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PostPosted: Fri May 11, 2012 7:45 am 
Retro Guru
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Joined: Tue Aug 07, 2007 12:22 pm
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Location: Platsa, Messinias, Greece
cyfa2809 wrote:
Hmm i see but wont this be rather minimal?


Extremely minimal - as you say, chain "stretch" is just an accumulation of wear at each pin/bush interface rather than elongation of the side plates.

And just because I was waiting for the rain to stop, so that I could set about repairing the back door catch on my van, I've just measured the side plate length of a brand new KMC Z610HX chain and compared it to that of the old one that it's replaced.
No difference is my conclusion, or at least no consistent difference between old and new samples. I don't know what the total difference in effective chain length is because ICBA to take the new chain off the bike to compare with the old one.

Oh well, the rain's stopped anyway and the Fiat awaits........ :roll:


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PostPosted: Fri May 11, 2012 7:56 am 
Dirt Disciple

Joined: Thu May 26, 2011 6:03 am
Posts: 82
Location: Singapore, formerly Luton
The misses took a tumble from her bike and it bent the chain. as well as taking out some teeth from the chain ring. there was a bike shop nearby and they fitted a new chain. After that, the chain would constantly jump. initially i put it down to a dodgy cheap chain. I put my old chain from my offroad Marin hack on her bike and it worked fine. For a while the two bikes had to share one chain :shock: In the end i bought complete new drive train, chainring, cassette and chain (the original was very old), and everything worked again.

i just did the same on my old Marin, and tried the 'cheap chain' with my new chainring and cassette. worked fine no jumping. I couldnt measure much difference between the old chain and the new cheap chain, but clearly there was enough stretching on the misses bike that only a stretched chain would work with the worn teeth.


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 Post subject: checks
PostPosted: Fri May 11, 2012 8:19 am 
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Joined: Mon Jul 25, 2011 8:31 pm
Posts: 473
Well using the ruler trick, I checked the chain a couple of times and the lenght for 12 links was consistently around 11.6inches. Its the right chain as it says 9 speed on it.

I also took some pics of the front and rear cogs (attached) and tried to make sure that the rear derailleur was not bent.

I would appreciate any opinions on the quality of the cogs/ cassette


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PostPosted: Fri May 11, 2012 8:28 am 
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Joined: Wed Jan 18, 2012 12:37 pm
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Location: Derby
Like all things in cycling there’s a trade-off of weight vs strength…..why don’t we use 48 spoke wheels like BMX’s?

Hopefully the below photo will highlight my point.

The chain closest to the ruler is a 7 speed chain with just over 1% wear according to a park chain gauge, you will notice clearly the amount of stretch on the chain as the 12 inch mark is no where near a link pin and in that short length of chain the stretch is substantial.

The chain above that is a 9 speed with less than 0.75% stretch, it’s a bit difficult to tell from the photo but the 12 inch mark of the ruler doesn’t align with a pin centre either (on a new chain it would).

But the picture shows pretty well the effect of stretch don’t you think, just look how quickly the chain links stop being aligned!

Image


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 Post subject: Re: checks
PostPosted: Fri May 11, 2012 8:46 am 
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Location: Platsa, Messinias, Greece
samsbike wrote:
Well using the ruler trick, I checked the chain a couple of times and the lenght for 12 links was consistently around 11.6inches.


Well, you must have measured over 11.5 links (23 pitches) but straight away you have 0.10" of wear over that distance, which is getting on for 1% elongation (0.9% actually) so time for a new chain, I reckon.
That big chainring looks well hooked too, they get like that when you run a very worn chain on them and the greater effective length of the chain forces it to run higher on the teeth.


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PostPosted: Fri May 11, 2012 8:57 am 
Old School Grand Master
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Location: Antwerp, Belgium
I second Andy's opinion on the chainrings. Also, several of the rear cogs are clearly worn. The cutouts (not sure about the correct word) between the teeth are oval instead of round.

Time for a completely new drivetrain.


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 Post subject: thanks all
PostPosted: Fri May 11, 2012 9:00 am 
Retro Guru

Joined: Mon Jul 25, 2011 8:31 pm
Posts: 473
Best start looking then.

To get a new drivetrain, do I need to buy new chainrings for the front or a set with cranks?

thanks

sam


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PostPosted: Fri May 11, 2012 9:07 am 
Old School Grand Master
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Location: Antwerp, Belgium
A new outer chainring should suffice, but I'd give the inner one a good once-over with degreaser as well.

Judging by the amount of dirt on the rear axle and the general condition of the crankset and cassette, I'd say that the seller "forgot" a digit when he mentioned the mileage. I'm also pretty sure the bike has been used a lot in the rain and never had any proper maintenance.


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 Post subject:
PostPosted: Fri May 11, 2012 9:07 am 
Retro Guru

Joined: Wed Jan 18, 2012 12:37 pm
Posts: 425
Location: Derby
As sad as it sounds it may be cheaper to buy a new chainset than new rings. merlin cycles did have a sora chainset in the sale.

For road stuff i would take a, look at ribble cycles first .


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 Post subject: Re: thanks all
PostPosted: Fri May 11, 2012 9:09 am 
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Location: Platsa, Messinias, Greece
samsbike wrote:
Best start looking then.

To get a new drivetrain, do I need to buy new chainrings for the front or a set with cranks?

thanks

sam


Just new chainrings, unless you want/need an excuse to get some new cranks too :wink:

If you replace the cassette, chainrings and chain it'll be sorted, otherwise (like my Fiat van) you'll have to Fix It Again Tomorrow :lol:
Actually, I like Fiats......


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