Bike build help!

I am putting together a 4X/pumptrack/odd day Whistler ripper hardtail.

I am single speeding it and this is where I have run into a problem. I have BMX chain, rear gear but need a front cog that will fit a 4 hole crank arm but with teeth spaced for BMX chain. I have done some research and checked buy and sells but remain stumped. Does this exist?

So you have a 1/8" chain and cog?

AFAIK no 1/8" chainrings are available in 4 hole 104bcd.

You can run a 3/32" chainring with no issues though. Just make sure it's an unramped ring.

I am basically frankensteining 2 bikes together. I can do basic maintenance but the nuances of different drivelines is new to me.

3/32 is standard mountainbike chain? 1/8th is the the burlier BMX style?

Cassettes have "ramped" cogs?

I like the idea of a stronger driveline so would like to use the bigger chain. The BMX crank and front cog I have won't fit this frame though so need a (1/8) cog to match a 4 hole DH crank arm. Or my other option would be to pull apart an old cassette and put one of those gears on and go with a 3/32 driveline.

Thanks for dealing with my noobishness!

I run a 1/2" x 1/8" chain on a 14t shimano single specific r cog and a 32t, 9spd, steel, truvativ mtb chainring on my 4x bike. if you picked up any DH chainring you'll be fine.

3/32 is standard mountainbike chain? 1/8th is the the burlier BMX style?

Yup, that's correct.

You can run 1/8" chain on a 3/32" front chainring no problem. There's a little bit of lateral play but works fine. I'd recommend an unramped DH or SS specifc chain ring, although truth be told I've run with regular ramped chainring with no issues.

However, DON'T just take apart a cassette and use one of the ramped cogs on the back. That shit will skip the first time your chain is slightly out of adjustment and you crank on the pedals hard, and you'll smash your knee/balls on your stem. Bad times.

You need a proper SS cog on the rear. Cassette cogs can't properly hold chain without a rear derailleur tensioning it (even when they're new, but especially if you're raiding an old cassette. That 16t cog is probably the most worn out of the whole cluster).

another option is just use a mtb cassette, chain and ring. You can play around with gearing easily and pick the one you want. Works fine on my Cowan, just looks a little like a cheap bastard built the bike.

Bad times.

well, yeah the chain falls off occasionally, but I don't pedal hard anyway. It's more of a pumptrack roller bike.

i don't know if you are using a tensioner or have horizontal dropouts.. BUT just FYI the DMR STS roller was not wide enough ffor my bmx half link chain.