I have B&s engine 28r7071140-e1 and i need to know what is crankshaft torgue of those two bolts 6mm and 8mm

I am not sure which bolts you are talking about, but the Briggs Engine Check Chart (http://www4.briggsandstratton.com/miscpdfs/RNT/Engine%20Specifications%20Chart_ms3992.pdf) has many of the more popular torque listings, you might give it a try.