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Big Bore on 2006 yz250f?

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I asked this question a while back and didnt get a whole lot of response so Im going to ask once more! I have a bone stock 250f with a few top ends on it. I ll be doing it for the 3rd time here soon. Bike has roughly 130 hrs on it total. It still has the stock crank in it. Am I asking for trouble to throw a big bore on the stock crank? Im all about preventative maintenace on bikes but I also would feel completly comfortable doing a fresh top end stock bore on the stock crank. Its just that the fact that a 270 kit may be harder on the stock crank? Or is this being overly precatious? Id like to hear others thoughts. I never race I only ride for fun a few hrs on the weekends. Strickly mx Id say Im B level at my best and try to ride the bike fast but not beat on it. I do feather the clutch a bit but in all honestly that stock clutch is still holding up! Which makes me think in turn maybe Im worring to much and I dont ride it that hard lol. Valves are in spec as well. Its an 06 but I think it still has alot of life left.

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Mine is an 02 and it's on the 3rd top end; stock, 263, and now 300. No issues, no problems, just great power, torque, and reliability. With a big bore you typically rev the motor less so the longevity can even be greater. DO IT.

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If you dont race dont waste you money on a BB. I have an 08 yz250f stock I am 215 without gear and have no problems doing any jump on my track. most are 60-80 feet.also I have 129 hours still on stock piston and valves have not moved.Putting in new piston this winter. And the 06 is a great bike. I am also a B+ rider and do mainly MX.

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Far too many people have big-bore 250F's to be considered a waste of money. Having ridden stock displacement, and big-bore 250's I wouldn't consider owning a stock displacement 250F anymore. To each his own.

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Mine is an 02 and it's on the 3rd top end; stock, 263, and now 300. No issues, no problems, just great power, torque, and reliability. With a big bore you typically rev the motor less so the longevity can even be greater. DO IT.

now this is what I like to hear! I bought the 06 purely for reliability. I had an 01 250f as well. So I know the motor is strong I just wasnt sure if this was wise or not. Then again how much is +3mm. My buddy has the same thing and hes is going to do it. It will revive my passion to ride a little as well I think. Also the 130 hrs was not an estimate. I actually have an hour meter. I assume you also have an hr meter or are you just guessing?

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My first big-bore was only +2mm (263cc) and it made a BIG difference in power, much more than I thought it would. The +3mm (270) and +4mm (276) give more low-mid and about the same on top. I don't have an hour meter but I ride frequently and the rides are 60-80 miles long. I have built about a half dozen big-bore motors and have not had any problems.

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My first big-bore was only +2mm (263cc) and it made a BIG difference in power, much more than I thought it would. The +3mm (270) and +4mm (276) give more low-mid and about the same on top. I don't have an hour meter but I ride frequently and the rides are 60-80 miles long. I have built about a half dozen big-bore motors and have not had any problems.

...are you still riding the 02 then or was this on several different bikes? What other big bores have you done and on what types of bikes? Sounds like you have some knowledge in this area

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I have an hour meter since day one. I had a an ice cube Big bore on my 04 crf250 and was awesome very reliable. My 08 stock was faster and more power than my honda BB. Im not saying the BB is bad just a waste of money if your not racing.But to each his own,Good luck.

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Still on the 02. Bought it new, put a RPM's 263cc cylinder because I had a hard time riding with 250 2-strokes and bigger 4-strokes. Problem solved. Although it was plenty fast, I wanted a little more low end, bigger kits began to be available; 276, 290, 300. I went with the 300. Plenty of low end now, but it signs off earlier on the top end. Headwork is next on the menu to get the top end back. Don't miss it unless I ride in the desert.

I used to have a Kawasaki KLX-300, great bike but kinda slow. I put a Stroker 331 cylinder on, great power but the high compression made it real hard to kick over. After a while I put on a Thumper Racing 340 cylinder, 1mm bigger piston and much lower compression, similar power, a little less maybe, but much easier to kick over.

A friend of mine has a 1986 XR-250, he came off a 1985 XR-350 so he was missing the power, I put a 284 cylinder cylinder and had the head ported by XR's Only. Much, much, more power. He is totally happy.

I built a friends son's KX-80 to a 105. It rips.

I have a Yamaha Zuma, 50cc 2-stroke scooter, I put a 70cc cylinder on it, bored the carburetor 2mm, Boyesen reeds, Leo Vince pipe, Transmission mods...........

I have a bigger piston for my CR-500, haven't done it yet.

There were others over the last 20+ years.

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