Help with 02 cr125

Dirt Pusher
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Dirt Pusher
Edited Date/Time 9/3/2017 8:44am
I've had my cr125 for a few years now and it was definitely lacking power. The person who I bought it from didn't know how many hours were on the top end but said i should probably rebuild it. So I finally decided to do it and so I replaced the piston, ring, gaskets and the bearing and put it all back together. I then did two heat cycles at idol and then rode it easy for ten minutes. Figured that was solid to let everything seat and break in so I took it out again and got in the throttle and it's still just not all there. I decided to do a compression test and it was only 100psi. Do you think my cylinder needs redone?
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Frodad78
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Frodad78 9/1/2017 10:14am
9/1/2017 10:14am
odds are the powervalve linkage isn't hooked up right. Everyone that buys one of these (including myself) usually has to go in and fix it. Google it, its pretty simple but if its not right it will be a dog. Pull the side cover off the PV on the exhaust side of the head and snap a picture, easy to recognize.
Tracktor
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Tracktor 9/1/2017 10:19am
9/1/2017 10:19am
Hard to say without measurements? Did you put the correctly sized piston in it (A/B/C,etc)? How did cylinder coating look?
What does "not all there mean"? Top/bottom/won't rev out/bogs?
Best break in is one warm up to make sure everything is in correctly and then run it medium hard for a moto. Better ring seal. Heat cycles are for sleeved cylinders.

There is no way to diagnose over the web. These CR125's needed a few things to wake them up obviously mtor needs to be running correctly first-

05+ airboot
38mm Keihin Airstryker carb
5mm exhaust spacer helps a bit to regain low end from bigger carb
03 KX125 pipe modded to fit
If you want more power find an older HPP cylinder

If that is truly your compression you have an issue but every guage reads differently. I had one that always read low no matter what...........


YamahaJT1
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YamahaJT1 9/1/2017 10:41am
9/1/2017 10:41am
Tracktor wrote:
Hard to say without measurements? Did you put the correctly sized piston in it (A/B/C,etc)? How did cylinder coating look? What does "not all there mean"...
Hard to say without measurements? Did you put the correctly sized piston in it (A/B/C,etc)? How did cylinder coating look?
What does "not all there mean"? Top/bottom/won't rev out/bogs?
Best break in is one warm up to make sure everything is in correctly and then run it medium hard for a moto. Better ring seal. Heat cycles are for sleeved cylinders.

There is no way to diagnose over the web. These CR125's needed a few things to wake them up obviously mtor needs to be running correctly first-

05+ airboot
38mm Keihin Airstryker carb
5mm exhaust spacer helps a bit to regain low end from bigger carb
03 KX125 pipe modded to fit
If you want more power find an older HPP cylinder

If that is truly your compression you have an issue but every guage reads differently. I had one that always read low no matter what...........


Heat cycles are not merely for sleeved cylinders...Wow. It all depends upon the work that was done. Best advice is that he seek a competent mechanic if he lacks the wherewithal to do the work himself.
Dirt Pusher
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Dirt Pusher 9/1/2017 10:46am
9/1/2017 10:46am
Tracktor wrote:
Hard to say without measurements? Did you put the correctly sized piston in it (A/B/C,etc)? How did cylinder coating look? What does "not all there mean"...
Hard to say without measurements? Did you put the correctly sized piston in it (A/B/C,etc)? How did cylinder coating look?
What does "not all there mean"? Top/bottom/won't rev out/bogs?
Best break in is one warm up to make sure everything is in correctly and then run it medium hard for a moto. Better ring seal. Heat cycles are for sleeved cylinders.

There is no way to diagnose over the web. These CR125's needed a few things to wake them up obviously mtor needs to be running correctly first-

05+ airboot
38mm Keihin Airstryker carb
5mm exhaust spacer helps a bit to regain low end from bigger carb
03 KX125 pipe modded to fit
If you want more power find an older HPP cylinder

If that is truly your compression you have an issue but every guage reads differently. I had one that always read low no matter what...........


That's exactly how I broke it in. I know it's stock bore so yes I put the right size piston In it and it's pretty much stock except for pro circuit expansion pipe, silencer and a boysen reed valve. I just took it out and actually ran it hard and it definitely runs better than before but It has no low end and the high end seems ok but I just don't feel like it is 100%. Maybe I'm just used to a 450. Should a 125 pull up the front wheel pretty hard in 2nd?

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Dirt Pusher
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Dirt Pusher 9/1/2017 10:51am
9/1/2017 10:51am
Tracktor wrote:
Hard to say without measurements? Did you put the correctly sized piston in it (A/B/C,etc)? How did cylinder coating look? What does "not all there mean"...
Hard to say without measurements? Did you put the correctly sized piston in it (A/B/C,etc)? How did cylinder coating look?
What does "not all there mean"? Top/bottom/won't rev out/bogs?
Best break in is one warm up to make sure everything is in correctly and then run it medium hard for a moto. Better ring seal. Heat cycles are for sleeved cylinders.

