RCU Forums - Broken headers

Hi Dave,
Merry Xmas to you first of all.

Anyway I posted this in the pattern forum and would just like to know what you think.

I'm trying to figure out how I broke my first header yesterday. Its a Hatori 661 cooling header coupled to a hatori 660 pipe (I think its similar to the 791 header and 699 pipe?). The engine is a 110, on a similar mount to the MK one (engine bolts to aluminium beams, which are held by hard rubbery blocks, which are connected to the airframe). The pipe is mounted with the hatori beam mount that comes with the pipe at the back, and a dave brown (?) pipe mount at the front. The header has the MK mount with the plastic inner part sliced (as was suggested to me to let the header vibrate). The header broke where the flexi part starts. It had about 6 runs with the engine running. It never flew as I had problems getting the mount set up right. It was suggested to me that it could have been the pipe mount not allowing the pipe to vibrate back and forth with the header. I wasn't to sure about that because its the header that just slides into the pipe, allowing it to vibrate back and forth in the pipe inlet.
I did notice that the engine was vibrating at full throttle at a high frequency, ie the rocker cover was a blur, but I thought that that was normal for YS engines?
The other thing that I thought could have something to do with it was the cold, it has been under 0 degrees (celcius) for the last few days, and the shed where the model is stored must get very cold at night. Would that have anything to do with it? I did give the engine time to warm up before tuning it but the header might have cooled down again after I stoped the engine for 5 mins to get the belly pan on.
Any ideas as to what I can do to make sure the next one doesn't break?

Thanks!