SEF-R 300 - Crankcase Damage at Swing Arm Pivot

[Tlbikenut]

Hi,
I’m keen to understand what may have contributed to this failure in order to prevent any repeat in the future.

Anyone experienced or aware of any similar failure?
Anyone able to shed any light on the potential cause?

2017 SEF-R 300 - 166 Hours

Engine mounting bolts weren’t loose
Swing arm bolt wasn’t loose
Swing Arm bearings hadn’t seized or collapsed but were slightly rusty
Green Lane use since being purchased second hand and No major major get offs. (Worst being a couple off sideways offs at low speed on relatively tame rocky climbs).

[bad-mod]

There looks like some historical cracking there

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[erdat]

A fellow Sherco rider had a similar damage due to the rear spring hitting the case, because of bad linkage bearings,
Erdat

[Tlbikenut]

All suspension bearings were serviceable, definitely not enough slack for the spring/shock to be hitting the crankcase.
And I agree the crack clearly does show some signs of having been there at the bottom for some time as it is discoloured, but what could have caused it to crack and subsequently fail.
I've repaired a couple of XR400's with corrosion issues which cause this but as can be seen here there is very little corrosion in this instance.

[bad-mod]

I guess if the frame was flexing with swing arm side loading that is the only place It could go, It would take a bit of force to break that though.
I guess another option could be that the maxhining tolerance was to tight when fitting the steel bush, that could of weakened or stressed the casting.

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[esam]

Any possibilities for overtighting the swing arm bolt?