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CR125: six speed tranny swap

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For those of you that don't like your five speed transmission in your 1998 to 2007 CR125, but otherwise love your CR, there is hope.  I am posting this to share what I have successfully done to my 2005 CR124/144.

 

I stumbled on to this while googling.  

 

http://metal-matrix.com/stockmoto/index4.html

 

So I found a 1997 CR125 six speed transmission on ebay and bought it.  First thing I noticed was that the countershaft sprocket from my 05 didn't fit… problem!  As it turns out, I was having EG do my top end conversion to 144 at this time, so I called Eric and asked him about the six speed tranny swap.  He told me that the countershaft problem was not a big deal as long as the outer diameter of the counter shaft bearing was the same.  And luckily it is.

 

Short story is:  you can take any 1998 to 2007 CR125, and do this conversion.  For 2004 to 2007, this requires changing countershaft bearings and seal to 2003 or earlier parts.  The swap is a simple remove and replace the complete set of transmission parts.  (shaft, countershaft, shift forks, and drum)

 

The shifter kart industry also uses the CR125 motor and in fact you can purchase new a 1999 CR125 motor set up for kart with a 1997 six speed.   Means the kick-starter is missing.  See also:

 

http://www.fastech-racing.com/honda-cr125-engines/

http://www.swedetechracing.com/moto_honda_125cc_engine.html

 

And yes, Service Honda's CR125AF comes with a 1999 engine, and 1997 six speed transmission.  Why service honda chose the 99 engine vs the 05 to 07 engine, I have no idea.  But they did choose the six speed!  Why?  Perhaps some of you motor experts can comment.

 

http://www.dirtrider.com/features/service-honda-cr125af/

 

I've seen this topic come up here and there, but thought it deserved it's own string in the Honda Two Stroke section.  I really really like my six speed CR144.  Have had no transmission issues.  

 

BTW:  here are the comparative 6 vs 5 ratios.

 

1.  2.357  vs  2.308

2.  1.867  vs  1.867  same

3.  1.526  vs  1.529  I think the latter might be misprint, and is actually 1.526 as well

4.  1.286  vs  1.294

5.  1.130  vs  1.130  same

6.  1.000       

 

http://world.honda.com/news/2004/2041122.html

http://srsengines.com/technical-library/shifter-kart-engines/best-stock-honda-cr125-shift-points

 

Like if you appreciate this info.  If you have done, or plan to do a six speed conversion, please post.

 

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Great info magpie5. I plan on doing this in the future but I have an 04 cr125, I don't know if you know much about the 04's but they were bastard single year engine with electronic power valves that have the lowest HP out of all the years. So I plan on getting rid of my 04 completely and building a complete 90-97 engine from the ground up. And I've heard that the pv's out of the 98's were best also. So I'm gonna give that a shot too. Anyways thanks for the great info an links! Makes things a little easier!

*2smokin*

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Great info magpie5. I plan on doing this in the future but I have an 04 cr125, I don't know if you know much about the 04's but they were bastard single year engine with electronic power valves that have the lowest HP out of all the years. So I plan on getting rid of my 04 completely and building a complete 90-97 engine from the ground up. And I've heard that the pv's out of the 98's were best also. So I'm gonna give that a shot too. Anyways thanks for the great info an links! Makes things a little easier!

*2smokin*

Thanks Smokin!  Yeah I knew that the 04's were bastards.  But you have a good gen3 aluminum frame to build off of.    I'd perhaps go with a 99 engine/97 six speed combo.  I'm sure Service Honda could sell you one for an arm and a leg.  I know the 05-07 engines are pretty darn good once you get rid of the stock mikuni carb.  Good luck with the build.

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Haha! I wish I had deep enough pockets for a service honda engine! Fortunately I like building things myself. 97/99 is definitely the route I'm gonna go. I don't know if you've seen this post or not,

http://www.thumpertalk.com/topic/1029232-ultimate-cr125-motor/

This guy niño really knows his stuff! I'm basically gonna use thi post as a parts list. And I don't k ow if you know much about mugen cylinders, but after some research I'll proly spend the rest o my days looking for one of these things!!! I won't consider my bike complete until it has one. Lol

*2smokin*

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I'm not sure on the details of why they stopped making them, but from what I've gathered, their not on just any bikes, you have to find a bike that was once ridden by a pro or was owned by a mugen parts distributor. I'd sure like to find somebody that knows these details to school us on these rare cylinders.

*2smokin*

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Mugen used to offer the parts for sale as a kit you could of bought think it was like a grand back in 1991 dollars that was a lot  and to be honest it wasn't that much better then a well setup stocker but it looked trick with the cooling fins on the cylinder on the line racing used to sale the kit state side back then. Mugen stopped making them then because they got into modding honda cars instead and thier kits never really sold that well anyways.

