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PostPosted: Fri Nov 12, 2010 3:45 pm 
Dirt Disciple

Joined: Sat Oct 16, 2010 12:39 am
Posts: 27
I'm repairing a friends road bike and he has an old suntour crankset on it. It must be from the early 80's. He complains that the chain doesn't go down onto the little ring. I confirmed this, the chain seems to fall between the two chainrings.

These chainrings are thicker in the body than in the teeth, but when they machined down the chainrings to make the teeth thinner, they did it on just one side, so the teeth are actually offset with respect to the center plane of the chainring. This bike is set up so that both chain rings face the same direction, and the teeth are offset closer to the frame. I am thinking that if I turn the small chainring around, this will bring the teeth closer to the big ring, and prevent the chain from slipping down between the two rings. Is this how it is supposed to be assembled?


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PostPosted: Fri Nov 12, 2010 5:00 pm 
Retro Guru

Joined: Tue Feb 23, 2010 1:56 pm
Posts: 1032
Location: West Yorkshire
Usually the inner chainring has rebates in the bolt holes to allow the inside half of the chainring bolt to be recessed into the ring. They will not be present if you flip the ring round. Are you using a modern narrow chain designed for 9/10 speed? That might explain the issue. 9/10 speed chainsets have the rings slightly closer together to stop this happening. At least Campagnolo ones do.

Mark.


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PostPosted: Fri Nov 12, 2010 5:16 pm 
Old School Grand Master

Joined: Tue Oct 09, 2007 1:55 pm
Posts: 8204
Location: New Forest, UK
Typically the rings have a flat face outwards. You should then see a recess on the rings for the crank bolts (right hand side for outer ring, left hand side for inner).

It sounds like both of yours have been fitted the wrong way round.


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PostPosted: Fri Nov 12, 2010 8:46 pm 
Dirt Disciple

Joined: Sat Oct 16, 2010 12:39 am
Posts: 27
I thought about the thinner chain, I doubt it's a modern chain though, this bike hasn't been maintained in 10 years so the chain is probably that old. It's a 6 speed drivetrain, what kind of chain should I replace it with?

Thanks for the hint about recessions for the bolts, I'll look into that.


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PostPosted: Sat Nov 13, 2010 1:14 pm 
Retro Guru

Joined: Mon Feb 01, 2010 8:57 pm
Posts: 774
You can replace the chain with any basic 1/2" x 3/32" chain. Somebody may have 'reversed' the rings to even out the wear, generally, there a recess for the chainring bolt on one side only or any stamping / marking etc would face outwards


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PostPosted: Mon Nov 15, 2010 4:04 am 
Dirt Disciple

Joined: Sat Oct 16, 2010 12:39 am
Posts: 27
Thanks for the feedback, the chainring was definitely reversed. I fixed that and now it works perfectly. Cheers!


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