Modernizing/ rebuilding a 2002 CR250R

DanCaughell331
Edited Date/Time 5/11/2015 11:54am
I'm in the rebuilding process of a 2002 cr250 and turning it into the modern day two stroke I've always wanted! I bought the bike for 2,000 from a local guy because I wanted a project bike that I could build exactly how I wanted, and I wanted to get away from the four strokes like I've owned before. Below is how it looked when I bought it and how it looks now. Just freshened up with plastics, graphics, seat cover, bars, and a new clutch perch. I will post more build progress pics as it unfolds! Thanks for looking.

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DanCaughell331 12/21/2014 11:15am
12/21/2014 11:15am
Here's some photos from last weekend starting the tear down process.






I'm going to pull the motor out of the frame today, along with everything else on it so I can start cleanup. Once it's pulled apart I'll put up some pictures of close up more detailed shots. In the mean time, here's what I have so far for parts! Not much, but I just started those whole project a week ago so I'm not doin too bad.

Pro circuit works pipe and 304 silencer,as well as a new exhaust flange.

A new boyesen Rad Valve.


southwick_mx 12/21/2014 12:36pm
12/21/2014 12:36pm
This'll be nice to follow! Now pull all the stops and make this your dream bike!
DanCaughell331 12/21/2014 1:13pm
12/21/2014 1:13pm
southwick_mx wrote:
This'll be nice to follow! Now pull all the stops and make this your dream bike!
That's the current plan! Obviously money is the biggest factor in anything when it comes to bike builds but I believe I can get it very close to what I want by the end of winter. I'm going for that real trick works bike look of the early 2000's, just with a more modern twist to it. Thanks for following!

The Shop

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DanCaughell331 12/21/2014 4:36pm
12/21/2014 4:36pm
Well after a couple of hours screwing around in the garage, I finally got the motor out of the frame and on the workbench.



And as you can see, she needs a whole lot of TLC. Give me a couple months and it'll look a hell of a lot better!







