What glow plug do you have?
I'm not sure about this, but I'm beginning to think that the OS #8 likes a bit more juice to get hot than some other plugs. I'm far from sure on that though. Just a gut feeling from a few things I've seen happen at the field recently.

If you are having trouble flipping past compression, you might be hydro-locked. That's when the engine is flooded to the point that liquid fuel is preventing the piston from going up any further. Be careful, it's possible to damage the engine in this situation.

New ABC/ABN engines like the OS engines are frequently very stiff when the piston is at the top of the stroke. That's a good thing. If you're having trouble flipping it through compression, try flipping it backwards against compression, it sometimes helps.