After reading your "What did i stuff up here" story
its questionable that the ring pin has gone, if it was not present at all the ring would have rotated on the piston and the ring would catch in one of the ports & major damage occurs ! prior to seizing like this.
or the ring may of claimed over the ring pin as the ring & bore would have to be very very worn.
Appears to more like a heat issue, whats the top of the piston crown look like?
Was the bike pinging, its a death rattle under high load.
Did it blow at high ground speed ?
Is the carby clean, no blocked jets? is there water in the fuel bowl, main jets may not pass water, surface tension is the issue!
Was the bike running a high idle speed after a run / coming to a dead stop, then returning to slow idle after a short period or even stalling, this is likely a crank seal & or air leak at base gasket or intake manifold.
Not that this bike was likely blowning massive smoke ( bore looks very dry & lack on carbon deposits ), but if it was the primary drive side crank seal leaking, drawing trans oil and burning it, which once the seal runs dry, it also sucks air ( lean) what the trans oil comsumption like?
Husky mag motors do this ask "Tossa" mag crank case bikes that have had water sitting in them at some stage equals shitty cases.
If the piston crown is damage in the centre like a hole is forming, its likely the heat range of the plug to hot and lean mixture.
Comp bikes "NO" 7 or 8 NGK hot range plugs , 9s in air cooled bikes & 10s in water cooled, if it needs a 8 or less to run dry its to rich, like wise other brands near coldest plug or coldest only.
If the piston crown has alloy splatter over its detination, poor timing.
If the piston crown is blown away at the front / exhaust port its pilot jet is to small, the bike also would of been pushing your though the corner like its lean. but probably returned to idle well prior to failure.
If the intake skirt of the piston has seize marks its lack of oil. wrong oil ratio !
If both sides of skirts of the piston have seize marks it could have cold seized ( not warning up the bike and thrashing it from stone cold )
Rings end gap that is to close ( fresh rebored motors ), also cause engine seizures, more so at the exhaust brigde in the cylinder & piston in that area. not that this is a bridge port motor.
Was the bike kicking back though the kick starter, if so its to far advanced timing. also leans out the bike and run hot.
Bikes that are hard to start may have low float level, this also leans out the pilot circuit, guys that have leaking float needle valves that bend the float tab are also making they bike hard to start. low fuel level equals lean pilot jet.
Just a few things i have seen, found or experienced on my own bikes and clients over the years.
I have found as main jets and jetting goes, engine temp drops as the jet is close to been correct, wrong jet high temp. as the engine gets close to the correct jet the engine cyl head temp drops, if it begins to rise again its getting the wrong way, either rich or lean!
Capacity has also an effect on air cooled cylinder head temp, small 125cc around 85-95 deg, 250cc 120-140 deg, 500cc very hot, close to 190 deg, on this bike its one jet size out and blows passed 205 deg, should be running methanol, all temp measured three laps at Narrogin.
Regards Gibbsy
