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330+ cc cheater bike.

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i was contemplating my big bore options for my 84 cr250 and though of the aftermarket cylinders for atc and trx 250r's. i did a little measuring and found that they will bolt directly on. for some of the bigger cylinders you will have to bore out the hole in your cases to get the cylinder to fit but that's a piece of cake.

this would give you enough power to walk most 450's and 500's but i don't know how rideable it would be on the track. some of the smaller cylinders in the 330cc range would probably give you a nice manageable power band. they have a few different models with i assume different port layouts, in a bunch of different bore sizes.

my cylinder is trashed, this may be the perfect option for me.

http://www.cpindinc.com/pub/part_list?manufacturer=2

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better do alittle more homework. the cpi cylinders are using a 130 rod, you have 125mm. im sure you can make all the pieces fit together but it might take some mix and match. spacer plate ? new intake and reeds ? not sure but i think they use cr500 reed setup, could be wrong though. pipe ? and even if the studs are the same how good will the cylinder/case surface match up at the ports ? airboot junction probly wont match right up. new head stay ?

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I put a 330 cylinder on my "01" CR 250. Ran real well. Geared it 14/49. Wish i still had it. Those cylinders from ESR 250 will fit some of the new models RM, YZ, etc.

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better do alittle more homework. the cpi cylinders are using a 130 rod, you have 125mm. im sure you can make all the pieces fit together but it might take some mix and match. spacer plate ? new intake and reeds ? not sure but i think they use cr500 reed setup, could be wrong though. pipe ? and even if the studs are the same how good will the cylinder/case surface match up at the ports ? airboot junction probly wont match right up. new head stay ?

changing the rod length is no problem, especially if i was going to stroke it anyway. the rest of the things you mentioned are non-issues, the cr and trx cylinders are interchangeable.

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I put a 330 cylinder on my "01" CR 250. Ran real well. Geared it 14/49. Wish i still had it. Those cylinders from ESR 250 will fit some of the new models RM, YZ, etc.

which cylinder did you use on the 01?

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changing the rod length is no problem, especially if i was going to stroke it anyway. the rest of the things you mentioned are non-issues, the cr and trx cylinders are interchangeable.

i don't want someone reading this to get the wrong information, what i meant to say is that the trx250 and 1984 model cr250 cylinders are interchangeable, i do not know about the later year model cr's.

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damn that esr cylinder looks nice. and pretty cheap too compared to the cp ind. stuff.

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at what point dose reliability become an issue .. a 250 bored to a 330 ?

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at what point dose reliability become an issue .. a 250 bored to a 330 ?

I used to race a TRX250R with an ESR 310 powervalve cylinder - It was super reliable.

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none of it is a issue if you have the money and knowledge.

years ago i was going to put a cpi 500cc cylinder on a cr250. never did get around to it but it seems i came to the conclusion '84-'86 cases would work. starting in '87 i think theres a boost port thing in the center of the cases, thats one problem and there may be others as well.

assuming my hunch was right and the '85-86 cases will work, i would still like to do that project if i ever got the money. still to this day ive never seen or heard of it being done. been a while but its seems like i figured it would be fairly easy to do, not sure why no one else has done it.

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Derek at hp bikes is working on a 350cc cylinder kit for cr's and yz's.Can't wait until it's available.

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I have an 88 trx330 dune quad. It has a custom ported ESR 330 cylinder and makes 65hp on a dyno at the wheels on a reliable setup. It walks away from any 450/ ktm 540 etc in the sand. Id imagine itd be pretty killer in a bike. Mines a non powervalve setup so it hits pretty hard, but still has lots of lowend. But ESR makes a mechanical powervalve cylinder too if you want a little smoother powerband:thumbsup:

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