does anyone use a single 39t chain ring on there crank, i am using a double crank that is set to the 39t but i am looking for a single 39t crank i have never seen one, any ideas?

cut three teeth off of a 42, sorry, i'm an ass

remove the big ring from your current crank?

its an old crank from the 70's so they are pinned together, i am just asking if you can buy a 39t single crank or if i have to buy a new double and take of the 53t ring.

well you could just buy the arms and chainring separately

Or buy a regular crank and ebay the 53

people make 39's all the time - that's a fairly normal chainring for ss MTB or cyclocross

My cross bike has a 39 single up front and nine in the back. It's an old Salsa cross ring that I picked up in the late 90's. I have a cross chain guard set up on it to keep it from coming off when I race. It's worked fine so far.

Might be able to find a BMX that size.

first step is to figure out what the bolt pattern is.

If the rings are pinned, it may be a cottered crank. They suck. The best bet is to get a new bottom bracket and crankset. Look for a square taper. The bulletproof cranks are good for the price. I think you can get them for about $30 on ebay. $20 for a new bb, and $15 for the chainring and you're good to go.