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big bore kit-pros and cons.

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thinking of adding athena 280cc kit to 06' crf250R. I race harescrambles and ride tight eastern style woods. pro's to this kit are: better low end, longer valve life, and more mid. Anyone have any more or any possible negatives? Bike needs more punch but I don't want a 450(been there and done that).:ride:

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the negitives are that the piston will have to be replaced more frequently than stock, I have read about some one having to replace their piston 3 times in 120 hours. And the bottom end will not last as long, it will have to be replaced more often (crank and rod)., you will not be able to revv out the same amount as without the big bore...

The pros.

More power, slightly longer valve life because you are not revving out as much as without the kit

Fore me what I would do if you want more power, Install a high compression piston 13.5:1, install a full race RHC cylinder head (ported polished, his valves, and his cam), install an aftermarket exhaust system (White bros aluminum pro or Procircuit Ti-4), and jet the bike properly. with this setup you should be able to get over 40 horsepower... Probablly not far off what you would get with the big bore.

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Listen to Honda, he knows what he is talking about. I agree with him and if i wanted added power out of my 07, i would go with jetting, exhaust and some head work to get the power instead of putting in a BB Kit. Some of my Yami friends have BB Kits on their bikes and it is true that the valves do last longer, but the piston takes a big hit and my friends are checkin their pistons and rings after about 20-30 hours of good riding

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One big pro ...... listen to the stuff they're talkin about. It's expensive ....BB is $600... a bit cheaper than a 600 dollar head from RHC 800 for a pipe, and 150 for hi-comp piston

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Huh? I disagree with the thought that you have to replace the pistons and bottom ends on a big bore kit more often. I've got over 50 hrs on mine with zero problems. Others I know have experienced the same thing. The only draw back it the bike doesn't rev as high. But, a good cam helps that.

If you want more power - lots more- it's the way to go!

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Huh? I disagree with the thought that you have to replace the pistons and bottom ends on a big bore kit more often. I've got over 50 hrs on mine with zero problems. Others I know have experienced the same thing. The only draw back it the bike doesn't rev as high. But, a good cam helps that.

If you want more power - lots more- it's the way to go!

I agree. The big bore piston will last longer than a OEM one because you're not revving it as high.

Personally, I didn't like the 270 kit because it didn't rev fast enough for me.

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sounds like a hassle either way I go. Too bad the manufacturers don't make a 300cc or something similar. Maybe I should have kept my 250 2-smoker!:ride:

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by the way, has anyone ridden a 250f with the big bore kit in the woods? how is it? The only moto-x I get near is when it is included in a harescramble( I like it but there are NO tracks anywhere in my area so my bike is ridden only on tight trails.)

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how bout an exhaust and 13.5 piston. Relatively cheap if you buy exhaust from ebay (or mine). YOu could also get the crower regrind which is supposovely very good for bottom/mid. So thats about 350+ exhaust and you should have that extra grunt.

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I've already got the hi-comp. piston in, but I'm still running stock exhuast, the aftermarket twin pipes are too pricey. I'm wanting to add a rekluse to my bike and I know that will mellow it out a little bit more so I need to come up with a little more power. The 250f is a great bike, but maybe I just spent too much time on a 2-stroke.The bike is great but at times just seems a little underpowered in some situations.

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I have an 05 CRF250R with JE 13.5:1 hicomp piston, PC Ti-4 full exhaust system, new RHC ported head and valve train, Rekluse clutch and have done all the carb mods. I am 200lbs. and can't say that I have ever been in a situation where my bike didn't have enough power to do the job.

I believe that if you at the very least go with a quality aftermarket exhaust you will notice a huge difference in the power output of your bike.

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sounds like a hassle either way I go. Too bad the manufacturers don't make a 300cc or something similar. Maybe I should have kept my 250 2-smoker!:ride:

Now there you are wrong, MaxRPMS make a 315 kit for the crf 250r, it includes an aluminum cylinder, balanced crank, wiseco pro-lite piston and a lomger cam and chain guide...but two things- you have to machine your cases to install the crank and the package costs $2,835 USD:crazy:

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sorry to thread mine... but I think alot of guys in this thread that say "go hi comp" etc to boost low end dont realise that many woods riders don't always have access to the highest quality fuels when out riding in a remote location. 13.5 is starting to get pretty high for poor fuel.

I'd say the 13.1 athena piston is more than high enough as it is.

I've just ordered the athena kit... I've already got a hot cam, RHC 07 head etc but running a Q2 exhaust so not too worried about losing top end as i've already killed most of my over rev with the exhaust.

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i also have the athena kit and couldnt be happier. lots of riding time on it without a single problem. installed a stage 2 hot cam last week after a year on the big bore and the gained a good deal of mid and top end. big bores make great low end motors. for woods riding you should be able to put it in 2nd or third and leave it till you hit the next straight. i ride only mx and the thing reved so fast i was shifting too much. the new cam helped stretch each gear out a little further. my next buy is an exhaust system. looking for still more overev. if so its gonna be the perfect vet bike. this thing will rip you off the seat and is a blast to ride. i have to think this is easier on the motor than building a full tilt high revving high compression national type motor to get the same result. during the cam install my valves were still perfect and have not moved since i bought the bike in feb 06. you have to maintain these bikes like crazy. i could not imagine buying this bike when i was 15 yo. without a mechanic for a dad. most of us cut our teeth working on two smokes where a dumb mistake didnt cost two grand to fix.

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my dad has a crf/x with a thumper racing 280 kit, fmf powerbomb/q4, and a few other mods, when compared to my RHC crf/r it isnt as fast and makes a completely different power but is still a blast to ride and for about half the cost of my r! i think that the 280 would wake the r model up a little more than the x model as well and i would definatly recommend it to anyone :thumbsup:

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as a vet rider i considered the big bore,but generaly liked the nature of the stock crf250r power.as far as valves lasting longer w/ big bore i dont think that would have worked with me,i'm a definate 125 type rever.went with FMF 4.1 ti dual megabomb sys. first-power improved everywhere,next pro circiut piston-even more bottom&top,not to mention the trivial mods done before those two i am very happy with the results on my 06crf250r.btw last bike 05 yz250,not that type of power,but effective and good for me,cam next.order of mods must be considered,unfortunatly for the price,but if you don't get a pipe don't get anything.

248'sdad#87

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