Chainline accuracy

How accurate does it need to be? my chainwheel is about 5mm out from my rear sprocket, I'm running 1/8" chain, with a 1/8" chainwheel and 3/32" soon to be 1/8" rear sprocket. I can move the chain wheel to the inside of the spider and crimp the chainstay for clearance (not enough room as it is because its an old MTB frame), but would this be worth it, I do find it a little noisy. I started with a shimano 9speed front chainring which was quiet but it would throw the chain off when decending multiple kerbs and steps unless the chain tension was over tight.

5 mm is too far out 1 or 2 mm ok ish but you will throw the chain when you least expect it, like riding down a hill. Could you use a maller ring and cog combo to get the same ratio and have clearence?

I could do, but I'd end up with something like 36:13 and I'm trying to avoid such a small rear sprocket. with my 20st stomping through the pedals there is quite a lot of torque and transmitting that through 5-6 teeth on the back end worries me a bit. If I crimp the chainstay a bit more and move the 44t chainring to the inside of the spider I should get the chain line about spot on.

I just needed to know it was worth doing.

definitely worth doing IMHO

Being as you clearly have an oxy acetylene kit (because you brazed in your track ends with brass) I think due to your praticle skills and large hight and weight you should try building your own frame then every thing would be perfect. Or are you already doing this being as you have been looking at ceeway? Have you checked out the frame forum?

A switch to a 3/32 chainring/chain might mean less crimping and 6-speed chains are slightly better with chainline differences(I realise that you are going for 1/8th strong/niceness BillB)

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I'm going slow :) (and the oxy kit is a friends, I just go round and borrow it now and again, I have access to TIG too and we have a proper tube bender and notcher at our disposal)

I have the bits to build a fork first, once that is done and I've ridden on it a few months (and I'm confident in my brazes) I'll start on a frame. My plans started as a 29" mountain bike, fillet brazed and very chunky, I'm now thinking lugged flat bar road fixie :)

Yes I'm on the frameforum.

provenrad: I only need to lengthen the present crimp in the chainstay by 3/4" not a big issue and I'd rather keep my 1/8" rings and chain

sweet

5mm too far, 1 or 2mm okayish perhaps. i am going to swear at my latest build in a minute. could be out by up to 3mm

5 mm is too far out 1 or 2 mm ok ish but you will throw the chain when you least expect it, like riding down a hill. Could you use a maller ring and cog combo to get the same ratio and have clearence?

Could try some chain ring spacers from hub jub. Or just get some washers the correct size from a hardware store. This would save you needing to change your b.b.

I rode a set-up that was 5mm out for a few years, including (fixed) off-road. Never lost the chain once.

Fucking noisy though.