If all else fails, you can cut a hatch in the top of the fuse right behind the firewall to access the tank.
I doubt that the spinner grooves could make it vibrate. But the fact that it has a vibration doesn't sound good. Try this, take out the glow plug and spin the prop with your finger. Does it spin smoothly? Or do you feel a snug spot? It may be snug at the pistons uppermost point, but it should not happen anywhere else in the rotation. If it does, you could have a bent crankshaft.

How much impact did the engine take when it hit the tree?