Help diagnose engine seizure
 

I was on a dual sport/adventure ride a few weekends ago and seized my engine. I was about 20 miles in, all gravel/dirt roads, topped a hill, and the engine shut down. I hadn't gotten to full throttle over that 20 miles, and wasn't pushing the engine particularly hard when it died. I had mixed Stihl Ultra (synthetic) 50:1 the night before with 87 oct. I usually use Bel-Ray H1R, but have run the Stihl mix recently with no issues. The plug looked good, maybe a little rich. The piston/cylinder had a four corner seizure. The worst scaring was on the intake/clutch side, and exhaust/flywheel side. Those corners both had a piece of cylinder plating stuck to the piston. I've only put ~15 hours on this piston & cylinder since replating. Is this seizure from a flaw in the plating process or just a lack of lubrication? I quit racing enduros years ago, and was hoping to transition this bike into some dual sport use, but is this type of riding (relatively consistent speeds over longer distances) more than what I should expect to be able to reliably do? Also, any suggestions on where to get this cylinder replated?

Water pump failure? Impeller failure (stock are generally a polymer)? Low/no coolant levels? Extended period of hot resulting in insufficient piston/cylinder clearance and subsequent wear?

Could be bad plating. Images don't show up too large on my 'puter.

Doesn't look like lean seize. Looks like it had been wearing for quite a while (armchair view).

Water pump seems fine. Radiators were full, impeller looks fine. I didn't touch the cylinder for a few minutes after it locked up, but when I did, it wasn't hot.

Just curious, what does the top of the piston look like? Pic?

That plating does not look good at all, it looks like it has delaminated.

I don't see any crosshatch in the cylinder, was it honed to correct size after plating? Piston skirt ribs are also worn off was the piston clearance checked?

Anyhow these guys can fix you up.

http://www.powersealusa.com/

Top of piston picture is attached. It's been a couple years since I had this cylinder replated. I don't remember who did the work, I'm trying to go back over records. I sent a new piston in with the cylinder and cylinder was supposed to be plated to match the piston. I don't think I checked piston clearance or ring gap after getting it back.

That doesn't show any detonation. Heck its clean as. Like no time on it really.

Ring end gap would be interesting.

4 corner can happen with too tight bore or thrashed when cold.

I'd be sending it to a reputable plater and check ring end gap when you have it back.

So. . Is stihl like a chainsaw oil? I'd be going back to belray or similar.

looks like bits have come off the cylinder and jamed in there