It is to install in the place of the starter and rotate the engine backwards. For carbon lock. If rotor motors are just lugged around town at low rpm and the cheapest fuel, they build up enough carbon to lock up the engine. the correct repair is to just rotate the engine backwards with this tool. Then just start it up and drive the crap out of it, and give the customer their car back.

 

Bob Mears

Supermarine Spitfire