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PostPosted: Thu Nov 07, 2013 10:51 am 
Dirt Disciple

Joined: Mon Jun 25, 2012 6:59 pm
Posts: 25
Location: Southampton
Hi all, I posted this in the SS thread, but then realised I probably had a better chance of getting my query answered here, so apologies for the duplication...

I have just set my bike up SS. I've got a new chainring, a new cog and spacers on the back, a new chain, and a spring mounted tensioner (one that pushes clockwise, not anti-clockwise).

When I push down hard on the pedals (starting from stationary, climbing, etc) I get a horrible jolting sensation, accompanied by a clunk, and a weird squeak. This happens with every pedal revolution.

Why?

All bolts are tight and the chainline is almost perfectly straight. The BB is old. The freehub is a couple of years old and has a tiny amount of side-to-side play. But I didn't have this problem last week when I had gears and everything on the same BB and hub. The chain is possibly a touch too long, which because of the tensioner means the chain is only wrapping around the rear cog from the 8 o clock to 12 o clock position.

My thoughts are either the chain is skipping because I don't have enough of it wrapping round the chain, or I'm getting the jolting because the pawls in the freehub are skipping. I can't see how the BB or pedals could be causing the jolting.

All thoughts are welcome because it is doing my head in!

Cheers.


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PostPosted: Thu Nov 07, 2013 11:28 am 
retrobike rider
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Joined: Tue Mar 17, 2009 3:55 pm
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Location: In trubble'fsumthin r'uther....North Warwickshire
Likely not enough chain wrap around rear cog......especially if tensioner pushing clockwise.......get chain as short as possible to try and get as near as '30 minutes' wrap at the rear......


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PostPosted: Thu Nov 07, 2013 11:31 am 
retrobike rider
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Location: In trubble'fsumthin r'uther....North Warwickshire
A specific single speed chain will allow you to remove half inch links as opposed to one inch links and make the process easier......if your lucky you will get the holy grail of no tensioner needed, more difficult with vertical dropouts but possible, and the very best answer....


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PostPosted: Thu Nov 07, 2013 11:43 am 
Dirt Disciple

Joined: Mon Jun 25, 2012 6:59 pm
Posts: 25
Location: Southampton
Cheers Feetabix,

I'm going to try that this evening. With an 18 tooth cog I've probably got no more than six teeth engaged at the moment, which isn't a lot. Shortening the chain is definitely cheaper and easier than dismantling the hub and as it isn't going to do any harm I might as well give it a go.

I'll report back and let you know how I get on...


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PostPosted: Thu Nov 07, 2013 11:47 am 
retrobike rider
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Location: In trubble'fsumthin r'uther....North Warwickshire
On face value that's definitely the problem.....6 teeth in what is effectively a straight line is not enough for pedaling load......shortening the chain will add tension to the tensioner too, and as they say, every little helps!....


Last edited by feetabix on Thu Nov 07, 2013 12:08 pm, edited 1 time in total.

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PostPosted: Thu Nov 07, 2013 11:51 am 
retrobike rider
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Location: In trubble'fsumthin r'uther....North Warwickshire
You should notice the slipage at the point of crank rotation where torque is highest.......if regularly so then it will be that....I'd put my mortgage on it!.....


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PostPosted: Thu Nov 07, 2013 12:51 pm 
MacRetro rider
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I know mtb'rs prefer smaller chainrings but the larger chainring to larger ss sprocket that can still achieve your desired gearing ratio will give more teeth to the system and also help. For 2:1, 36:18 is better than 32:16 for this reason and even 44:22 is possible which really helps.


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PostPosted: Thu Nov 07, 2013 1:00 pm 
retrobike rider
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Location: In trubble'fsumthin r'uther....North Warwickshire
I agree......I run a 48/24 on one of mine, having butchered a rear cassette for the 24 toothed rear.....you will end up with a bit extra chain used and it does look like stevensons rocket, but it works and nothing wears out...... :D


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PostPosted: Thu Nov 07, 2013 1:10 pm 
Old School Grand Master
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Joined: Fri May 01, 2009 7:11 pm
Posts: 8479
Location: Fircombe.
Yup, sounds like chain slippage.
Setting up an SS for the first time is nowhere near as easy as it looks! We've all been there though!
The trouble is, "traditional" mountain bike chainstay length is 16.75" which is about a mm or two too long for most usable SS ratios. Even with a tensioner the chain is just to long to be "tidied up", as you will need to remove two links to make it (a whole inch) shorter. You can use a half link with KMC chains, or stray a cog or two away from the 2:1 ratio, or use a slightly stretched chain.
I use a 33;17 ratio on my Soulcraft with the dropouts slightly filed by a mm or so to accomaodate a fresh chain with no tensioner. This gives me a mm of adjustment too as the chain stretches.
You might find this useful. http://eehouse.org/fixin/formfmu.php

Have fun!


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PostPosted: Thu Nov 07, 2013 2:01 pm 
Retro Guru
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Joined: Thu Jun 23, 2011 11:25 pm
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Location: It's not easy being a dolphin.
Check for a stiff link too.


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