I recently traded my 97 Honda CR250 for a 2000 blaster. Took it out for the first real trail ride yesterday I blew a hole in the piston. I pulled the spark plug and it was crazy white. Pretty sure it was not getting oil. I was going to get rid of the oil feed system and just mix it, but did not have time. Oh well. My question is, I think that the engine has already been bored out .10 or .20. How much farther can I go? Also, what brand of piston should I get? Keep in mind I do not want to spend too much money on this. Thank you for the help.
Well I blew it up
- Thread starter JordanT
- Start date
A hole in the top of the piston is an indication of very high combustion chamber temperatures. It's a good idea to remove the injection system and start pre-mixing your gas and oil but a lack of oil will not burn a hole in the top of your piston. A lack of oil will seize the piston to the cylinder walls. Check for an air leak @ the crank seals, reed cage, cylinder base, carb or center cases, too low of octane fuel, too much compression, wrong heat range plug, lean jetting or overly advanced timing. Wiseco or Vertex pistons are the way to go. Make sure you know why this happened before you start putting money into the engine. If you don't fix the problem, you'll have two pistons with holes in them.
like was said the hole and the white plug indicates a lean condition. as soon as you get it rebuilt put a bigger jet in it. I just rebuilt my engine and was forced due to the already bored out cylinder to put a .090 piston in it from weisco. it cost me about $85 or $90 I don't remember for sure. but when you get a new piston just get the next size up to leave you room for future rebuilds if neccesary
if i remeber right the stock bore is 66 mm. the bores go up a .010 at a time whch adds a 1/4 mm to the bore each time.mines getting bored to 67.75 which is .070 over. if your only bored .020 or so you should have plenty of rebores left as long as the cyl isnt gouged or scored up to much.if im worng on the decimal points someone let me know 
When it comes to your piston youshould want to spend a little extra cash on a Wiseco. To tell the size your piston is now it should be marked on the top of the piston. STD for reg bore 66mm, then it should say .25mm or .50mm and so on. You can go to 80 over 2.00mm from stock.
As mentioned you should check for airleaks..
Also welcome to the site...........
As mentioned you should check for airleaks..
Also welcome to the site...........
yamaha dealer here says 100 over without overheating issues
but i would go with a vito's big bore kit and a stroker crank instead... good hp increase
but i would go with a vito's big bore kit and a stroker crank instead... good hp increase
The problem is money. I will be spending the money on a good wiseco piston. I will keep you all updated with what happens. I will be taking it into my engine guy this week. I will also be removing the oiling system, but have a question. There is oil running through the ports along the outside of the piston walls, how does oil get in there if I do not have the oiling system?