rmartin517
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rmartin517 12/21/2014 6:27pm
12/21/2014 6:27pm Edited Date/Time 12/21/2014 6:31pm
bot trying to pick at your build. The Boyesen exaust flange is better than the PC on. It is actually cut to match the D shaped port. I did everything you are doing to an 03 a while back. The biggest changing bolt on part was the kehin airstriker from JD. Honestly I don't think anything else made much of a difference except for the PC pipe and carb. It was a fun build. highly recommend going with and 05 bad gasket or having the base cut and the motor ported or you will not gain much power out of the bike. Enjoy the build i has tons of fun with mine. Looks like you are making good progress. They handle so good.
DanCaughell331 12/21/2014 8:49pm
12/21/2014 8:49pm
rmartin517 wrote:
bot trying to pick at your build. The Boyesen exaust flange is better than the PC on. It is actually cut to match the D shaped...
bot trying to pick at your build. The Boyesen exaust flange is better than the PC on. It is actually cut to match the D shaped port. I did everything you are doing to an 03 a while back. The biggest changing bolt on part was the kehin airstriker from JD. Honestly I don't think anything else made much of a difference except for the PC pipe and carb. It was a fun build. highly recommend going with and 05 bad gasket or having the base cut and the motor ported or you will not gain much power out of the bike. Enjoy the build i has tons of fun with mine. Looks like you are making good progress. They handle so good.
rmartin517 hey man I appreciate the input! I just started the build and I'm already pretty deep into it. You recommend an 05 head? I wasn't sure if that's what you were saying. I already decided long ago that a keihin carb was definitely a must for this bike since the mikuni is a garbage carb. I'm trying to keep it so I have power throughout the RPM range because I do a multitude of riding aspects, trails every once in awhile. Who would you recommend for porting? I talked to pro circuit and they gave me prices on everything just not sure how much really needs to be done to one of these cylinders to make it crisp.
Cmiller493
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Cmiller493 12/21/2014 10:26pm
12/21/2014 10:26pm
05 head gasket, Kehin AS, some 50/50 mix of race and pump gas, and you will be good to go!
DanCaughell331 12/22/2014 5:22am
12/22/2014 5:22am
Cmiller493 wrote:
05 head gasket, Kehin AS, some 50/50 mix of race and pump gas, and you will be good to go!
Cmiller493 your Cr is bangin! Great lookin bike. Why the 05 head gasket, just smaller compressed thickness than an 02 gasket? Also what does that do with the squish band/ does it throw anything off in the motor?
Cmiller493
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Cmiller493 12/22/2014 6:31am
12/22/2014 6:31am
Thanks man I appreciate it! The gasket is .010" thinner so it will lower the cylinder for more compression and bring the squish to around .050" which is what you would want to see. It doesn't throw anything off in the motor just gives it more bottom end which is what the cr is lacking. I would also invest in an MX Bonz air box seal kit if you haven't already those air boxes don't seal very well.
cslacker
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cslacker 12/22/2014 7:02am
12/22/2014 7:02am
It's the '05 base gasket you would want, not head gasket. It is only about .008" difference so you won't notice much if any difference, at least I didn't. Don't worry about the Boyesen exhaust flange over the PC as the '04 is the only D shaped exhaust port I have ever seen on a CR. My 03 and my friends 02 both have round exhaust ports and the PC flange matches it perfectly. The PWK is a great upgrade but you will get the best results from porting. I used Eric Gorr for mine and love the way it pulls, really smooth from idle to overrev.
DanCaughell331 12/22/2014 7:18am
12/22/2014 7:18am
cslacker wrote:
It's the '05 base gasket you would want, not head gasket. It is only about .008" difference so you won't notice much if any difference, at...
It's the '05 base gasket you would want, not head gasket. It is only about .008" difference so you won't notice much if any difference, at least I didn't. Don't worry about the Boyesen exhaust flange over the PC as the '04 is the only D shaped exhaust port I have ever seen on a CR. My 03 and my friends 02 both have round exhaust ports and the PC flange matches it perfectly. The PWK is a great upgrade but you will get the best results from porting. I used Eric Gorr for mine and love the way it pulls, really smooth from idle to overrev.
i can see the base gasket dropping the whole cylinder and head to increase compression but not change squish, where the head gasket would change squish since it would move the head up or down. how much does the porting from Eric Gorr cost? (in most situations)? and is he just porting the transfer ports coming into the cylinder, or is that matching up the bottom of the ports to the crankcase? i know on the old school TRX and ATC 250r motors the hot thing to do was make crankcase stuffers to lower the volume of the crankcase which gave them more bottom end. not sure if that's a prevalent modification on the CR's, i've never screwed around on one of these motors with the electronic powervalve. i'm not looking for a all out track motor, as i do alot of riding whether its sand dunes, tracks, or some trail riding. i just want to get rid of the doggy bottom end and poor jetting issues. essentially just a good crisp 2 stroke like the YZs and so on. any help would be greatly appreciated!!
cslacker
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cslacker 12/22/2014 7:36am
12/22/2014 7:36am Edited Date/Time 12/22/2014 8:08am
DanCaughell331 wrote:
i can see the base gasket dropping the whole cylinder and head to increase compression but not change squish, where the head gasket would change squish...
i can see the base gasket dropping the whole cylinder and head to increase compression but not change squish, where the head gasket would change squish since it would move the head up or down. how much does the porting from Eric Gorr cost? (in most situations)? and is he just porting the transfer ports coming into the cylinder, or is that matching up the bottom of the ports to the crankcase? i know on the old school TRX and ATC 250r motors the hot thing to do was make crankcase stuffers to lower the volume of the crankcase which gave them more bottom end. not sure if that's a prevalent modification on the CR's, i've never screwed around on one of these motors with the electronic powervalve. i'm not looking for a all out track motor, as i do alot of riding whether its sand dunes, tracks, or some trail riding. i just want to get rid of the doggy bottom end and poor jetting issues. essentially just a good crisp 2 stroke like the YZs and so on. any help would be greatly appreciated!!
A thinner base gasket (05-07) will change the squish since it drops the whole thing. Im pretty sure whoever was saying to use the 05 head gasket mistyped as they are the same thickness and would not change anything. If you are getting porting done don't bother with running different gaskets as they should fix your squish and set you compression to your choice of fuels when they are doing it.

