piston cracked??? any sugestions?

graeme · Renault 5 Driver Joined: 02 Jan 2005 Karma :

got the bike running, ticking over for 10 mins or so, went out on it riding for about 3-4 mins an the bike stopped,... got the barrel an head off an the piston had smashed at the bottom of it (think its called the piston gasket)

the man who is fixin it doesnt have a clue why this has happened
so i was wondering if anybody on here know why?????
help please thanx
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g.macdonald

tatters · Exxon Valdez Joined: 05 Jan 2004 Karma :

you mean the bottom of the pistons skirt has shattered like this?

Cause - Piston to cylinder clearance too large

Reason - If the piston to cylinder clearance is too large it allows the piston to rattle inside the cylinder bore, with time the piston develops stress fractures and eventually cracks (ushally only happens on a old worn out piston).
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Past:NRG50,AF1125(x2),NSR125RR,ZZR250,CX500,VFR400,KR1S,ZZR600(x2),CB400N,YZF1000(x2),KH125,Z200,FX400R,CBR954RR(x2)GPZ500S,GT550,VFR750F(x2),RD350N,XR650R,CBR600F,CB250,KDX250,YZF750R,CRM250,400EXC,KLR650,TTR600RE,DR350S,R100GSPD,RGV250,VMAX1200,DL650,KZ750 Present:G650XC,C12,CRF450X,1190ADV

graeme · Renault 5 Driver Joined: 02 Jan 2005 Karma :

yer thats more a less exactly whats happened.....
how con i prevent this from happening as the piston was the right 1?? thanx
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g.macdonald

tatters · Exxon Valdez Joined: 05 Jan 2004 Karma :

ethier the piston was too small for the bore, or the cyclinder is worn out.

make sure you have the correct piston size (think they come in A,B,C sizes) if you have just re-bulit it

also did you re-bulid it before if it sezied did you have the cyclinder re-plated or a new cyclinder.
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Past:NRG50,AF1125(x2),NSR125RR,ZZR250,CX500,VFR400,KR1S,ZZR600(x2),CB400N,YZF1000(x2),KH125,Z200,FX400R,CBR954RR(x2)GPZ500S,GT550,VFR750F(x2),RD350N,XR650R,CBR600F,CB250,KDX250,YZF750R,CRM250,400EXC,KLR650,TTR600RE,DR350S,R100GSPD,RGV250,VMAX1200,DL650,KZ750 Present:G650XC,C12,CRF450X,1190ADV

graeme · Renault 5 Driver Joined: 02 Jan 2005 Karma :

the crank seized on it so it had a new crank put on it

he showed me the barrel an said it hadnt been damaged from the piston crackin, an the barrel looked smooth an not scratches at all.

he has ordered a new piston for it, the malossi 70cc one so its the rite size for the barrel

i dont want to buy a new piston then that same happening to that piston, an just wen i want to sell it aswell.

so you have any other sugestons??

thanx a lot
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g.macdonald