Groove worn on R/H end of Crank - anyone seen before ?

[Phil-UK]

Hi

Had to pull my CB72 motor apart after breaking down in France and apart from the major problem I also noticed a "groove" worn into the R/H crank end as per photo.



Measuring the distance of the groove from the face of the starter chain sprocket it doesn't seem to line up with :-
1. The face of the rotor/starter clutch.
2. The end of the taper inside the rotor/starter clutch.
3. The ends of the starter rollers.

I'm guessing something metallic was caught up and wore the groove and fell out later or when I pulled the rotor off, but wondered if anyone had seen anything similar and if I should be checking anything else ?

The oil seal on the starter sprocket is further inboard so that should seal properly.
The motor has done about 16-18K miles.

thanks

Phil

[Phil-UK]

Wrong link ... this is the correct one:-

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Phil

[G-Man]

It looks like an undercut machined between taper and plain part of shaft. Perhaps someone did some machining on that shaft to rectify a problem?

G