Seat bolt problem and help needed

[gwynethh]

Need some help on a problem we caused: Unfortunately we have a galled front inner seat bolt that has broken away the hidden corresponding nut. Looks like we will have to use a cut off wheel to get the head of the bolt off and then figure what to do so the loose nut doesn't rattle around in the closed channel under the seat and come up with replacement fastening.

So the seat is in place, the bolt is 90% tightened. The "nut" hidden inside the square tube or channel below the seat has broken free so the bolt cannot be tightened or loosened. We do not have good access for a normal cut off wheel. Looks like a diamond dremel wheel would work to cut the bolt head off if we work at it slowly. We can then get the seat off again. That will leave the nut end to rattle around in the tube or channel and no way to secure the front inner side of the seat.

To remove the nut maybe we can drill a large access hole in the top of square channel and lift the nut and bolt section out. We do not have access to welding equipment to secure a new nut. What do you all think about a "Blind Insert Rivet Nut Rivnut"? We could probable rent the needed tool.

Comments, experience and other suggestions?