Hi, I've got a problem, when I was working on my polini 177's piston, it falled down from my hand and a small piece was broked. So..what do you think? I have to change the piston? or can I cut away a "ring" of piston bottom to make all the same? If I do this, the power will rise surely, but the reliability?

the red sign is the piece broked.

Thanks all,

bye Marco from Italy

Bearbeitet 26. März 200521 Jr. von FurlanPx

I would smooth the (red marked) area with the grinder (remove all sharp edges) and then let it as it is. If you want you can make the same cutout on the other side to be symmetrical...I don´t think this will affect reliability....(you should not remove the complete "ring"...thats too much material for no further advantage)

Bearbeitet 26. März 200521 Jr. von Andre

ups...position has changed? Doesn´t matter...

ok, and If I remove a "ring" like in this pic? I think it's better for the balance, and also for the performances, but in this case I don't know if it is reliable

LOL yes the position is changed, I signed the wrong position early ;) this is the right position of the broken piece

bye Marco from Italy

Bearbeitet 26. März 200521 Jr. von FurlanPx

read above...edit was there...

Keep in mind that the bottom of the exhaust port shall not be exposed when piston at top dead centre. If you remove the utter ring this may or may not happen. Also if you remove the ring all the way round piston skirt becomes pretty thin below the boost port window.

Just do, what Andre said.

If You cut down the whole ring of the piston-skirt, you would increase the inlet-timing too much.

Wrong balance should not be a problem. The broken and smoothed material of that edge is not more than a few gramm. It"s a cast piston, no forged one. So it"s not the very best in balance from the beginning .

vielen dank

hi, i have grind the complete ring below the boost port window on my 177 piston because of the same occasion and after a few 1000 km there is no sign of crack.

only to be precise, on my 177 piston there is no connection between the both ends of the piston skirt on the inlet side (like a ported 136 malossi one).

and this has got no effect on the timing, because a regular vespa motor is not piston controlled but "drehschieber"- or "membran"-.