How big can you safely bore a kx engine?

[mustangfury]

I have a kx 125, but i was curious for all the different sizes as well and think it would be good for other people to know too. 

I heard it was 40 over for a 125. Let's here some thoughts.

Thanks

[RoostDaddy]

what year are you talking?  (that way I can be sure to be correct)  If memory serves me right you can go to like 134cc or even 144cc just in bore.  Some even combined with a stroker were running around a 167cc.  Check out Eric Gorr, Max Power, or even Athena.

[junk man]

I have a 98 kx125 it has a LA sleeve iron sleeve. wiseco makes a std and 2 mm over size piston ( i think its a two ring piston ) with any over size piston you will have to trim the exhaust valve   stock bore on a 98 is 54 mm over size 56 mm stroke 54.5 mm 
I think the piston clearance is .003  its a little noise a idle. i use chevron 2 stroke oil 
also climb hills with it its never over heated or seized there good engines

i don't know if you don't have a iron sleeve    call LA sleeve see what they have to say

hope this helps   JM

[mustangfury]

my bike is a 1993. 

What part of the exhaust valve has to be trimmed and why? 

Also, i heard there is a difference between sleeved and plated when it comes to boring.  I am not sure what my bike is though.

[cbxracer30]

When you over bore the engine , if the power valves end up sticking out into the cylinder you have to grind them back so they don't stick out and rub or hit the piston. A sleeved cylinder can usually be rebored up to 4 times [ any small magnet will stick to a sleeved cylinder ] , a plated cylinder will have to be replated or sleeved. A plated cylinder transfer heat better and works better for long motorcross motos, a sleeved cylinder works just as well for everyday rider, we also use them for drag racing since our motors aren't lit that long. also all cr500's came with a sleeved cylinder.CBX

[YUNGGUNNAZ]

kx125 can be bored and plated using 4mm oversized rm piston.

[mustangfury]

so a magnet will not stick to a plated cylinder.

Do you know what material the plating or sleeve is made of for a kx?

I know plated holds up better and longer. If a sleeve is in there, can i still have it plated or will it have to be resleeved? I know stock they usually have them plated, but chances are they have resleeved or replated since then.

thanks for the input.

[Coop]

Sleeve's are iron and you get them bored if it gets damaged; Nikasil plating is for aluminum aluminum cylinders. If that is damaged the plating is stripped, the damage needs to be repaired (if possible), the cylinder then needs replated and re-honed. Depending if it's stock or bored obviously determines if you use the stock or over sized in either case.

Both have their pro's and con's and their fans that will defend both techniques feverishly, LOL. I have never had a problem with a sleeved cylinder; I do not race but I do ride off-road aggressively.