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 Post subject: Single Speed Slippage
PostPosted: Thu Nov 27, 2008 10:02 am 
Dirt Disciple
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Joined: Thu Feb 28, 2008 4:20 pm
Posts: 86
Location: Newcastle upon Tyne
I have cobled together a cheapo SS bike to save the good bikes from the ravages of Newcastle's salty winter roads. (Fleabay bankrupt stock steel frame and forks £13.50 was a nice start.)

The problem I discovered last night when I finally finished the build is that the chain is slipping under the slightest pedal force. I suspect the chainring is worn but would appreciate a second opinion. The set-up is:

Son of Strongarm cranks with used Race Face 44t chainring
New Massi 8 speed chain (was going to be an 8 speed)
Onza 15t sprocket conversion kit
Mr C chain tensioner (down push)

I plan to use another crank tonight which has been fettelled with to put the big ring inside the spider. Does anyone have another theory about the slipping ? Ps don't worry about the ratio I'm not going near any hills with it yet!


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 Post subject:
PostPosted: Thu Nov 27, 2008 10:13 am 
Old School Grand Master
Old School Grand Master

Joined: Thu Jan 25, 2007 9:37 am
Posts: 4916
If the chainline is straightish, the tensioner is lined up properly and the chain is actually engaging enough of the 15 teeth on the rear sprocket, then it's the chainring.


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 Post subject:
PostPosted: Thu Nov 27, 2008 10:13 am 
Old School Grand Master
Old School Grand Master
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Joined: Wed Aug 08, 2007 10:35 am
Posts: 12267
Location: Penarth
In my limited experience I would say maybe its the chainring, but usually its the chain tension causing slippage. Can you adjust the doofer to push up...more chain wrap?
Carl


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 Post subject:
PostPosted: Thu Nov 27, 2008 10:21 am 
Retro Guru
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Joined: Tue Aug 07, 2007 12:22 pm
Posts: 2942
Location: Platsa, Messinias, Greece
I would have thought that any slippage is more likely to occur on the sprocket and not a 44T chainring where the load is distributed between 22 teeth (unless the teeth are practically non existent... :lol: ) or the chain is so worn as to be useless. (edit - sorry, it's new :oops: )

You'd be much better with the tensioner pushing UP - I can't understand why so many people have them configured to push down.
With a small sprocket like 15T you need all the chain wrap you can get - I've seen some set-ups where the chain only engages with about 30% of the teeth due to having too long a chain and a tensioner pulling down.
Run the chain as short as possible (even if that means juggling chainring/sprocket sizes) and just have the tensioner push up that last bit of slack.


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 Post subject:
PostPosted: Thu Nov 27, 2008 10:44 am 
Posh Mark
Posh Mark
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Joined: Wed Apr 18, 2007 2:49 pm
Posts: 5982
Location: As far from the city as you can be ....
Bent rear hanger? Maybe?

I had this on my Kili. Drove me mad.


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 Post subject: Ditto the above
PostPosted: Thu Nov 27, 2008 11:42 am 
Retro Guru
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Joined: Wed Dec 19, 2007 10:05 am
Posts: 961
Location: Brussels
I built up a hack for my father and had no end of trouble getting the gears to work - and mean work at all. I thought it was a simple component/cable pull issue but when I took it to the LBS we couldn't believe how far off straight the mech hanger was. If yours is as bad then I can imagine that the tensioner would be messing up the chainline.

I'd try to get that sorted first, and look for a new ring at the same time. They're always coming up cheap on here. Or try an under-chainstay tensioner, as seen on a few readers' bikes here?


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 Post subject:
PostPosted: Thu Nov 27, 2008 11:43 am 
retrobike rider
retrobike rider
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Joined: Tue Nov 11, 2008 12:28 pm
Posts: 4179
Location: rutland
bigggggg legs , feel the quad burn :lol:

fair play , thats a good road gear :D

its not chainline , if it was it would drop the chain . but to check take the chain off and run a piece of string from teeth to teeth ( you can wrap it around them ) and eyeball it from getting behind the bike , much easier to get it precise once the chain is out of the way

itl be the rear sprocket , only 7 of those 15 teeth will be engaged at the best of times , the large chainring ( most ss use a 32/34 ring ) will be putting the chain at a bigher angle and the tensioner pulling it further away

it tensions down because thats the way the spring is wound , it wouldnt work very well making it push up without changing the spring for an opposite wind . i wouldnt be surprised if they are a common spring and the opposite is harder( more costly to get old of )

but id hazard a guess the spring is the same as from a ad990 . if i get bored ill take one apart :lol:

a pic would help but for now drop the chain off the chainring , loosen the tensioner and turn it clockwise ( back ) and retighten , thatl add more tension to it so will push more chain onto the teeth


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 Post subject:
PostPosted: Thu Nov 27, 2008 12:41 pm 
Dirt Disciple
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Joined: Thu Feb 28, 2008 4:20 pm
Posts: 86
Location: Newcastle upon Tyne
Thank you for your constructive comments as always, I think the problem lies with the chain wrap issue. I did try to tension on the cheap. The Mr C tensioner was only a fiver and I think I'm suffering now :(

The chain can only be engaging a quarter is the 15 teeth on the sprocket so it looks like a push up tensioner is the answer. I have an old rear mech I might shoce on tonight just to get it working for my ride to work at dawn on Saturday :roll:

Thanks again for the input :lol:


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 Post subject:
PostPosted: Thu Nov 27, 2008 1:52 pm 
Retro Guru

Joined: Sun May 25, 2008 8:34 pm
Posts: 717
Location: Bristol
was just going to suggest trying an old rear mech to see what happens, and you beat me to it.

I have an old campag mech which is about to do those very duties!


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 Post subject:
PostPosted: Thu Nov 27, 2008 8:53 pm 
Retro Guru

Joined: Fri Apr 04, 2008 5:24 pm
Posts: 975
Location: South Yorkshire
As already said, I would say it is lack of tension in the chain and as a result not enough wrap around the rear sprocket. If the eccentric BB on my dialled works lose (only had to tighten it once since owning the bike) then the chain slips as a result of less tension.

Trevor.


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