2003 CR125 + 1998 CR125 engine?

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5/23/2015 6:29 PM

So basically I have 2 CR125s. I bought a 2002 CR125 for $1000 (pretty good deal in Australia) and it works 100%. Just really dirty and needed a suspension overhaul. But it worked and was 100% complete. Then I have my 1998 CR125 which was my first big bike after I stopped riding in my teens and it's a good bike, just stiff and looks dated, but the engine is pretty damn nice (I fully rebuilt it 10 hours ago, runs like a dream).

I know it was mostly the cylinder that changed over the years but I was wondering if it would be worth my while swapping the engines over? Is it a clean swap, or am I looking at just the cylinders (and I think the power valve rod thing)? I keep reading that the latter model CRs, specially the 125s were slow as balls.

Good idea to swap the '98 carb over as well?

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5/23/2015 6:47 PM
Edited Date/Time: 5/23/2015 6:47 PM

Not sure about the 98 carb, but this is what I did.

I started with a blown up 2002 and purchased a complete '92 top end. After doing a bottom end rebuild with the '92 powervalve actuator in place of my '02 it booted right up. I'm having issues now with exhaust fitment, mainly because I have an 05-07 pipe, and the old style cylinders hit the pipe.... but a ball peen hammer and a set of torches work wonders.

As for the carb.... If yours has the Mikuni throw it in the garbage. Get yourself a 38mm Keihin PWK Airstriker from JD Jetting.

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Washed up moto and enduro weekend warrior.

5/23/2015 6:48 PM

The motor bolt holes are a tad bit smaller that the the 02. You will need to ream them out. The cylinder swap is fairly easy just change the PV linkage. I have a 97 cylinder punched out to a 134 on my 02 and it rips.

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5/23/2015 7:19 PM

I built this 02 cr125 last winter. 02 bottom end, 95 cylinder, power valve governor and rod. The 95 cylinder i used is the same as your 98 engine.You will find the exhaust pipe angle different on the 98 cylinder. I used the 02 pipe sliced it almost through bolted the rear pipe hanger and tack welded the gap. Welded the pipe and it worked fine. Then counter sank the top power valve cover front bolts to clear the radiator hose. 02 intake and carb have fun!!!Photo


sliced pipe


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welded pipe
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power valve covers


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Photo

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5/23/2015 7:43 PM

MxKing809 wrote:

Not sure about the 98 carb, but this is what I did.

I started with a blown up 2002 and purchased a complete '92 top end. ...more

I don't know who you are.....but you know you're shit on picking the right carb.

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5/23/2015 8:14 PM
Edited Date/Time: 5/23/2015 9:02 PM

Thanks for the information. I made a typo as well, it's an 2003 (not 2002 like I said in the post. I thought it was an 02 model for ages til I checked the VIN when I bought some parts). But I don't think it matters much as far as sizing.

Well I have a spare '98 cylinder so I might just wait til the '03 engine is about to blow and then rebuild it. I'm guessing I'll need pistons and rings to suit that cylinder too.

And that carb is an awesome deal from JD Jetting. I think the jetting kit alone is near on $80. I've read the '07 air boot is also a good mod. My budget is roughly 2k, so this should all fall under.

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5/23/2015 8:18 PM

The 98 cylinder will not work on the 03.

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5/23/2015 8:39 PM

i wouldnt waste the time/effort with the older motor

theyre both slow

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5/23/2015 8:45 PM

CrGuy2T wrote:

The 98 cylinder will not work on the 03.

Correct but i think he mentioned swapping the 98 engine for the 03

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5/23/2015 9:04 PM

CrGuy2T wrote:

The 98 cylinder will not work on the 03.

Any reason why? I'm guessing the powervalve linkage?

If it's just a matter of sizing for the engine swap I might make up some sleeves or whatever for the engine bolts then (I have to do a similar thing for my NSR250 MC21/28 project).

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5/23/2015 9:20 PM

03 the cases were changed. The 98 motor complete will work but you will need to open the motor mounts up bottom and front. The swing arm pivot is the same.

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5/23/2015 9:26 PM

CrGuy2T wrote:

03 the cases were changed. The 98 motor complete will work but you will need to open the motor mounts up bottom and front. The ...more

Interesting. Well thank you for the information. I'll wring the 03 engine out and then look at my options. Worst comes to worse I'll re-purpose the '98 engine for a go kart once I part out the '98 model. I might try the Air Striker carb too.

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5/24/2015 4:14 AM

CrGuy2T wrote:

03 the cases were changed. The 98 motor complete will work but you will need to open the motor mounts up bottom and front. The ...more

KICKERMAN360 wrote:

Interesting. Well thank you for the information. I'll wring the 03 engine out and then look at my options. Worst comes to ...more

Now knowing it's an 03:

Get an 05-07 air boot, the airstriker carb, and Vforce 3/rad valve. That'll wake her up

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Washed up moto and enduro weekend warrior.

5/24/2015 4:56 AM

the 98 engine with a 95 cylinder, piston and matched head and power valve will be one of the best engines you can get fot your 2003 cr 125. i used to have a 99 cr 125 that ran really well with those mods. aldo you can try the stock keihin that comes on your 98 engine instead of buying an air striker. it will run better than the mikuni.

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5/24/2015 7:56 AM

95 cylinders are hard to find (or at least they were for awhile). This was the popular setup for awhile for fmf in '99 and '00.

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6/15/2017 12:48 PM

CrGuy2T wrote:

The motor bolt holes are a tad bit smaller that the the 02. You will need to ream them out. The cylinder swap is fairly easy ...more

I hate to re-open an old thread, but you guys seem like the go-to for cr125 interchange. I have a 1997 that either had the crank seal fall out or a hole in the cases. Pressure checked it and air blew out the oil fill as fast as I could put it in. All the cases for 92-02 have different PN's, but the rumor is all these years are interchangeable. Can anyone confirm what year [if any] cases are compatible with 1997?

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6/15/2017 1:20 PM

Will the 98 engine fit the 97 steel frame? Have a friend wanting to swap in a built 98 Mugen kitted engine into a 97 roller.

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6/15/2017 2:12 PM

newmann wrote:

Will the 98 engine fit the 97 steel frame? Have a friend wanting to swap in a built 98 Mugen kitted engine into a 97 roller.

Yes. All motor mounts in same place up until 2006. Mounting bolts changed size when going to aluminum I believe but not exactly sure what year.

TB901, Cases from 92-97 should be same. Not 100% sure after that I know my '02 bottom end case had a few different things than my 95 era ones do but haven't tried to see if they matched. Anything up to '02 should work if you buy both bottom center cases though...........

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6/15/2017 7:21 PM
Edited Date/Time: 6/15/2017 7:30 PM

Thanks tracktor. Good news, I don't need cases, bad news, the rt side crank seal literally fell out (I half joked about this in my previous post). I have no history on this 20 yo bike. But have rebuilt/raced stuff much older and have never seen this before. Anyone have experience with a similar problem? I fear the next seal might do the same. Any advice/thoughts for installing the new seal would be appreciated.

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