zps08721baa.jpg
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[Fladdem]

I am eventually going to convert it to proper single speed, using spacers slipped onto the freewheel but I was just using parts I had in the garage to build it too save money. It's got horizontal dropouts so no derailleur.

When I finish college later, I'll put a picture up of what I am trying to say.
____________________
Current:1991 Honda MT50 (Soon to be a H100/MTX/MT5 hybrid), 1976 Honda Cub C70, 2005 Honda Varadero 125, 1993 Yamaha TTR250 Open Enduro , 2010 Road Legal Stomp YX140, 1994 Honda CRM 250 MK III, 1999 Cagiva Mito 125, 1992 Honda CB400 Super Four, Stomp T4 230, 1984 Honda H100s, 2009 Sym XS125K
Past:2003 Aprilia RS125, 1982 Kawasaki GPZ550(FREE BIKE!)
I'm having more fun than a well-oiled midget.

[stinkwheel]

Sorry, I thought you were running them round the deraileiur still.

In which case it wants to be as tight as you can make it BUT be aware that you can get tight spots just like you can on a motorbike chain. For one thing, the chainring isn't always perfectly central on the crank spider but you can adjust it to be.

Sheldon Brown hads an article on how to do this (and lots of other advice on single speeds)
https://www.sheldonbrown.com/singlespeed.html#tension

Running the chain through a tight spot could well cause it to snap so set your tension with it on the tightspot.

Autoshifting is almost certainly a chainline issue.

You could also consider running a 1/8" chain.
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[Fladdem]

A 1/8 chain rubs on the bash guard a little bit, as you can see there is not much space there with a smaller multispeed chain.
https://i1302.photobucket.com/albums/ag134/Fladdem/P9140054_zpsda742fa8.jpg

The chain line is fairly straight, I don't know though, I was thinking of a spacer kit next pay day, and an 18 tooth instead of the 16 on there, also would shorter cranks help me spin up more? I am thinking of changing anyway, as they are 175mm and I catch them on the floor alot and they are beginning to make my chondromalacia patella flair up again.

https://i1302.photobucket.com/albums/ag134/Fladdem/P9140053_zpsa666b8d4.jpg

The disc is now rubbing on the caliper, I have tugged the wheel back, what can I do? It also looks like the disc or something is bent in the picture.

https://i1302.photobucket.com/albums/ag134/Fladdem/P9140055_zpsced1132c.jpg

And a token picture of the bike, when I finished it initially, still with white BMX chain and the old knackered headset.

https://i1302.photobucket.com/albums/ag134/Fladdem/1146371_4594338196763_1413053157_o_zps4ab5f234.jpg

Thanks.
____________________
Current:1991 Honda MT50 (Soon to be a H100/MTX/MT5 hybrid), 1976 Honda Cub C70, 2005 Honda Varadero 125, 1993 Yamaha TTR250 Open Enduro , 2010 Road Legal Stomp YX140, 1994 Honda CRM 250 MK III, 1999 Cagiva Mito 125, 1992 Honda CB400 Super Four, Stomp T4 230, 1984 Honda H100s, 2009 Sym XS125K
Past:2003 Aprilia RS125, 1982 Kawasaki GPZ550(FREE BIKE!)
I'm having more fun than a well-oiled midget.

[stinkwheel]

I'm not convinced at the straightness of that chain line.

You could always measure it up* but it looks to be a fair bit too close to the outside of the bike where it's going onto the freewheel. The chain appears to be runbbing your bash guard at the back but not at the front. If it was perfectly straight, it would either rub all the way round or not at all.

The crank length will effectively alter your gearing. When you spin-out is a function of the gearing rather than the crank length.

Crank length affects ground clearance and how far you move your legs while peddaling. Fitting shorter cranks without altering anything else will actually make the gearing steeper and harder to spin-out.

I'd suggest finding a gear you are happy spinning in with your current setup, plug the details into a gear calculator program (wheel size, crank length and sprocket sizes) to find out what that equates to in gear inches. Then enter the new crank length and fiddle with the sprocket sizes to achieve the same figure.

I've never had disc brakes on a bicycle so I can't help you there.

* For the rear hub measure locknut to locknut, divide by two then subtract the distance between the right locknut and the sprocket.

For the front measure the width of the BB, divinde by two the add the distance from the right side of the BB to the middle of the chainring.

Both numbers should be the same, or within a couple of mm. I aim to get it within 1mm.
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[Fladdem]

I actually like the gear ratio the next sprocket along, when travelling into the hub, but I couldn't get the chain to the correct tension, I'd need a half link, I run out of dropout before it gets tight and I can't get the chain short enough, it runs out of dropout the other way as well, i.e. the chain is too tight to make it all the way if I take a link out.

I did know something would happen if I changed just the crank length, wasn't sure what though. After thinking about it I suppose shorter cranks = less torque = harder to pedal which is the opposite to what I want.

I do think the chainline can be improved but I struggle, I was thinking maybe some spacers behind the crank on the BB to shift the crank out a bit.

I don't know why the brakes aren't like motorbikes, where the caliper bracket can slide with the axle. It's my first time fitting disc brakes, I tried to examine my other bike with discs but it's all slightly different and annoyed my head. I prefer rim brakes, cheaper, simpler, (for me anyway) nd just as efficient if you have a look around, If I spent the same amount on rims brakes as I did on those discs I would have had amazing brakes, but its a disc only frame.

Thanks for the measuring tips, gonna give it go I think.
____________________
Current:1991 Honda MT50 (Soon to be a H100/MTX/MT5 hybrid), 1976 Honda Cub C70, 2005 Honda Varadero 125, 1993 Yamaha TTR250 Open Enduro , 2010 Road Legal Stomp YX140, 1994 Honda CRM 250 MK III, 1999 Cagiva Mito 125, 1992 Honda CB400 Super Four, Stomp T4 230, 1984 Honda H100s, 2009 Sym XS125K
Past:2003 Aprilia RS125, 1982 Kawasaki GPZ550(FREE BIKE!)
I'm having more fun than a well-oiled midget.

[stinkwheel]

[Fladdem]

I have noticed he left crank, non-drive side, keeps coming loose, what can I do about that?
OK, no spacers on the BB, I think I will just go for something like this:

https://www.velosolo.co.uk/pictures/dscn4565a.jpg

This way at least I can get a load of different sprockets as well, and try to find a ratio I like.

I have a 34 tooth on the front and a 15 on the back, previously I thought it was a 16. It is way too hard for what I want. I was thinking maybe an 18 and a 32. but then maybe get a 17 and a 16 and test.

The crank is actually the sort where the sprocket isn't bolted onto the crank, there is a peg sticking out of the crank into a hole on the sprocket.

I took it to the local BMX track about two hours ago. The disc is bent, I have a new one to go on. The bike is fine I don't seem to notice the slightly bent chainline, although I did notice all the other bikes had the single speed set up properly, mostly MTBs there today.
____________________
Current:1991 Honda MT50 (Soon to be a H100/MTX/MT5 hybrid), 1976 Honda Cub C70, 2005 Honda Varadero 125, 1993 Yamaha TTR250 Open Enduro , 2010 Road Legal Stomp YX140, 1994 Honda CRM 250 MK III, 1999 Cagiva Mito 125, 1992 Honda CB400 Super Four, Stomp T4 230, 1984 Honda H100s, 2009 Sym XS125K
Past:2003 Aprilia RS125, 1982 Kawasaki GPZ550(FREE BIKE!)
I'm having more fun than a well-oiled midget.