Can I take my Dura ace 7800 BB out of my frame and put in a treaded square taper bottom bracket?

Is there an adaptor for that?

Thanks!

All you need to do is take the 7800 bb out and put the square taper in.

Yes, but make sure it's the right size/thread. Most likely English 68mm.

You know you will need a square-taper crankset, right?

PS something like this. I think you also need to know your spindle length: https://www.performancebike.com/bikes..._1032278_-1___

I already have a Square taper BB and crankset so Im good there. I didn't think the square taper could fit in my newer bike. I dont know if its 70 or 68. I dont have a tool to take off the newer 7800 BB, but I have another external bearing BB laying around and it looks shorter than my square taper BB. Thanks guys.

OP...you need to provide more information or you will end up taking the bike to the shop to do it.
A picture of your BB...the year and model bike is a start. If the BB is BB-30...it can even be converted
to a std english thread square taper...but what a step backward FWIW.

Ok here is some more information:

I have this BB right now on my bike: https://www.performancebike.com/bikes..._1076736_-1___

I have a set of powercranks (powercranks.com) and a square BB laying around in my garage.
BB laying around is this: https://www.performancebike.com/bikes...551_1032278_-1

Can I just put this square bb in where the newer external bearing BB is now? Will it fit? Or do I need to get some type of adaptor?

Thanks

It will fit fine if both are english thread and BB and shell width match. Measure your BB shell length and the length of your square taper BB to confirm. If the square taper BB has a part number on it...google it to obtain the service information i.e. a PDF for the proper wrench to install it...whether it can be spaced if necessary to agree with your bb shell length etc. Instead of having bearings outside the shell of the BB, the bearings are integral to the square taper BB. But you are going in reverse really.

A suggestion is tho...keep your external bearing BB and get a shimano crank for it. Square taper just isn't as good although some with argue the point. Sell your square taper cranks on ebay and get a Shimano OB bearing crank and Shimano makes some of the best OB cranks because of adjustable axial play...just like they do very well in integrated BB-30/90 installations for the same reason.

External BBs thread into the same threads as square taper BBs. There are, however, different size shells that they can thread into, so you have to make sure that your 7800 BB is the same size as your square taper. Also, with a square taper BB you have the additional issue of spindle length, which can only be determined by knowing what exact frame/crank you plan to use. So basically, it could work, but there is no way to know for sure without more info.