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View Full Version : anyone bore out a 300EX?



not2hi
06-24-2002, 08:08 AM
i have a 98 300EX thats smokin, i'm guessing either cylinder walls are scratched or the rings are gone. It has a Wiseco stock bore piston. Can the stock 300EX head be bored or is there a sleeve in there?

I'm hoping i can either just hone it and replace the rings with the next size up, worst case is a new one-size-up piston and rings.

wait, can you even get oversize rings for a stock size wiseco piston?

Any advice from someone who's done this is appreciated!

rbm300ex
06-24-2002, 08:38 AM
I have a 2000 300ex that smoked bad when I bought it. I bored it out .80 over, new Wiseco piston and White Bros. all-around cam cause the orig. cam was scrap once I got into it. I don't think the previous owner EVER changed the oil or filter, just kept adding when needed. I might not have needed to bore it out and could have just done rings, but if you have it all apart, why not make it better! The piston kits cost the same and a cyl. bore is only $30.00 or so. I also had the head ported while it was apart, that cost about $130.00 but I was told by several and had also read in these forums that a 300ex can benefit well from a porting job. I am pleased with the outcome, it really woke her up.
I'm gonna get an oil cooler from FST for it also. Other than the machine work, I did it all myself, not difficult, get a Clymer manual and search these forums for old info.
To answer your orig. ?, yes there is a steel sleeve in the cyl. and you can bore it out one more time over .80 before you need to press out the old sleeve and put in a bigger one (like the 330's).
.80 over bore brings it as close to 300cc as you can get.
Hope this helps ya a little, I know when I was searching this stuff out a few months ago, I too, was hungery for info. from folks who had done it.
Randy

06-24-2002, 07:42 PM
It is probably ready for a bore job. You should only bore it .020 over and get a piston and rings that size. That way you can bore it again someday. If you bore it .080 it will run hotter and you will need a new sleeve the next time. The extra discplacement would not be noticeable.Like rbm said, get a Clymer manual and you can do a lot of the work yourself. Good luck.