BMX Cranks on a fixed

I used the search and found some things, but i need some advice from the ex/current BMXers out there.
I live in Brasil, and the availability of any kind of fixed gear/track frame is not that good, so to counter this i have collaborated with a BMX frame builder to produce a prototype frame.We used a track frame for the template, but have made it from 4130, it weighs in at 2kgs.....the only problem is that it has a mid sized bb.
This means i can only use BMX cranks, apart from the chainring pinch bolt unscrewing and the obvious weight dis-advantages, what other problems will i encounter using a BMX crankset?
As i have said this is a prototype frame, and anu ones that go into production will have a standard threaded bb, we just built with what we had available....
Thanks for any help......

http://www.londonfgss.com/thread21907.html

I am sure i heard Profile are making a Fixed specific crank now?

yeah they are.....but the cost of profiles here is stupid.......

Why would the chainring pinch bolt unscrew? Mine has stayed tight for 10 years. Some BMX cranks don't even have pinch bolts nowadays, they just have a stud that sticks out where the pinch bolt would normally be (a bit like on one-piece cranks).

You should actually be able to align your chainring with your rear sprocket more easily than with square taper cranks on a euro BB, just by adding spacers between the chainring and the bb.

You've already mentioned weight... so I won't go into that....

A Mid BB should last longer than a Euro because the bearings are bigger, thus stronger. Providing that they're decent quality in the first place.

Thanks Pastry, i had only read about the pinch bolt unscrewing due to backwards pedalling etc, and the extra stress of fixed gear riding.....but was unsure about the truth behind that. As for the rest of the advice thanks....

Thanks Pastry, i had only read about the pinch bolt unscrewing due to backwards pedalling etc, and the extra stress of fixed gear riding.....but was unsure about the truth behind that. As for the rest of the advice thanks....

well ive only ever pedalled forwards, so who knows, it might come loose when riding fixed, but thats easily sorted - just do it up tight in the first place and keep checking it. use a washer to help allow you to do it up tightly. grease on the threads will allow you to do it up tighter than without, but whether that will help it work loose, i dont know.

i think mine had this blue threadlock stuff on it, which helped it stay tight.

Or use a locking nut.

Or use a locking nut.

Eh? How exactly could you use a locking nut

in place of a chainring pinch bolt

?

Non Comprende.

i did wonder, but i figured it means that the chainring got drilled.....

Is this what you are looking for? http://www.sjscycles.co.uk/product.asp?pf_id=15019&src=lfgss

It's a banner add on the LFGSS web site. I've run a sealed bearing/aluminum cub BB on a BMX bike, not a huge weight penalty and trick looking.. Don't recall who made it though.

no, a mid bb is smaller than an american one, but thanks for the idea!

Iv tried standard bmx crank setup on fixed and the chainring bolt (dunno why people are calling this a pinch bolt??) came loose very quickly due to the backwards and forwards forces on it.
I now use a volume splined spider and it doesn't move a bit.

interesting.....do you use any other washers or bolts with the chainring bolt, or just the bolt?

There is no bolt, the spider engages with the splines on the axle as o the arms, there is no direct fixing between crank arm and spider/chainring.