There is no way to diagnose over the web. These CR125's needed a few things to wake them up obviously mtor needs to be running correctly first-

05+ airboot
38mm Keihin Airstryker carb
5mm exhaust spacer helps a bit to regain low end from bigger carb
03 KX125 pipe modded to fit
If you want more power find an older HPP cylinder

If that is truly your compression you have an issue but every guage reads differently. I had one that always read low no matter what...........


YamahaJT1 wrote:
Heat cycles are not merely for sleeved cylinders...Wow. It all depends upon the work that was done. Best advice is that he seek a competent mechanic...
Heat cycles are not merely for sleeved cylinders...Wow. It all depends upon the work that was done. Best advice is that he seek a competent mechanic if he lacks the wherewithal to do the work himself.
Why would I do that? Some people enjoy learning and working on there own stuff. Asking for pointers does not mean I'm incapable.
SKIDLID
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SKIDLID 9/1/2017 10:53am
9/1/2017 10:53am
Sounds like a powervalve not hooked up right. Is the airbox full of fuel? If so the reed vavle is not shutting. Could be a chipped, warped or bad reed.
Dirt Pusher
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Dirt Pusher 9/1/2017 11:01am
9/1/2017 11:01am
SKIDLID wrote:
Sounds like a powervalve not hooked up right. Is the airbox full of fuel? If so the reed vavle is not shutting. Could be a chipped...
Sounds like a powervalve not hooked up right. Is the airbox full of fuel? If so the reed vavle is not shutting. Could be a chipped, warped or bad reed.
No but I my carb constantly leaks fuel from the over flow. My floats are working perfectly fine and I've heard people say that is from a missing O ring on the main jet. Would that cause any power loss?
Dirt Pusher
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Dirt Pusher 9/1/2017 11:05am
9/1/2017 11:05am
Frodad78 wrote:
odds are the powervalve linkage isn't hooked up right. Everyone that buys one of these (including myself) usually has to go in and fix it. Google...
odds are the powervalve linkage isn't hooked up right. Everyone that buys one of these (including myself) usually has to go in and fix it. Google it, its pretty simple but if its not right it will be a dog. Pull the side cover off the PV on the exhaust side of the head and snap a picture, easy to recognize.

Do I have to pull the the side of my case to adjust it?


YamahaJT1
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YamahaJT1 9/1/2017 11:10am
9/1/2017 11:10am Edited Date/Time 9/1/2017 11:12am
Dirt Pusher wrote:
Why would I do that? Some people enjoy learning and working on there own stuff. Asking for pointers does not mean I'm incapable.
Head on over to the "Tech Help/Race Shop" forum...

Awesome for you to give it a go!
YamahaJT1
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YamahaJT1 9/1/2017 11:16am
9/1/2017 11:16am Edited Date/Time 9/1/2017 11:37am
Frodad78 wrote:
odds are the powervalve linkage isn't hooked up right. Everyone that buys one of these (including myself) usually has to go in and fix it. Google...
odds are the powervalve linkage isn't hooked up right. Everyone that buys one of these (including myself) usually has to go in and fix it. Google it, its pretty simple but if its not right it will be a dog. Pull the side cover off the PV on the exhaust side of the head and snap a picture, easy to recognize.
Dirt Pusher wrote:
Do I have to pull the the side of my case to adjust it? [img]https://p.vitalmx.com/photos/forums/2017/09/01/212459/s1200_1504289112770121930267.jpg[/img]

Do I have to pull the the side of my case to adjust it?


Man that is wet... Seals are shot. Monkey on the head nut as well.

Go to Race Tech Help/Race Shop forum

EDIT: Oh yeah, nice retainer "clip". Replace immediately... Tranny/drive at peril. Do not let that little "clip" fall into the opening below it! Get a rag and cover the opening below it! NOW! You can do this!
Tracktor
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Tracktor 9/1/2017 11:21am
9/1/2017 11:21am
YamahaJT1 wrote:
Heat cycles are not merely for sleeved cylinders...Wow. It all depends upon the work that was done. Best advice is that he seek a competent mechanic...
Heat cycles are not merely for sleeved cylinders...Wow. It all depends upon the work that was done. Best advice is that he seek a competent mechanic if he lacks the wherewithal to do the work himself.
As a general rule yes they are due to aluminum & steel expanding at different rates. There is no benefit to breaking in an MX bike through multiple heat cycles. It's detrimental to ring seal as the more ring pressure the better they seat & you only have a short window to do that.. I have been doing it this way for many years on more motors than I can count and find little blowby when rebuilding and not one failure, period. Feel free to do whatever you think is best, however..............
YamahaJT1
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YamahaJT1 9/1/2017 11:52am
9/1/2017 11:52am Edited Date/Time 9/1/2017 11:57am
Tracktor wrote:
As a general rule yes they are due to aluminum & steel expanding at different rates. There is no benefit to breaking in an MX bike...
As a general rule yes they are due to aluminum & steel expanding at different rates. There is no benefit to breaking in an MX bike through multiple heat cycles. It's detrimental to ring seal as the more ring pressure the better they seat & you only have a short window to do that.. I have been doing it this way for many years on more motors than I can count and find little blowby when rebuilding and not one failure, period. Feel free to do whatever you think is best, however..............
Yeah, for "Top end" replacement only I agree... Anything that requires a case split, heat cycles are beneficial IMHO to let everything settle in for a few expansion/contraction cycles before RIPPIN' on it. Dissimilar metals, Young's Modulus, and all...

