SOURCE: Can I bore My 2001 yz 125?
It would be best to take it into a shop and have the machinist check it out before buying any parts, he should be able to guesstimate the amount of over bore required if it is at all possible, once you have this information, you can source the nessessary parts.
some of these type of parts are non returnable, best to play it safe.
hope this is of some help.
Ed
SOURCE: 87 yz 125t. bored .30'' over need 56.75mm Piston
yea, for most bikes they only come in .020 increments now. if your looking to freshen up the top end, then youll have to go to a 56.00mm piston. there will be almost no change in displacement or jetting from 55 to 56mm. if your replacing the piston, its best to have your cylinder bored anyways. since the worn cylinder walls may have adverse effects on the new piston rings, and they may wear a bit prematurely. a bore only costs about 30-40 bucks most places, and its cheap insurance. plus you will have the peace of mind knowing that your bore is matched specifically for your piston. I would definitely recommend a fresh bore.
SOURCE: YZ 125 Keeps burnig piston & Ring on Exhaust
only reason would be your running too lean. which causes more heat, which causes pre-gnition and pinging. Also if timing is off you create more pressure which in turn causes more heat
SOURCE: 2004 yz 125 std bore size,and what size do the
The std bore is 54mm and some available piston sizes are (Vertex Pistons)
53.93
53.94
53.95
53.96
53.97
SOURCE: Piston kit
try Dennis Kirk. They have a website. I suggest using the 800 number to place the order though for garaunteed customer service
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