There is a spec for how far out the ring gear? needs to be from the block. Did you check that? There was also an update done to some starters and they can't be used with some engines. I forget which way it is exactly. I read it on a pamphlet that came with my rebuilt starter
how longs it been since it was previously started? maybe the starter is just a little sticky. the solenoid makes the gear come out, so if its cycling on, it should be trying to turn the flywheel.
It was the ring gear and starter (and gearbox) from the petrol, started maybe a week or 2 earlier, and it was perfect then. Put everything on as I took it off. I will have to have a good look at it again tomorrow