honda xr650r oil problem
 

Hi, I was wondering if anyone out there can help me? I have an xr650r that knackered the bottom end due to lack of oil, after a full engine rebuild the engine was running fine with full compression. It was filled run then drained of oil twice, then filled with quality oil (1.7 litres). Within 350 miles the engine blew again, when the oil was drained there was less than .5 of a litre left in it. There are no external oil leaks and no oil in the coolant. This leads me to the conclusion that it must be burning the oil.
The rings and piston were brand new as was the gaskets, does anyone know if there may be a problem with the breathers and or oil pump that could cause over pressure which may be forcing the oil into the chamber?
Any views will be greatly appreciated as this is now getting expensive!
Cheers
Graham