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That being said, if this is to be believed, Honda literally added a sixth gear on top of 5th if we compare the 90' tranny vs the late one.

 

http://www.thumpertalk.com/topic/1086470-cr125-six-speed-tranny-swap/

 

I'd be curious to compare these ratios with the yz transmission.

 

EDIT: Here it is. Seems like the yz has smaller gears across the range.

  • 2.385 vs 2.357 (0.028)
  • 1.933 vs 1.867 (0.066)
  • 1.588 vs 1.526 (0.062)
  • 1.353 vs 1.286 (0.067)
  • 1.200 vs 1.130 (0.07)
  • 1.095 vs 1.000 (0.095)   

 

Honda didn't add a gear, they subtracted it.  Thanks for the yz comparison!

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Honda didn't add a gear, they subtracted it.  Thanks for the yz comparison!

Yeah, wrong choice of words here but it made more sense in the context of the other thread. ;)

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Does anyone know the difference between the hpp clutch baskets and clutches compared to the newer ones? I think it changed in 95 or 96?

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Mugen used to offer the parts for sale as a kit you could of bought think it was like a grand back in 1991 dollars that was a lot  and to be honest it wasn't that much better then a well setup stocker but it looked trick with the cooling fins on the cylinder on the line racing used to sale the kit state side back then. Mugen stopped making them then because they got into modding honda cars instead and thier kits never really sold that well anyways.

Your info is almost correct BUT the Mugen kit offered a huge improvement over stock. That said i still race my 1990 Mugen kitted engine against todays machinery and i don't have a real disadvantage when i'm racing against a '14 KTM...

That's with a 24 year old engine !! Just imagine what your were looking at at the time...rest assured such a engine was leaps faster than all the rest.

 

Back on topic:

why anybody would need a 6th gear is a mystery to me. If you are a woods racer or using your bike for enduro riding with much higher speeds ok, but on a MX track you definitely don't need a 6th gear. BUT i know a lot of guys put like 53t rear chainrings on their bikes which makes them really short...you loose 1st gear and might need one more on top. Bad idea! It might feel faster if you have an engine that runs through its gears faster but in reality you are standing still. I on the other hand used to run even smaller chainring (49t instead of the stock 51) to get higher gearing and therefore you can actually use the engines power and have to shift way less. At least with a powerful engine this is the way to go. It lets you go through corners without having to shift midway through. I can do 1st gear starts and beat most to the 1st corner as my rear doesn't spin like crazy when i let the clutch out and i have to shift at least one gear less...the moment i went to a higher gearing i was getting the starts. Today, at age 46 and 16 years off of racing championships, i went back to a slightly lower 50t though. It is still 1 teeth smaller than the stock 51t chainring but i'm not able to keep the speed and revs up in corners as i used to do back in the day. But trying out 51t or 52t i feel my engine is sceaming loud underneath but i'm really standing still.

 

I actually have 3 different 125s and each of them has it's Mugen kit:

 

From left to right:

1990/91 VRP Mugen CR 125 with '90 Mugen (with custom aluminium frame!)

1998 CR 125 with '91 Mugen

2012 CR 125 AF with '90 Mugen

 

13483689804_a4f6603be7_c.jpg

 

13483440613_78db111469_c.jpg

 

Edited by nino
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Maybe I am wrong in this assumption but I had thought that the 5 speed made 1st gear taller, kind of like combining 1st and 2nd gear so the top speed of the 5 and 6 were comparable.  If this was the case, the 6 speed would be a better "play" bike since using 1st on trails would be easier than a taller 1st from a 5 speed.  My 94 125 works pretty well in all types of riding because 1st is not nearly as tall as 1st was on either my 450 or my 250.  I've never ridden any of the 5 speed 125's so I can't compare them personally.  Maybe someone here who has both or ridden both can answer this question.

Edited by frdbtr

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Your info is almost correct BUT the Mugen kit offered a huge improvement over stock. That said i still race my 1990 Mugen kitted engine against todays machinery and i don't have a real disadvantage when i'm racing against a '14 KTM...

That's with a 24 year old engine !! Just imagine what your were looking at at the time...rest assured such a engine was leaps faster than all the rest.

