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Bored to 340.. (250r question)
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Posted by: 300excrazy98

Hey guys, I am buying this 250r and the guy tells me that the cases were machined out by duncan racing for a 340 cylinder. my question is can you still run a stock cylinder? stock bore? or do you have to run the 340?

Posted by: nofearrider1

I dont know about the R but I like you sig, g unit haha

Posted by: 300excrazy98

ha thanks.. bump

Posted by: stocktires

Yes, a stock cylinder is fine. You just now have the option of running a 340. I can't remember all the details of case machining because it's been so long since I had my R

For some reason I want to think there's a negative side effect to having the cases machined.

Posted by: 300excrazy98

thanks

Posted by: trx250rkid

theres no negative side affect that i know of. you can run any cylinder you want.

Posted by: matt250r21

The only thing I can think of is a very slight loss of crankcase pressure.

Posted by: C-LEIGH RACING

Running a stock jug on cut out cases causes just a bit lower crankcase presure which will lower the top rev some but makes up for it with a bit better bottom end responce.
If your running a 38mm carb, you can over come the extra volume that the case cutting added by clamping on a 39/41.5mm carb, but then the power will be different, little sluggish on the bottom.
Neil

Posted by: Eddiesanders250

can you have the cases machined without splitting them?

Posted by: C-LEIGH RACING

quote:
Originally posted by Eddiesanders250
can you have the cases machined without splitting them?

No sir,

All the shavings & chips that the machining will produce from the cutting process will end up in the main & crank rod bearings, + the crank webs will be in the way of the machining tool bit.
Neil