"Tongue in Cheek"... Please take no real offense! LOL! Just a "selfie" during a recent rebuild.



Let us head over to the other forum and help the OP...

YamahaJT1
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YamahaJT1 9/1/2017 12:47pm
9/1/2017 12:47pm Edited Date/Time 9/1/2017 12:48pm
No replies. over and OUT. Good Luck.
Frodad78
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Frodad78 9/1/2017 1:06pm
9/1/2017 1:06pm
Dirt Pusher wrote:
Why would I do that? Some people enjoy learning and working on there own stuff. Asking for pointers does not mean I'm incapable.
YamahaJT1 wrote:
Head on over to the "Tech Help/Race Shop" forum...

Awesome for you to give it a go!
Well it appears to be loaded correctly, if it wasn't it wouldn't be resting on that pin to the left.

I had an 01 and it took quite a bit of work to wake it up. I have a 36mm PWK that I had on mine, been trying to sell it to a CR owner for a while now haha.
cmotodad
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cmotodad 9/1/2017 9:07pm
9/1/2017 9:07pm
What are you wanting for the airstriker?
burn1986
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burn1986 9/1/2017 9:26pm
9/1/2017 9:26pm
Those bikes need way more air too. Someone mentioned 05+ airbox, plus I would even think about some extra air holes in the side plates as well.
ClassCClairVoyant 9/3/2017 6:49am
9/3/2017 6:49am
I owned the '00 thru '03 CR125's and if I remember right, in '02 Honda went with the larger carb (38mm?) and weird intake manifold to get competitive hp. The weird intake being a manifold and stuffer with very small passages. It worked except the bikes had zero low end making them hard to ride for your average rider. To bring back some low end you can use a Tassinari reed block and flow the manifold to match. But, just as big a problem with those bikes in my opinion is the cylinder being out of round. You don't need micrometers to tell that the piston is excessively loose around the exhaust port. If you are on a budget and can't afford to get your cylinder replated try a ProX incremental oversize piston (as mentioned above). I always used a 'C' size. That will tighten up the clearances enough to bring back some punch. I've tried all the other suggestions above and they work great just remember you may have to jet the bike to reap the benefits.

On a side note... a one inch lowering link on the back and raising the forks 3/4 inch in the clamps with dramatically improve the handling of that bike.
YamahaJT1
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YamahaJT1 9/3/2017 7:33am
9/3/2017 7:33am Edited Date/Time 9/3/2017 7:45am
The OP never replied in the Tech Help/Race Shop.

When the mechanical RC/Power Valve weeps spooge like that into the cover area, it is 99% because carbon buildup has forced its way outward and abrasively eroded the seals and robs performance. Look and the retainer clip and head nut... Not the work of anyone competent.

Piston sizing? Squish? Ring gap? We all have our own "special" methods. I prefer actual measurements... Not being an asshole here. Makers provide specifications for a reason.

Every top end replacement should include RC/Power Valve cleaning at minimum to ensure top performance. YMMV.







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YamahaJT1
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YamahaJT1 9/3/2017 8:15am
9/3/2017 8:15am Edited Date/Time 9/3/2017 8:44am
Guess I should have posted "Eli" or "Herlings" in the reply. Wink

Moderately surprised that "Loots" or "Yep" hasn't kicked me in the teeth in this thread...

Tracktor
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Tracktor 9/4/2017 7:49am
9/4/2017 7:49am
Tracktor wrote:
As a general rule yes they are due to aluminum & steel expanding at different rates. There is no benefit to breaking in an MX bike...
As a general rule yes they are due to aluminum & steel expanding at different rates. There is no benefit to breaking in an MX bike through multiple heat cycles. It's detrimental to ring seal as the more ring pressure the better they seat & you only have a short window to do that.. I have been doing it this way for many years on more motors than I can count and find little blowby when rebuilding and not one failure, period. Feel free to do whatever you think is best, however..............
YamahaJT1 wrote:
Yeah, for "Top end" replacement only I agree... Anything that requires a case split, heat cycles are beneficial IMHO to let everything settle in for a...
Yeah, for "Top end" replacement only I agree... Anything that requires a case split, heat cycles are beneficial IMHO to let everything settle in for a few expansion/contraction cycles before RIPPIN' on it. Dissimilar metals, Young's Modulus, and all...

"Tongue in Cheek"... Please take no real offense! LOL! Just a "selfie" during a recent rebuild.



Let us head over to the other forum and help the OP...

Seriously? The original post was about a top end rebuild not a full engine rebuild. Basically you argued with me then back peddle to agree with me? Gotta love Vital.............

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