Kev has taken the heads off my SD for me (no space at mine at the moment) so they can go with Bash's to Bob Farnham for gas flowing.
At the same time he's pulled the barrels off because we'll be fitting the new hi comp pistons.
When he pulled the rear barrel off the first compression ring was in bits: about four big bits and a lot of small stuff. The piston looked like the broken ring had worn away at the groove in the piston doing some damage and there were two cracks in the piston itself.
We removed the piston and the 2nd compression ring and a section of the piston fell away! Looks like it has been broken for some time vibrating in place whilst slowly reducing the rings to dust and buggering the bore.
There is clearly a piece of piston missing at the edge where there is a lip at the edge of the indentation for the inlet valve.
Can't see where the damage started but there doesn't appear to be any damage to the head what so ever but the bore is badly damaged - the scoring is so deep you can feel it with your fingernails.
This, then, is why my bike made 125+ at the rear wheel in January and steadily less through the year.
If you have a look at these you will see just how close I came to lunching the entire motor.

Below is a series of photos:
In this one you can clearly see the piece missing from the side of the piston, the scoring on the skirt and the damage to the piston above the broken piece:



In this picture you can see the same damage from another angle:


In this picture you can see the piece missing from the top edge of the piston and the buckling around it:


Pictures of the broken off fragment from between the two compression rings (note the polished nature of the broken surface):



Picture of the piston with the broken piece reinserted

Unbelievable, but not completely unexpected. My valve seats and cams came apart before the first service.





KTM really needs to find better suppliers.

How many miles on the motor?

Nice!!!! I love carnage. Now it gets big boy internals.

Dude - that is seriously UGLY. Damn lucky!

Do you think it has been caused by running it with open throttle bodies?

What map and mods were you running?

That is definitely not due to open TB's. If that was the case and you swallowed something you would see lots of dents and dings up on your valves and upper cylinder walls. That is due to poor mapping and lean condition which has heated up the piston to start to fragment. Doesn't look like oil starvation due to everything being wet but that's a possibility too.

Those new slugs are going to look pretty in those honed barrels! I want some assembly pictures and some of your heads when done. Make sure your going into the lower end also while your there as there may be some left overs from what happened.

Might explain why the improved forged pistons they supposedly put in the SDR ... considering that SDRs don't make a huge amount more power out of the box.

I was thinking more a combination of dust, dirt, and grit being ingested over time rather than it sucking in a stone or something.

Bit off topic but while you have the engine apart is there any chance of getting the numbers of all the internal bearings?
Terry from Precisionbearings would like to do a full ceramic bearing kit for the SuperDuke but KTM wont give him the numbers.
I thought we should help him out as there are not many people who are willing to jump on board SD's.
Any bearing that you can give him will help.

I've started a new thread if anyone with bikes in bits want to help

very lucky you found that... any noise from the motor? when it was cold?

I'm with kevxtx on this one. Excessive ignition advance will pound the ring seats into submission.

Hey... There are some 990 barrels on Ebay for $199 if your in need of them. JAHU

Thanks for the tip: I'm watching them at the moment but I'm going to wait until Bob Farnham has seen the barrel and can tell me whether its practical to repair it.

As regards ignition advance : there is a change to the ignition advance on the maps I'm running but only at high revs but only within the bounds used by other people's maps on here - no excessive at all.
As regards running the mixture too lean: the front and rear are running different maps with the rear one following KTM's trend of running the rear pot slightly richer than the front so as to keep the temperatures even. The heads and pistons reflect this with the rear looking darker, almost black but with no appreciable build up so I'd guess from inspection we had them pretty much spot on.

TBH: I'm starting to think the real culprit here is a mixture of age, abuse and perhaps most importantly the fact that we raised the rev limit. I think that long term the stock cast pistons might be the weak link here when it comes to getting the most out of the motor. After all the SDR pistons are a far better spec.
Thoughts?

According to Bob Farnham the most likely cause of the failure is high revs.
The standard pistons from the cooking version of the SD are cast and not particularly strong it seems. Raising the rev ceiling to as little as 10,250 shortens piston life considerably.
The solution is after market forged or SDR pistons or, of course, don't rev it so high!