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02 cr250 complete engine rebuild time... need game plan

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I have a 2002 cr250 and over the weekend the engine quit. My good friend was riding it right behind me and the engine started making a loud rattling noise and less than 2 seconds later it locked up. I just assumed he was riding 2 gears too high for the trail we were on so I tried to kick it over and it would fire and immediately stop... I left him there with it for 1 1/2 hrs while I squeezed a truck down the trail to pick it up.

Fast forward to today, I pulled the cylinder off to have a look and it wasn't pretty, the top of the piston had significant damage along with the dome of the head and the rings have a few dings in them (but still are able to move in their grooves) and the cylinder does not look to be scratched but the powervalves have some deep knicks in them. The bottom end is pretty well locked up both at the crank bearings and big/little end rod bearings. I can get them to rotate using substantial force, but they are far from doing so freely. The crank bearings and wrist pin bearing along with piston/rings were all replaced earlier this year and all appear to still be intact which leads me to believe I had a big end bearing come apart and scatter the pieces everywhere else.

I have the engine out of the bike now and will start full disassembly as soon as I tidy up my work bench (probably tomorrow), so I need to figure out a game plan by the end of the week. This bike is used primarily for my tougher trail rides as well as the occasional desert jaunt if that plays into the rebuild equation other than port work.

I had been planning on sending my cylinder out for port work anyway, so now is the time. I had originally been planning on sending it to Eric Gorr, but ESR is only 15 minutes away from me, does anyone have experience with 02+ cr250's and Eddie Sanders Racing? If the cylinder needs replating (I really hope that it doesn't) I am considering going with a 265cc setup... ONLY IF IT NEEDS REPLATING. I will most likely be replacing the piston and rings with a Wiseco unless someone can talk me out of using a forged piston.

My other question is in regards to the crank itself, is there any benefit in having my crank rebuilt (by whichever shop does my port work) as apposed to just purchasing a new complete crank from hotrods or Wiseco? I've used hotrods complete cranks on other bikes and not had any complaints and the price to have mine rebuilt is almost exactly the same price as buying a new one (the wiseco crank is ~$50 cheaper.)

Edited by TheLetterJ

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I had ESR do a custom long rod stroker crank for me and they did a great job and were easy to deal with. Not sure what their porting is like but overall i'd recommend them

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I had thye same issue with my 02 CR 250. The lower con rod bearing took a crap and locked the motor up. Would start for a split second, then die. I sent my OEM crank to Cooksey cranks in Texas for a rebuild with a Pro-X con rod kit. Total cost was around $175 shipped. The problem with buying a new crank, is that the new one might be slightly out of spec and would need to be sent to a pro (Cooksey) for trueing anyways. When it comes to motor work, I try to stick with OEM stuff. I have not heard many good things about the Wiseco cranks regarding quality control.

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Recently did a full rebuild on a 03cr250r. I would highly recommend the wiseco piston, but don't forget to drill the exhaust bridge cooling holes per the included instruction sheet.

Everything else I would go oem. Crank, bearings,gaskets, hondas stuff is the best out there. Also measure shifter forks while you're in there, and inspect trans bearings. I did a full set of bearings but most weren't needed.

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I second OEM. I will no longer run forged pistons in a 2 stroke unless the bore is wore large. Replated cylinder with cast piston = quite smoooth engine with no piston scuff.👍

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Im also interested in the responses regarding to port work. There is quite a few options, I was contemplating either Pro Circuit or Eric Gorr. Im just scared to have it done from pc and its an all top end beast. What are you looking to improve, over rev, low to mid?

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Ideally I'd like to improve low end through midrange power without a noticeable sacrifice in top end. Most of my riding on this bike (~70%) is tight single track or no higher than 3rd gear stuff. The only reason that I don't want to lose any top end power is that I will use this bike in the desert/dunes a couple times a year, but realistically my big thumper serves that purpose better anyway.

When tuners say that their low/mid port job has a "flat" top end, does that mean that it doesn't have as much HP, or will it not even be able to rev as high as it use to? I can deal with less topend HP, but I would prefer that it could still spin up as high, the 2t is already at a disadvantage to a modern 4t when it comes to peak rpm's.

Does a low/mid port job still have the typical 2t hit just at an earlier rpm, or is it typically just smoother power down low? I wouldn't mind "dumbing" down the hit, but I really can't decide between a setup like EG's "mo-betta" (Mo-Betta: a wider smoother powerband with less hit in the mid-range) vs low/mid port job... Is a FWW going to be the answer?

Who has a low/mid port job on their bike that could share some insight?

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Ideally I'd like to improve low end through midrange power without a noticeable sacrifice in top end. Most of my riding on this bike (~70%) is tight single track or no higher than 3rd gear stuff. The only reason that I don't want to lose any top end power is that I will use this bike in the desert/dunes a couple times a year, but realistically my big thumper serves that purpose better anyway.

When tuners say that their low/mid port job has a "flat" top end, does that mean that it doesn't have as much HP, or will it not even be able to rev as high as it use to? I can deal with less topend HP, but I would prefer that it could still spin up as high, the 2t is already at a disadvantage to a modern 4t when it comes to peak rpm's.

Does a low/mid port job still have the typical 2t hit just at an earlier rpm, or is it typically just smoother power down low? I wouldn't mind "dumbing" down the hit, but I really can't decide between a setup like EG's "mo-betta" (Mo-Betta: a wider smoother powerband with less hit in the mid-range) vs low/mid port job... Is a FWW going to be the answer?

Who has a low/mid port job on their bike that could share some insight?

Disclaimer: My opinion is not based on the power curve of a 250.

I had EG do a low mid port on my 2001 cr80 that we bored to a 105. It has a ton of low end torque, best small bore 2 stroke I have ever ridden as far as low end torque. It feels just as strong on the top end as the 80 did. Unfortunately, I couldn't tell you if a low mid port is going to cause a power loss on your top end because we also got the bb kit on the 80 but I love the low/mid port for the 80, made it an awesome bike.

I did the "mo betta" port on my 125/144 bb conversion, also done by EG. I like that port job but have considered sending it to him to get the low/mid port since it does lack for low end (typical for a 125). Anyway, IMO, I would probably get the mo betta port from EG if I were doing a 250 since they have way more low end torque then a 125 from the factory. FWW won't do anything except make your power curve more tractable, doesn't add low end anything.

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To be honest with, I noticed much better low to mid range power just by installing the pwk carb, thats a must do, not sure if youve done it yet but that would be my first mod.

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