Piston cutout shape

[jonno]

I have to replace a piston ,Asso,in my mugello 225.The one supplied is a Mitaka.The skirt cutout,underneath gudgeon pin holes are very different.Will this be a problem,and what function do they play?

[bazza3004]

Make sure the piston skirt in the area you mention (cut outs) matches the transfer cut outs in the barrel spigot at bdc.

[jonno]

So the different shapes have no effect?

[Scooterlam]

mark the cut outs and the ring peg positions on the piston crown, drop the piston with the arrow pointing at the center of the exhaust and run it down the barrel, what your looking for is the cut out over lapping the exhaust and the transfers. this will bleed and not work.
also check the pegs don't run over the trans or the exhaust the inlet isn't important as they wont run that low.
Also check the piston wont hit anything at the bottom of the stroke. you can measure the skirt length off your old piston.

[bazza3004]

As previous post states mark peg positions on crown with a felt tip or tipex and check they miss trans and ex ports . With piston at bdc make sure skirt covers ex port and also the skirts either side dont intrude into into the cut outs on barrel. If they do slightly i dont think marking and trimming this would do any harm as long as you only need to remove a little. If you do this make sure you clean up the skirt nicely and leave no rough edges.