Well,
After waiting for dealer to get parts, I decided it was time to take bike "home" and sort it myself. Dealer's mech had cleaned everything well and kept it sorted between left and right.
Got 2 new pistons, gaskets and two 2nd hand good cylinderheads from Paddy Maddock, brought these things back here on 1st Nov and stuck it back together slowly and carefully. Paddy had printed out the reprom pages that I needed and I got a copy of reprom from one helpful inmate. Funny part is I found a Haynes book for this model ('10 !) in Halfords in WEXFORD!! Go WEXFORD!!
The tricky parts:
One dowel lost, made one 6mm by 14mm but cutting the stem off a grinding burr.
Putting enough sealant on the base gasket - but not too much!
Getting gudgeon pin circlips on - need good pliers.
Setting camshafts (should have special tool and gizmo to set the chain tension) but result seems pretty good.
Checking valve clearances bearing in mind there are 8 and I have only 8 shims.
Test ride today, then checked the cams and shims again. Swapped two shims on each side (top for bottom) to even out the clearances.
Running well, bit frustrating not to know the real cause of the burnt valves and the melt-marks on pistons. Both pistons have similar marks on inlet valve sides.
The issue happened at 48,500kms after say 10 minutes running at 180kph, +45C, 800M above sea level. Slowed down for checkpoint (walking speed) and then when I went to pull away, lack of power, weak running on left side.
Bike was in dealers for brake and clutch fluid change at 45,000kms and I asked him to check the valve clearances - never done since 20,000kms. He said all valves were in tolerance. Hard to think what he could have done that would lead to the problem although the co-incidence is remarkable.
I do recall that when bike was new, I rode about 800kms and realised it was not running properly. Too vibey. That is when the dealer got the tool for setting the cams properly - this was done and no prob after that.
Resigned to thinking it is a combo of hot weather, fuel quality, lean running and maybe valve clearances tighter than should be for good heat transfer.
I plan to fit Booster Plug to richen slightly and to leave off the cam-cover guards to let more heat out - let's see.
Thanks for REPROM to you-know-who!!
(The oil is Castrol Edge Sport 10w60 - in case anyone asks..)
Next job - change battery in rear-wheel TPS sensor..
http://www.youtube.com/watch?v=Mpjz0cDjnK4
Bin