I'm trying to change my valve springs and I can't get this damn tool to work right. It's one of the low rise ones that compresses two at a time. I screw the allen bolts into the pushrod holes, make sure that the compressor is seated well on the retainer and start turning. It slightly compresses one spring, and does nothing to the other. Once it gets that slight compression on one spring it stops and doesn't compress anymore. I'll keep turning for 5 mins with no compression and eventually it makes a noise, and the one spring looses it's bit of compression. What am I doing wrong here? It seems very straightforward I don't understand why it just won't compress the springs.