Based on what you are looking for Eric Gorr has his "Mo Betta" porting. It will wake up the bottom end a bit, especially with the pwk swap, but it will also keep the powerband smooth and broad with a good overrev.
Matt Fisher
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Matt Fisher 12/22/2014 7:54am
12/22/2014 7:54am
The 05+ gasket is different than the 02-04 base gasket. It's metal and thinner than the earlier model's paper type gasket.
In my experience (03 CR250), it does make a noticeable difference.
cslacker
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cslacker 12/22/2014 8:07am
12/22/2014 8:07am
Matt Fisher wrote:
The 05+ gasket is different than the 02-04 base gasket. It's metal and thinner than the earlier model's paper type gasket. In my experience (03 CR250)...
The 05+ gasket is different than the 02-04 base gasket. It's metal and thinner than the earlier model's paper type gasket.
In my experience (03 CR250), it does make a noticeable difference.
I know the 02-04 base gasket is .008" thicker than 05-07 base gasket. What I said above was that it is not the HEAD gasket as some were saying previously. I personally noticed zero difference when I did the swap. And like I mentioned before, if he is getting porting done anyways there is no reason to do the base gasket swap as the guy doing the engine work will be doing the port heights etc based on a stock 02 base gasket. Then it gives you the option to play around at a later date.
DanCaughell331 12/22/2014 8:18am
12/22/2014 8:18am
Matt Fisher wrote:
The 05+ gasket is different than the 02-04 base gasket. It's metal and thinner than the earlier model's paper type gasket. In my experience (03 CR250)...
The 05+ gasket is different than the 02-04 base gasket. It's metal and thinner than the earlier model's paper type gasket.
In my experience (03 CR250), it does make a noticeable difference.
i appreciate the input! hell, i appreciate all the comments you guys have put up so far. it's good to have some first hand advice from people who have done these builds before, it gives me a basis to do some more research and whittle down my results to get the best combination suited for me and my riding style.
DanCaughell331 12/22/2014 8:27am
12/22/2014 8:27am
Cmiller493 wrote:
Thanks man I appreciate it! The gasket is .010" thinner so it will lower the cylinder for more compression and bring the squish to around .050"...
Thanks man I appreciate it! The gasket is .010" thinner so it will lower the cylinder for more compression and bring the squish to around .050" which is what you would want to see. It doesn't throw anything off in the motor just gives it more bottom end which is what the cr is lacking. I would also invest in an MX Bonz air box seal kit if you haven't already those air boxes don't seal very well.
is that the current motor setup in your CR? with the 05 head gasket and all that i mean. i'd like to still be able to run pump fuel, but i'm not necessarily opposed to running a 50/50 blend of VP or Sunoco 110 octane with non ethanol premium. just because of the characteristics of race fuel being more predictable than pump fuel. as far as porting the cyclinder did you do anything there? i already know i'm buying a brand new cyclinder because my powervalve is clapped out, the coating is starting to go away, and it's way out of tolerance so theres no point in me going throught the hassle to rebuild the jug when i can buy a new one for the same price. im 180 LBS so i'm not the lightest, but not the heaviest. i need power that will actually pull me through without having to destroy the clutch and ride it at 8,000 rpm everywhere i go. not looking for a tractor motor, but fixing the weak bottom end while adding power everywhere else.

