Last night I had the need to replace one of the boom supports on my TRex700N so to get to the fixing bolt the plan was to undo the four caphead bolts and remove the muffler from the header fixed to the YS120.
A very straight forward and easy job you would think.

Nope not at all

These bolts have to be got at using one of those ball ended allen keys due to angle of attack not being straight on.

I managed to get two of the bolts out but found that the other two were very seriously tight.In the end this left me with two of the captive nuts that had been pressed into the back of the header just rotating.
No way could I now get these bolts out.
These nuts have a serrated edge so I would have thought that they would never be able to just rotate.

I was now stuck with a muffler that was permanently stuck to the engine.

Only way was to get the Dremel out and cut off the heads of the bolts.There was a danger here of damaging the muffler due to the angle that you can actually get the cutting disc in.Very easy to slip as well.

Ended up with the bolt heads off but then had to grind down further into the washer to get the header off.

I have managed to get the muffler off in one piece without touching it with the Cutting disc or the grinding attachment so that's a plus and have just had to order a new header set from Fastlads to sort it.

Just bad luck I suppose to start with and a bit of good in the end

Just don't overtighten those fixing bolts when you first get the muffler on.