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Hello everyone, new member here.

I recently picked up a unknown to me roached CRF250R. Its an 04.

After the first oil change it was indicated it would need a rebuild. So I've been doing the process myself.

Last night I split the cases and got everything apart. Only to find this engine has had a crank detonation previously, and the rebuilder chose to repair the case halves using JB weld on the case halves where the crank would be. Case half walls are all scored and toast.

But I've found the right side case half for an 04 is no longer made by Honda.
Case halves for an 05 are still made though. And it seems to me that these engines from 04-07/09 went through very little changes.

So, ultimately I'm wondering if I can rebuild this engine with 05 case halves but 04 internals such as transmission gears and etc.

Any help is greatly appreciated.

Welcome to the site !!

From what I found , the left is the same part # , but the right is different , not sure what the difference is , but it seems the left is interchangeable , but either the right is not , or there is a difference between the 2 that may be physical internally or externally , and not sure what that could present as far as issues go , what I would say is if you can't locate a 04 right case on EBay , then I would get a 05 and just check with the Service Manual on specs as far as crank , and tranny shafts endplay shims , etc. , and try to get the shims to work , as you may have to add , swap around or remove shims to make it work , but the engine internal parts all seem to be the same for 04-05 , or even 04-09 , so I do not see a issue with the internal parts working , and as long as the 2 case halves match ,then you should be fine with the rest of the parts ... the only other possible difference may be engine mounts or the spacers for them if used ...

Hope that helps ..

This is my source : http://www.oem-cycle.com/HONDACRF450RBIKEID.shtml

The other thing that can be different is the hole for the rear swingarm pivot.
Just something to check.

Welcome to the site !!

From what I found , the left is the same part # , but the right is different , not sure what the difference is , but it seems the left is interchangeable , but either the right is not , or there is a difference between the 2 that may be physical internally or externally , and not sure what that could present as far as issues go , what I would say is if you can't locate a 04 right case on EBay , then I would get a 05 and just check with the Service Manual on specs as far as crank , and tranny shafts endplay shims , etc. , and try to get the shims to work , as you may have to add , swap around or remove shims to make it work , but the engine internal parts all seem to be the same for 04-05 , or even 04-09 , so I do not see a issue with the internal parts working , and as long as the 2 case halves match ,then you should be fine with the rest of the parts ... the only other possible difference may be engine mounts or the spacers for them if used ...

Hope that helps ..

This is my source : http://www.oem-cycle.com/HONDACRF450RBIKEID.shtml

That is a wonderful list! From what I can tell from comparing part # fiche's is the transmission countershafts are different, as in different part #'s. But the transmission gears are the same across the 04-05 year.

If need be I wonder if I can get an 05 case and a part out 05 transmission.

And the swing arm bolt is the same across the 04-05 year.

Yea , I wish the list was more complete , but I believe it was compiled by different people , and most likely people like you that have tried to use a part for one year in another .... however , a lot of the parts carry the same or a superseded part number to another year , so that helps when Honda keeps the same component year after year ....

I ran into issues like with your 04 , with my 02 450R , it is kind of a one off bike , only select parts swap , others just simply are different , but I was able to use 02-04 parts , but some were 02 only or 02-03 , since that bike is now real old , is finally why I got rid of it and got my 20 ... it was just getting to the point of how much are you going to stick into a 18+ year old bike , and clean non worn out parts were almost non existent , so I opted for newer tech , and I am so glad I made the change .. this bike is so superior in almost every way from even a 5 year old design ... I would never go back to old , at least for a track bike ... my trail bike is a almost stock 06 450X and I love that bike as well ... and parts for it are pretty much the same with very few exceptions up till 17