Pit Row

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DanCaughell331 12/22/2014 8:33am
12/22/2014 8:33am
Matt Fisher wrote:
The 05+ gasket is different than the 02-04 base gasket. It's metal and thinner than the earlier model's paper type gasket. In my experience (03 CR250)...
The 05+ gasket is different than the 02-04 base gasket. It's metal and thinner than the earlier model's paper type gasket.
In my experience (03 CR250), it does make a noticeable difference.
cslacker wrote:
I know the 02-04 base gasket is .008" thicker than 05-07 base gasket. What I said above was that it is not the HEAD gasket as...
I know the 02-04 base gasket is .008" thicker than 05-07 base gasket. What I said above was that it is not the HEAD gasket as some were saying previously. I personally noticed zero difference when I did the swap. And like I mentioned before, if he is getting porting done anyways there is no reason to do the base gasket swap as the guy doing the engine work will be doing the port heights etc based on a stock 02 base gasket. Then it gives you the option to play around at a later date.
Matt i'm not sure just yet whether or not the porting is a route i'm going to take. more so later next year or next winter might be a good time to do that for me, i may just put the motor together fresh this winter then ride it next season so i can really get a grasp for the power that one of these bikes make when it's rebuilt well and has good components on it, then go from there with a better idea of what i need from the bike. (also money is another issue in such tight time constraints getting this ready for april-may 2015 time frame)
cslacker
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cslacker 12/22/2014 8:36am
12/22/2014 8:36am
DanCaughell331 wrote:
is that the current motor setup in your CR? with the 05 head gasket and all that i mean. i'd like to still be able to...
is that the current motor setup in your CR? with the 05 head gasket and all that i mean. i'd like to still be able to run pump fuel, but i'm not necessarily opposed to running a 50/50 blend of VP or Sunoco 110 octane with non ethanol premium. just because of the characteristics of race fuel being more predictable than pump fuel. as far as porting the cyclinder did you do anything there? i already know i'm buying a brand new cyclinder because my powervalve is clapped out, the coating is starting to go away, and it's way out of tolerance so theres no point in me going throught the hassle to rebuild the jug when i can buy a new one for the same price. im 180 LBS so i'm not the lightest, but not the heaviest. i need power that will actually pull me through without having to destroy the clutch and ride it at 8,000 rpm everywhere i go. not looking for a tractor motor, but fixing the weak bottom end while adding power everywhere else.
If you are planning on buying a new jug, powervalves etc... go with an 03. It has better stock porting and according to most tuners is the best to work with when porting.
DanCaughell331 12/22/2014 9:05am
12/22/2014 9:05am
cslacker wrote:
If you are planning on buying a new jug, powervalves etc... go with an 03. It has better stock porting and according to most tuners is...
If you are planning on buying a new jug, powervalves etc... go with an 03. It has better stock porting and according to most tuners is the best to work with when porting.
I already have my pipe/silencer/ exhaust flange for an 02....will it fit the 03 jug just the same? because i have seen different pipes and flanges between the years as far as what is listed by different companies for example instead of (hypothetically) "02-04" or "02-03" model years they are separated
cslacker
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cslacker 12/22/2014 9:58am
12/22/2014 9:58am
Not positive. I do know that fmf/pc have the 02 listed as a different pipe than the 03-04. Not a huge deal anyways if you just go with the 02 jug. A good tuner will get you great results from it.
rmartin517
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rmartin517 12/22/2014 2:22pm
12/22/2014 2:22pm Edited Date/Time 12/22/2014 2:29pm
rmartin517 wrote:
bot trying to pick at your build. The Boyesen exaust flange is better than the PC on. It is actually cut to match the D shaped...
bot trying to pick at your build. The Boyesen exaust flange is better than the PC on. It is actually cut to match the D shaped port. I did everything you are doing to an 03 a while back. The biggest changing bolt on part was the kehin airstriker from JD. Honestly I don't think anything else made much of a difference except for the PC pipe and carb. It was a fun build. highly recommend going with and 05 bad gasket or having the base cut and the motor ported or you will not gain much power out of the bike. Enjoy the build i has tons of fun with mine. Looks like you are making good progress. They handle so good.
DanCaughell331 wrote:
rmartin517 hey man I appreciate the input! I just started the build and I'm already pretty deep into it. You recommend an 05 head? I wasn't...
rmartin517 hey man I appreciate the input! I just started the build and I'm already pretty deep into it. You recommend an 05 head? I wasn't sure if that's what you were saying. I already decided long ago that a keihin carb was definitely a must for this bike since the mikuni is a garbage carb. I'm trying to keep it so I have power throughout the RPM range because I do a multitude of riding aspects, trails every once in awhile. Who would you recommend for porting? I talked to pro circuit and they gave me prices on everything just not sure how much really needs to be done to one of these cylinders to make it crisp.
05 base gasket sorry. Cell phones suck on forums. Had a lot of fun with mine. Here is the link there is a place on my build to get some good carbon fiber parts.

http://www.vitalmx.com/forums/Moto-Related,20/My-2003-cr-250-2-stroke,1…
DanCaughell331 12/23/2014 8:57am
12/23/2014 8:57am
rmartin517 wrote:
05 base gasket sorry. Cell phones suck on forums. Had a lot of fun with mine. Here is the link there is a place on my...
05 base gasket sorry. Cell phones suck on forums. Had a lot of fun with mine. Here is the link there is a place on my build to get some good carbon fiber parts.

