My BM Pika has always been stiff, working the blade with oil didn't help much. The other day I needed a machete but used my BM pika to hack out a few small knots in some tree limbs, as I chopped I noticed the blade rebounding against the back spring, I put the Pika away got a machete to finish the job. That evening when I pulled out the Pika I noticed I could open and close it much easier than before, I must have bent the spring slightly but I'm happier with it now than before. I don't recommend this as a fix to all stiff BM Pikas but it worked for me. Just thought I'd share my experience. 
Bob
Bob