Scimitar CVR(T) FV107 Diesel - starter motor not engaging

[EDA]

Hi all, new to this so please be gentle.

We have a Scimitar with the Cummins diesel conversion in pretty good condition, but the starter motor won't push its cog out onto the gear ring. When we toggle the starter, there is a healthy thunk indicating the relay is switching, but nothing else. When you manually lever the cog out onto the ring gear, the starter motor spins and the engine starts nicely. 

There is a "low power" circuit in the starter motor which is supposed to throw the cog out to engage, then this closes a circuit which provides full power to the starter motor to start the engine.

There are 3 inputs, one large which I assume is the main +ve for powering the starter motor, and 2 others which I don't understand.

Suggestions/help gratefully received.

[sirhc]

Sounds like the starter is sticky, maybe needs lubricating.

Petrol diagram but the same starter..

 

[teletech]

I had one where the Bendix assembly had gotten stuck from rust and issues, it just needed a couple whacks and wiggles on said assembly to get it to work occasionally and just using the starter has made it progressively more reliable.

I had intended to pull it off and go through it when I got a chance, but now it's so reliable there hardly seems a point.

[EDA]

This doesn't seem to have an external Bendix, it seems there is a "low power" circuit which throws the dog out onto the ring gear, which completes a circuit enabling full power to the starter motor.

It isn't hard to manually push the starter cog out (albeit a bit fiddly) so I"m not sure its lubrication, although I will try that. I'm thinking of applying 24v direct to one of the circuits to see if that throws the cog out as part of a fault isloation exercise.

Thanks all who have helped so fat with suggestions and diagrams.

[EDA]

Oh, and if anyone knows where I might source a gunner's sight for this, please let me know.