912 ULS - No Crank

912 ULS  2-01, SN 9571011, Hobbs: 3 hrs, Purchased 16/05/2019 (no longer under warranty)

Background: 

Fitted to a home built Sonex (A) - as happens all to often, this brand new engine purchased way too far in advance of use - warranty lapsed.

This engine has only recently been started for the first time. Full oil purge, as per Rotax instructions. After first start, carburettors balanced. Undergoing static (non flying) testing to fine tune cooling. On its half dozen or so starts it "caught" very fast, every time, including last start.

Today:

After some cowling modifications (surgery), I started the engine this afternoon - no problem. Cooling improved but still getting too high. Stopped engine and removed cowling, for further surgery. After about 1 hrs shut down, replaced cowling and tried to restart  - CLICK!.

Investigation has found:

Battery in top condition delivering expected power to starter solenoid/relay.

Starter motor tested  "open circuit"/no continuity - suspect damaged brushes.

Starter motor is HD varient.

Have checked out Heavy Maintenance, Section  80-00-00, Electric Starter and Illustrated Parts Catalog, Electric Starter, Section 80-10-00, 

I welcome all your analysis/diagnosis/remedial suggestions.