you can did mine over the weekend and I decide to make a video. I have the timing tools but figure not all have the cam lock bar and the crank lock bolt. so tried it without removing belt and seems it is possible. now I just need to get video loaded. will be back with it soon
*****basically you turn crank until the two cams are settling where they pull the bottom half of the belt tight BUT leave top with slack. the video shows it better. but when your pass. cam is settling to where its wanting to turn CW(facing the engine) and the drivers' cam is turning CCW the top "v" of the belt will have slack and you can slip the thermostat housing out without hurting your belt!!
a8l 2001 d2 4.2l 40v v8 engine

 

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I've seen this before but every other time I do the timing belt (which will be next time) I put a new pump and thermostat on it.