http://www.vitalmx.com/forums/Moto-Related,20/My-2003-cr-250-2-stroke,1…
haha i hear ya there. yeah i'm starting to notice a trend of the 05+ base gasket to drop the cylinder. any ideas as to how much that will actually bump compression and/or change the fuel type i'll need to run? like i stated earlier in the thread i'm not opposed to running 50/50 race fuel, but if i don't need to i would rather stay with non-ethanol premium and maybe a gallon of race fuel mixed in to keep things crisp. and thanks for the link to the carbon fiber parts, i like that rear caliper guard and those fork gaurds, but i may stay plastic on the front.
CamP
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CamP 12/23/2014 9:08am
12/23/2014 9:08am
If you have easy access to 100LL avgas, I'd recommend sending the cylinder and head to Gorr and have him work them for that fuel. It's cheap leaded fuel that's 100 octane. Bought some last week here in DFW for $4.40/gal.
DanCaughell331 12/23/2014 1:21pm
12/23/2014 1:21pm
CamP wrote:
If you have easy access to 100LL avgas, I'd recommend sending the cylinder and head to Gorr and have him work them for that fuel. It's...
If you have easy access to 100LL avgas, I'd recommend sending the cylinder and head to Gorr and have him work them for that fuel. It's cheap leaded fuel that's 100 octane. Bought some last week here in DFW for $4.40/gal.
Yeah I've heard of some people running avgas, my dad used to run it in his trx250r and loved it for the sake of cost efficiency. But unfortunately I'm not so sure how to get ahold of it out here in utah where I just got stationed. And I also ride st anthony sand dunes up in Idaho, and Oregon dunes where I'm originally from at least a couple times a year. So setting it up for pump or for race fuel just seems like a more accessible option. But I will definitely look into it considering the benefits versus cost! I appreciate it man.
Matt Fisher
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Matt Fisher 12/25/2014 10:24am
12/25/2014 10:24am
CamP wrote:
If you have easy access to 100LL avgas, I'd recommend sending the cylinder and head to Gorr and have him work them for that fuel. It's...
If you have easy access to 100LL avgas, I'd recommend sending the cylinder and head to Gorr and have him work them for that fuel. It's cheap leaded fuel that's 100 octane. Bought some last week here in DFW for $4.40/gal.
DanCaughell331 wrote:
Yeah I've heard of some people running avgas, my dad used to run it in his trx250r and loved it for the sake of cost efficiency...
Yeah I've heard of some people running avgas, my dad used to run it in his trx250r and loved it for the sake of cost efficiency. But unfortunately I'm not so sure how to get ahold of it out here in utah where I just got stationed. And I also ride st anthony sand dunes up in Idaho, and Oregon dunes where I'm originally from at least a couple times a year. So setting it up for pump or for race fuel just seems like a more accessible option. But I will definitely look into it considering the benefits versus cost! I appreciate it man.
Any local airport will have 100ll. Ogden or Morgan County should be nearby you. Great fuel for your CR.

The thinner base gasket will indeed raise the CR up a smidge which can increase the need for octane to stave off detonation. However, the thinner gasket also helps to correct the oversized squish area that Honda equipped the bike with from the factory. One of the benefits of a tighter squish is reduced tendency to detonate.

Yes, having the cylinder base turned and then having the head modified to match is a better choice, but for the $, can't beat the 05+ base gasket.
DanCaughell331 12/26/2014 11:55am
12/26/2014 11:55am
Matt Fisher wrote:
Any local airport will have 100ll. Ogden or Morgan County should be nearby you. Great fuel for your CR. The thinner base gasket will indeed raise...
Any local airport will have 100ll. Ogden or Morgan County should be nearby you. Great fuel for your CR.

The thinner base gasket will indeed raise the CR up a smidge which can increase the need for octane to stave off detonation. However, the thinner gasket also helps to correct the oversized squish area that Honda equipped the bike with from the factory. One of the benefits of a tighter squish is reduced tendency to detonate.

Yes, having the cylinder base turned and then having the head modified to match is a better choice, but for the $, can't beat the 05+ base gasket.
Sounds good Matt, I'll look into that option. And I'm sure if it's setup for avgas it won't hurt it to run race fuel if I'm riding somewhere that I don't have access to an airport readily available.
Matt Fisher
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Matt Fisher 12/27/2014 10:11am
12/27/2014 10:11am
100ll to race fuel should be pretty close unless the race fuel is oxygenated. That will throw everything off.
That said, airports are pretty easy to find.
DanCaughell331 1/19/2015 7:45am
1/19/2015 7:45am
Hey everyone sorry for the lack of posts! I've been super busy with work, I just got back from Sheppard AFB in Texas for some training. And I get surgery on the 21st so that'll put me out for about a month or so. BUT, today I'm going to clean up the frame and have it ready to go. So my question is....

What is the best aluminum cleaner y'all have used for this kind of application? I'm also going to be scuffing the frame down once it's cleaned to that works-bike dull kind of finish.

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