Engine rebuld

I have an nrg power 50cc and I'm rebuilding the engine,I've got the main bearings in but what is the best temperature to heat the inner race to,to fit the crankshaft without knackering the bearings.cheers for any help

 

just get it bloody hot, use some grease too, on both the bearing and the crank. it helps to have the crank in the freezer too

 

Cheers m8.ive had the crank in the freezer for a while.so I'll be tackling it very soon.