So, the YZ450F that trashed the main shaft input bearing is nearly back together. Except that the engine builder doing the work phoned me to say that the STM Slipper clutch is missing the secondary spring stopper washer. I took off the clutch in the process of diagnosing what was wrong with the bike (transmission locked up), but I'm sure I didn't lose the washer. Not being familiar with the STM clutch I wouldn't have known about it, but I had a tray strategically placed while working and that caught any stray bits including the 6 balls. I had to pull the components out separately as the primary given gear/basket would not pull off until I did. It was jammed to the kickstart gear by a piece of broken bearing race.
I've emailed STM about a replacement, but I'm not too hopeful. It's part 003YAM007 on this photo of the installation leaflet (thanks a million to the person who posted this up on the internet somewhere!).
He also reports that a couple of the steel clutch plates are warped and need replacing. I'm wondering if someone may have had the clutch apart previously and left out this washer by accident or design. Might it reduce the secondary 'spider' spring pressure to create even less engine braking? Or perhaps leaving it out ended up warping the steel plates.
So I'm faced with buying a complete new (or used if very lucky) slipper clutch for the sake of a washer, or OEM hub, pressure plate, thrust plate, nut, lock washer, springs and screws to convert back to a standard clutch. My lad won't be happy about that as he complains about the 350SXF not having a slipper clutch. He brakes much later and harder then me and is used to just banging down through the gears without the clutch (this is on tarmac, running a road race full wet or a supermoto cut slick on the back).
I'll get the engine back rebuilt except for the clutch tomorrow, so I can experiment to see if it would work at all without the missing washer, but it looks as if it's unlikely to be back in action in time for the next speed hill climb as the OEM parts will take at least 10 days to arrive. If I'd known before I could have ordered them along with the new clutch basket/gear and main shaft