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Chain half link removal on an IGH setup

Posted: 19 Oct 2016, 10:30pm
by gerrymcm
I have a half link in my chain setup, which I had to use due to my chainring/sprocket combination.

I would like to remove it as I think it's making my chain noisy and 'clickey' which is irritating.

I tension my chain via eccentric bottom bracket (EBB) but I can't simply remove the half link as it would make the chain too short and I can't add another full link as the chain would be too long or at least leave me no adjustment on EBB.

Long story short I need to change my chainring to a larger or smaller chainring but I don't know how to estimate what size is required.

Any advice or pointers please.
Thanks

Re: Chain half link removal on an IGH setup

Posted: 19 Oct 2016, 10:45pm
by andrew_s
adding one tooth moves the rear axle forwards by approximately 1/8 inch.

An extra tooth increases the chainring (or sprocket) circumference by 1/2", but only half the circumference is in contact with the chain, so that part increases by 1/4". To get that back with a fixed length of chain requires that you move the axle 1/8", recovering that much in each of the top and bottom chain runs.
It's not exact because the top and bottom chain runs aren't parallel to the chainstay and the angle changes with chainring size changes, but it won't make any significant difference for normal gears and a couple of teeth

Re: Chain half link removal on an IGH setup

Posted: 19 Oct 2016, 11:12pm
by Brucey
what Andrew says is quite correct but if thinking about this sort of thing makes your brain hurt you can use this;

http://www.machinehead-software.co.uk/bike/chain_length/chainlengthcalc.html

cheers

Re: Chain half link removal on an IGH setup

Posted: 19 Oct 2016, 11:36pm
by andrew_s
Furthermore, removing the half-link and shortening the chain by 1/2" means moving the axle 1/4" forwards. You can put it roughly back where it was by using a chainring 2 teeth smaller (see previous post), or a 1T smaller chainring and a 1T smaller sprocket, depending on the availability of suitably priced odd-numbered chainrings and which way you would prefer your gear range to move.

Re: Chain half link removal on an IGH setup

Posted: 20 Oct 2016, 11:49am
by breakwellmz
I always thought that having an EBB meant you didn`t have to mess around with half links and sprocket combinations to get ideal chain tension.

Re: Chain half link removal on an IGH setup

Posted: 20 Oct 2016, 12:08pm
by Brucey
it depends how eccentric it is I guess; if it has a throw of 1/2" (say) then it will always allow a new chain to be tensioned using full link length changes.

However it might not allow that and adjustment for wear through the chain life unless the chain length is either altered mid-wear, or set up using a half-link to start with, so that more of the full range of adjustment is available (when the chain is new) for use later on.

cheers

Re: Chain half link removal on an IGH setup

Posted: 20 Oct 2016, 12:16pm
by gerrymcm
thanks guys very helpful info and website.

I "think" my EBB has quite a lot of movement but I tried to set it up so I had maximum adjustability for the future to accommodate "stretch" ( as per Brucey's 2nd point above) but maybe in retrospect I should have simply accepted adding to the chain.

When I set it up I never paid much attention to the half link as I didn't think it would be a problem however now that I think about it the half link has been used/abused on a couple of previous bikes so maybe simply replacing will resolve the noise/click.

Thanks

Re: Chain half link removal on an IGH setup

Posted: 20 Oct 2016, 12:25pm
by Brucey
if you measure the chainstay length at its shortest then use the calculator (in the link I posted previously) to work out a chainring/sprocket combination that gives a chain length a fraction over (and still the right gear ratio...), and use that, you ought to be able to get set up so that you don't need to remove a full link part-way through the chain life.

FWIW it can be OK to use a half-link, but

- it isn't a good idea to re-use it several times over and
- even if you don't do that, it is unlikely to be made in exactly the same way as the other links in the chain, so may wear at a different rate.

So if you can find a way of avoiding the use of a half-link it can save a bit of hassle.

cheers

Re: Chain half link removal on an IGH setup

Posted: 20 Oct 2016, 1:15pm
by PH
And don't worry too much about having perfect tension on a hub gear, though I'm not suggesting you are. Anywhere between it not being taught and not slack enough to fall off works fine for me.

Re: Chain half link removal on an IGH setup

Posted: 20 Oct 2016, 1:56pm
by Roadster
Yes, I imagine having the chain too taut is far worse for general drive-train wear than having it a little too slack.
For this reason, I prefer to err on the side of slack when adjusting the chain tension on my Alfine 8 IGH.

Re: Chain half link removal on an IGH setup

Posted: 20 Oct 2016, 8:54pm
by gerrymcm
Thanks again folks for the input, I'll have tweak as per the advice (thanks Brucey) tomorrowhopefully.

I popped into my LBS tonight, which I dont do often and the chap in there mentioned that I had the chain facing the "wrong way". Apaprently half links are normally fitted with larger/external end of the half link facing forward and my one was the opposite way.
I'll flip it over in case it makes a difference and have a play with measuerments etc tomorrow and report back.

Cheers
Gerry

Re: Chain half link removal on an IGH setup

Posted: 20 Oct 2016, 9:25pm
by Brucey
the reason for fitting the split link one way round is simply so that it is less likely to snag on something (as the chain goes round) and then fall off.

It matters quite a lot on many chains, but not so much on bicycle ones I think.

cheers

Re: Chain half link removal on an IGH setup

Posted: 21 Oct 2016, 11:52am
by breakwellmz
He is talking about the half link not the split link being the wrong way round here Brucey.

Re: Chain half link removal on an IGH setup

Posted: 21 Oct 2016, 3:40pm
by Brucey
breakwellmz wrote:He is talking about the half link not the split link being the wrong way round here Brucey.


ah yes, silly me!

Possibly the half-link is less likely to snag on the chainring/sprocket teeth (during enagement) if it is fitted that way round?

cheers

Re: Chain half link removal on an IGH setup

Posted: 21 Oct 2016, 4:46pm
by gerrymcm
Sorted folks so thanks very much for the input.
I've replaced the half link and removed the split link (which I forgot about) and the noise is gone.

Also interesting re snagging of the split and half, that's something I forgot to change as I ran out of time.

Thanks
Gerry