kx 100 big bore

[rbadry]

i was wondering if any one can give me info on boring my 02 kx 100. What will i gain ? will it run hot ? What jetting i will need? and maybe any other info to improve performance

[Friar-Tuck]

 RBad,
 If you are gonna have to punch out the cyl to the next few Thousanth's  the biggest performance gain will probably be the fresh top end.   If you are going to a 110 or so you would certainly feel a difference along with possibly a carb change.   Moving up to the next oversize from stock may require a jetting change, but your carb etc should be fine.
   Does your cyl have a steel liner or is it  nikasil plated?  only reason I ask is there is quite a significant cost getting a cyl bored and replated as opposed to bored and fitted with a liner.
          There is a member here whose username is "Sapper".   
He has lots of expierience with the 65 to 100cc engines as he does all of his kids maintenance and engine work for their racing team. (MX)
 Probably the best advice I can give you is to get in touch with Sapper, He's a great guy and willing to share his knowledge.  If I had someone like that when I was younger and listened to, I could have saved years of frustration, money, and blown up stuff.

 Some information you might get ready for him is what kind of riding the KX100 is for, how much maintenence do you do, what type of rider do you consider yourself (honestly now) and of course how much money can you afford to spend.     
     Tuck\o/

[rbadry]

My bore is nikasil. The reason i am intrested is the bore is scored ( someone taking the bike who didn't know how to ride it)and i have to get it re nikasiled and i thought for the extra $50 they could bore it larger. The bike is for my girlfriend and she is a beginner( who i hope grows to like it) so i was looking at gaining her more bottom end.

[cbxracer30]

Over boring the 100 doesn't hurt anything nor does it make it want to overheat any quicker. Youi dont gain much, the bigger piston is heavier , your best gains would be from a stroker crank but this does require alot  more work , porting & head. the 100's that I had built to" race " never ran any better than the bigbore 80's , but then again they didn't run any worse also Eric Gorr really knows how to make them run.CBX

[gwcrim]

Whether it's worth an extra $50 is a matter of how much you feel like spending.

If you're going to let any beginner ride a KX100 you ought to consider a heavy flywheel weight.  That would be money very well spent to tame down the hit.

I bought my beginner girlfriend a TTR125 with an electric leg.  That's a much better beginner ride.

[Sapper]

The minimum overbore will take you to a 105. You'll feel a little more topend when on the pipe and not much on the bottom. Be prepared ofr some jetting R&D. A gearing change will help you in what you're looking for when you get it fixed up. I can say if you do stroke it, keep a stock bore. If not, you run up into the 110 or 112cc and then you deal with alot of reliability issues and it is meant to stay on the pipe all the time. It's a true racing setup and definately not a woods motor.

LA Sleeve can hook you up with a sleeve and replating. I had a cylinder done by them and it was great. We had a 54.50mm bore and it got scored, so they sleeved it and kept the big bore so we can still run 112. Wicked motor, but a wallet killer.