Broken piston ring(s) or a missing compression ring on #2 and #5 cylinders during assembly. Pull the #2 and #5 pistons and check for damage. Do a cylinder leakdown test before disassembly to confirm a pressure leak into the crankcase. If somebody else assembled the engine, RUN, do not walk away from his shop!
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!