any idea why number 1 piston has melted also need turbo info

[Grousebeater]

hi everyone could really do with peoples opinions.i have a 52 plate cupra r AMK with 129k i was driving steady at 80mph when i lost power i looked behind to see the motorway filled with smoke i got it home stripped the head off to find a small part of the piston had melted and has scored the barrel what would cause this any ideas i also had a feel of the imput shaft on the turbo it has about 1/2 a mm play up and down but about 2-3mm in and out is it time for a new turbo ? what would you do buy a new engine or rebuild the damaged 1 ? also whats your opinions on a holset HE221W turbo are they reliable is there much bhp gain any advice would be great

[grahams81]

Are the spark plugs ok ? - i.e the end hasn't fell of or small pieces of the ceramic fell into the bore and caused it to score the side.
This can sometimes happen if the wrong type (heat range) of plug has been fitted.

Was the engine tuned at all ?

Also depending on how handy you are it may be worth while just getting some forged pistons & rods and rebuiding it with new bearings, a second hand engine could go the same route but if you build it yourself at least you know its right.
If your upgrading the turbo you might want to consider forged rods either way as they are a weak point on these engines. Mine snapped @ 150k miles on a untuned well serviced standard engine.