x5 4.6 is DIY timing job failure please help

[Elbrus]

Hi Everyone,
I decided to give it a try and do the timing overhaul on my failed timing guide rails.The plastic cracked after 154000 miles.So i replaced all 3 rails new chain gaskets and etc.I set the timing on cam shafts using the tool . and every time i was removing the blocking tool and spinning the crank shaft to test if everything was ok, one of the shafts (i think it was the intake) was slipping off ,and making click sound ,and timing was off again.I set the block again released and retorqued the bolts but it kept slipping off every time i was testing the timing . i was told it's the oil preasuure that will hold it back into place ,so i put back the engine .Tried to start, it was cranking but no starting, played with airmass sensor wires it started roughly and start making a rumbling/ clinging noise .And Of course codes came out Camshaft sensor position 1-4.5-8, air mass sensor ,throttle position sensors.
I put some videos on youtube if smb can take a look and put me in the right direction .
I Would Greatly appreciate the help, i know it's not an easy DIY but couple mechanics i talked to were complaining that it would take them 30 hours they are busy,i decided to give it a try myself.
Thanks
https://www.youtube.com/watch?v=0Kt-kD_4KuE
https://www.youtube.com/watch?v=A0frwFgba0k