Hi Guys!
I am just about to rebuild my 1991 YZ250 Engine after it siezed this past riding season (first season under my belt on a mode!). It siezed because I blew the O-Ring and drained the Rad dry.
I took it into the local shop and they said that they could bore it over .010" to fix the scoring the piston left on the cylinder. I have a couple of questions, if anyone knows the answers I would be really gratefull!
1) I took it to another shop and they said that the stock sleeve is a plated sleeve. From what I can understand plated sleeves can/should not be bored out. I am not sure if the current sleeve is stock or not so I am not sure if it is plated or not, is there a way that I can tell if the sleeve is plated or not? I would assume that the bike shop would be able to tell, but I wouldn't mind knowing so I know if I am going to get ripped off or not. I stuck a magnet on the sleeve and it seemed to stick, not sure if that says anything or not.
2) If the sleeve is not plated and I am able to bore it .010" over, do I have to modify the head to accept the larger bore? The bike shop said that I did not, but I remember reading somewhere that older YZ250's had power issues (Squish Band?) with overbored cylinders. Does anyone know of any issues that I should be aware of when boring out a 2 stroke?
3) If I bore it over, will it affect my carb jetting?
4) The head looks OK, I measured it for warpage as per the manual that came with the bike and it seemed OK, but I noticed that there was some pitting on the intake side of the head. Does this affect performance? Is this just normal wear and tear or should I do something about it while I have the engine apart already? The piston crown seemed OK, a little grey with some speckles in it.
5) Since I have the engine apart, does anyone have any suggestions of any inexpensive ($100-$200 range) engine changes that I can do to make it run faster? There is already a Pro-Circuit pipe on it.
Thanks for any help guys, I am really looking forward to riding this year. The weather up here is starting to look promising!
Corey
I am just about to rebuild my 1991 YZ250 Engine after it siezed this past riding season (first season under my belt on a mode!). It siezed because I blew the O-Ring and drained the Rad dry.
I took it into the local shop and they said that they could bore it over .010" to fix the scoring the piston left on the cylinder. I have a couple of questions, if anyone knows the answers I would be really gratefull!
1) I took it to another shop and they said that the stock sleeve is a plated sleeve. From what I can understand plated sleeves can/should not be bored out. I am not sure if the current sleeve is stock or not so I am not sure if it is plated or not, is there a way that I can tell if the sleeve is plated or not? I would assume that the bike shop would be able to tell, but I wouldn't mind knowing so I know if I am going to get ripped off or not. I stuck a magnet on the sleeve and it seemed to stick, not sure if that says anything or not.
2) If the sleeve is not plated and I am able to bore it .010" over, do I have to modify the head to accept the larger bore? The bike shop said that I did not, but I remember reading somewhere that older YZ250's had power issues (Squish Band?) with overbored cylinders. Does anyone know of any issues that I should be aware of when boring out a 2 stroke?
3) If I bore it over, will it affect my carb jetting?
4) The head looks OK, I measured it for warpage as per the manual that came with the bike and it seemed OK, but I noticed that there was some pitting on the intake side of the head. Does this affect performance? Is this just normal wear and tear or should I do something about it while I have the engine apart already? The piston crown seemed OK, a little grey with some speckles in it.
5) Since I have the engine apart, does anyone have any suggestions of any inexpensive ($100-$200 range) engine changes that I can do to make it run faster? There is already a Pro-Circuit pipe on it.
Thanks for any help guys, I am really looking forward to riding this year. The weather up here is starting to look promising!
Corey
