I have a 1994 KX 125. My cylinder is worn and I need a new piston for when I get it bored. In the catologs it asks wether its an a or b cylinder but I dont know which one! please help!!! Thanks!
If you look at the outside of your cylinder, it should be stamped if it is an "A" or "B". It is usually on the back of the cylinder, facing the rear tire.
But what exactly do you mean by "and I need a new piston for when I get it bored"? If you are getting your cylinder over-bored (to a larger bore), then you will need a piston of that size, not the stock size.
Yep, if you are going to bore it, you will need a piston larger yet than the a or b. You machine shop can tell you what size to get to match your bore. Remember to keep all your receipts and any other related materials that have part numbers for when you sell the bike to another person. I gave all that info to the guy that bought my YZ, and he just about did cartwheels across my driveway he was so happy I had saved it all.
i am rapidly learning that the best way forward on these matters is to take measuments, especially if the bore has 8 years of wear on it. Any "good" repair shop should do the for free if they are getting your business on the parts since this reduces their chances of supplying the wrong part. remember if it is a plated bore, it will need to be replated after the re-bore. if you are looking for a good value for money tuner that will give you excellent performance to do this work, look no futher than eric gorr who sponsors this site.