Yz250 power valve carnage

I just had that happen for the second time on my 2012 YZ250.  By the time I found it both times the cross pin had pounded itself out causing the center valve to stop operating at which point I pulled the top end apart.  Both times only one tab was broken off.  The center exhaust valve is aluminum and the pressed-in cross pin is steel.  I suspect the tab breaks off over time after getting pounded thousands of times by the cross pin when the valve snaps shut, and then the unbalanced load from crosspin only hitting on one side eventually works the solid pin out of the bore in the valve.  Also the dissimilar metals of the pin and valve have different thermal expansion rates which may also cause the solid press-fit pin to loosen enough to move under these conditions.  After two identical failures in maybe 3-4 top end rebuilds, I'm putting a 4 mm x 24 mm long spring pin in there for the rebuild instead of the solid cross pin.  I'm thinking the spring pin fit is much less affected by thermal expansion.  Also the hollow pin may be a bit more compliant and may not break the ears off the bracket.  I believe the original Yamaha design had a spring pin in there instead of a solid pin.

I have also replaced that center valve at least twice over the years after the bump stop that controls the full open position broke off.  I never had a problem with that bracket breaking or the crosspin working itself out with the factory replacement parts, just the issue with breaking the open stop off.  I now have Cylinder works part in there that seems to be holding up except this solid pin issue and broken bracket ears.

I'll try and report back how the spring pin test works if I remember.

Almost every time I run across broken PV parts it's because they don't use the holding pin when installing or removing the PV linkage arm bolt. 

You're not that guy, are you? 

I'm not much a forum guy, just here trying to help after decades of experience with YZ250's.  Yes putting a small pin in the linkage is part of the process to tighten that small 8mm bolt head for the valve linkage under the side cover.  Last time I tried to break the center exhaust valve by not using that holding pin, I just snapped the bolt head off before anything else really cool broke (which was pretty disappointing).  I'm still looking for a quicker way to break that plate that doesn't involve putting a bunch of hours on the bike.