Advice needed on crankset chain and cog

I'm building my first budget fixed gear and need some help. I have an old frame and have recently got some new wheels with a flip flop rear. When I fitted the wheels the single speed seems ok but when I turned the rear wheel round to be fixed, the cog appears to be a different size between the teeth and the chain won't fit.

I am not sure what to do next and do with some help. I will need to buy a new crankset as it is currently still the dual cog from the 10 speed. I'm guessing I need to buy a crankset, chain and rear fixed cog that all match? How many diffent sizes are there and what size should I be looking for?

I suspect that the freewheel cog is 3/32", the fixed cog is 1/8" and the chain is 3/32”.

Replace the chain with a 1/8” and it will work on both the fixed and free cogs.

You can keep the road (3/32”) crankset, it will work with 1/8" chain too.

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Cheapest solution is a new chain.
You should have someone check your bike in person at shop before you buy.

Thanks. I'll get a new chain and give it a try.

I have bought a new cheap crankset to get started and new chain. However the crankset doesn't appear to be as flush against the bottom bracket as it should. Should I tighten more or do I need a new bb too?

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As long as the crank sits tight on the axle, it doesn't really matter, if the chain line isn't out by too much.

Personally, i would put a new BB on there. They're not too expensive.

It is not obvious what is happening with the rear wheel, but for a normal track hub, the chainring probably would like to be much nearer the frame.

Where it is, the chain line is not right. What are the measurements I need to take when replacing the bb. I Know nothing about them?

I have now replaced the bottom bracket with what appeared to be a shorter but the cranks do not appear to go onto the bb far enough, I'm not sure what the problem is. Is it because I have got a badly sized crank set?

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Might be a mismatch between the taper on the BB and the cranks.

The bb I have bought is STD TAPER. Not sure what the crankset is I guess I'll have to replace one of these new parts again. How do I know what size I need for each they both look the same to me.