top end rebuild advice

[williamjernigan]

I took my head off and my cylinder off and found that I need to have it bored out because the cylinder wall has scrathes where the piston has been rubbing up against it. The compression ring was good in it but he oil ring was bad. I is a stock bore right now but I am not sure how deep the scratches are in the cylinder wall so I want to get the right and good size overbore piston. I was thinking that if I get a .80 over piston kit would be 0.K.

[TheFontMaster]

.080 over would be more than enough. Unless they are really bad scratches .020, or .030 will be enough.

[kyex40047]

I have had mine bored three times and I just used an .80 piston on the last time, so I would go a little bit smaller

[zedicus00]

i go in .20 increments. and that cleans up sum pretty good size scratches.

[williamjernigan]

I think that maybe .30 will be enough to then. I just hate to order it and it not be big enough to take out the scratches. Also with it being bored .30 or say .40 over and it having boyeseen rad valve and reed spacer and graydon pipe with k&n filter, how fast should it be. I have never ridden a 250r.

[beak7707]

I would take it and have it looked at by the machinist and let him tell you how much will have to be removed. its always best to take as little as possible. If you jump all the way to .080 over you wont have much room for another rebuild if it needs bored.

[TheFontMaster]

How much boring would it take to put the motor at 275cc if anyone knows

[dober250R]

I think .080 over is 265.......................

[wilkin250r]

It would take some REALLY deep scratches to need more than 0.020 over.

If you are worried about it, then I would go through a reputable motorcycle or ATV shop (rather than a simple machine shop). With a reputable shop, let THEM look at it and, and THEY can order the proper overbore piston. That way, there's no chance of you ordering the wrong piston, or not going far enough.

The piston probably won't be all that much more expensive whether you order it yourself, or go through the shop. And boring is cheap, so that's not an issue. By going through the shop, you remove yourself of all risk of ordering the wrong parts and such. If THEY order the wrong parts, you don't pay for it.

[beak7707]

I would do what wilkin is saying.

[kyex40047]

Originally posted by dober250R
I think .080 over is 265.......................
No, 2.50 over is a 265,
3.50 Is like 278

[CHAR250R]

Call Lenny at Duncan Racing. 1-619-258-6306 I had my cylinder bored with the elite hone done to it, and a Pro X piston kit fitted to the bore.The bore was $75.00 and the piston kit was $95.00. I have been using Duncan Racing for 15+ years. None better. Make sure you do a pressure test before you ride it. An air leak might be fatal.

[baker250r]

.80 over is 265cc. if you are on the stock bore. I would bore it 20 over. first buy the piston and then send it in so they can match the piston to the cylinder. When you rebuild it, lube the pison in 2 stroke oil when u put it in the cylinder. might fowl a plug right awway, but its worth it IMO.