 

Back on topic:

why anybody would need a 6th gear is a mystery to me. If you are a woods racer or using your bike for enduro riding with much higher speeds ok, but on a MX track you definitely don't need a 6th gear. BUT i know a lot of guys put like 53t rear chainrings on their bikes which makes them really short...you loose 1st gear and might need one more on top. Bad idea! It might feel faster if you have an engine that runs through its gears faster but in reality you are standing still. I on the other hand used to run even smaller chainring (49t instead of the stock 51) to get higher gearing and therefore you can actually use the engines power and have to shift way less. At least with a powerful engine this is the way to go. It lets you go through corners without having to shift midway through. I can do 1st gear starts and beat most to the 1st corner as my rear doesn't spin like crazy when i let the clutch out and i have to shift at least one gear less...the moment i went to a higher gearing i was getting the starts. Today, at age 46 and 16 years off of racing championships, i went back to a slightly lower 50t though. It is still 1 teeth smaller than the stock 51t chainring but i'm not able to keep the speed and revs up in corners as i used to do back in the day. But trying out 51t or 52t i feel my engine is sceaming loud underneath but i'm really standing still.

 

I actually have 3 different 125s and each of them has it's Mugen kit:

 

From left to right:

1990/91 VRP Mugen CR 125 with '90 Mugen (with custom aluminium frame!)

1998 CR 125 with '91 Mugen

2012 CR 125 AF with '90 Mugen

 

 

Nino, you really have a nice collection.  Very enviable!  And your answer is perfect.  Really there is no need for sixth gear on a track.  That must have been Honda's mindset when they changed to a five.  But just like you said, for enduro, desert, etc, 6th gear is really nice to have.  So Honda took no consideration for the rest of the market.  BTW:  I was wondering if a Mugen kit would fit on a 2005 - 2007 CR.  I'd love to get one.

Edited by magpie5
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Now here's the long story:  

 

My first CR125 was a 1982 model back in the day I was 15 years old.  Great bike for the time and I really had a lot of fun.  I never made a conscious choice leave the sport, but eventually stopped riding because as a kid I couldn't afford to maintain my bike, and life went on.  

 

Roughly 30 years later I bought my second CR125, 2010 model.  I fell in love with the bike the moment I test rode it, but didn't realize it was only a 5 speed at the time.  Then gradually I began to be dissatisfied with the bike only because I found myself too often trying to shift to sixth gear that wasn't there.  

 

I like to do all types of riding and only spend a fraction of my time on a track.  My favorite is alpine jeep trails in the woods with hill climbs.  Don't need sixth gear for that either.  I would have sold this bike if I hadn't discovered the possibility of the six speed tranny swap from the shifter kart folks.  With the PWK, the 144 big bore, and the six speed, this bike is a keeper.

Edited by magpie5

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Maybe I am wrong in this assumption but I had thought that the 5 speed made 1st gear taller, kind of like combining 1st and 2nd gear so the top speed of the 5 and 6 were comparable.  If this was the case, the 6 speed would be a better "play" bike since using 1st on trails would be easier than a taller 1st from a 5 speed.  My 94 125 works pretty well in all types of riding because 1st is not nearly as tall as 1st was on either my 450 or my 250.  I've never ridden any of the 5 speed 125's so I can't compare them personally.  Maybe someone here who has both or ridden both can answer this question.

 

To answer your question, I have ridden both 5 and 6 speed on the same bike!  Hello!  

 

Notice from the six vs five comparison:

 

           Six vs Five

 

1.  2.357  vs  2.308

2.  1.867  vs  1.867  same

3.  1.526  vs  1.529

4.  1.286  vs  1.294

5.  1.130  vs  1.130  same

6.  1.000  vs  deleted/missing/not there anymore

    

Fifth gear is identical for both at 1.130.  First through fourth is nearly identical, first being slightly shorter on the six speed.  So effectively sixth gear was just deleted from the set when Honda went to the five speed.  Try riding your 94 without using 6th gear.  That is what the 5 speed is like.

 

If you check out the specs on this link:

 

http://world.honda.com/news/2004/2041122.html

 

It shows the late model 125 and 250 gearing side by side.  250's fifth is 1.000 equals earlier 125 sixth.  The 250 version of the 125 five speed would be a four speed.  How many 250 riders out there would like to give up fifth gear?  Seriously, how often do you use fifth gear on a track?  I know there is interest out there instead for a six speed 250, or a wide ratio 5 speed.

Edited by magpie5

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I have both - In total i have 4 different HPP engines, 6 speed and 5 speed  (98/99) and i can't tell a difference. 6th is never ever needed anyway and 1st through 5th i can't tell if one is different than the other!

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I don't mx, but with six gears you could gear the the bike down for more low speed grunt and have sixth for more speed. Makes the bike a lot more versitility for offroad or play.

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I'm in.the process to do this swap on my 2006. Time wasted or.... I do woods and I ride a 13/53 ratio at the moment.

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I'm in.the process to do this swap on my 2006. Time wasted or.... I do woods and I ride a 13/53 ratio at the moment.

 

Is this a question?  Not sure I understand what you are asking...

 

Keep us posted on your swap.  

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