Hi guy's, need some advice please, I have rebuilt a few wbx engines before and even run a 2.1 Turbo in my beetle. I have overhauled a 2.1 standard sizes on case crank & sleeves. When the case came together the crank turned freely by hand. I installed the engine and ran it for half an hour at idle. Then started revving up slightly to check for smoke, knocks, etc,etc and the engine locked up. however after 30 sec's the engine turns freely and will start first time and idles perfect. I reopened and saw that the centre main bearing caps have worked a little harder than the rest but nothing out of the ordinary, cleaned all up, polished the crank, fitted new mains. Now it will idle up to half an hour with 80deg normal, .5 bar oil press at operating temp. still does the same, locks up after half our. If I keep revs at 2300rpm it will lock up up after a minute. 1 minute later it will start up first click and runs like nothing ever happened but half an hour later, same thing. Using 20 W 40 Castrol as in all other builds. anybody had an experience like this before? Also running 1.9 carb on customers request. Please help!