Just bought a cr125 2003......please give me your .02!!!

Just picked up this 2003 CR125 a few days ago. The bike seems to be in pretty good shape, I am going to give a pretty thorough look over and cleaning before riding season starts, just looking for some feedback.

So far I am planing on the following:

-air filter/oil change/spark plug

-boyseen rad valve

-Carb cleaning

-07 air intake tract

-Open up air box using uni 1" vents

-Check compression

-flush brake and coolant fluids

-new grips, tighten chain and clean

-check bearing and all suspension joints

I also ordered a new rear rotor, the factory one is slightly bent. I have only ridden the bike for like 3 minutes, but it seems to run well. Idles perfect and starts 1st kick every time even ice cold. I also noticed that the rear wheel has a very slight bend/bulge on one side of the rims sidewall. Ill post a picture of that tomorrow.

Let me know what you think and also let me know what else to check for....thanks guys!




No one has any opinions or advice....?

Pull off the pipe and have a look into the cylinder to see what the piston and cylinder look like before you invest any further money into it. I made the mistake of not looking into mine when I bought it and now I need to replace/replate the cylinder, new head, piston etc.

clean it up real nice, change all fluids, check brakes, spokes, and like northwoods said check the cylinder, piston and rings to see if those are in good condition. i just bought a 02 cr 125 like 3 months ago and changed all my fluids and cleaned the carb and everything.

I just pulled the exhaust off and the piston shows some wear for sure, ill post some pictures up in a minute. I also checked the compression when the bike was ice cold and got 120psi and then again with a squirt of oil in the spark plug hole and I got 130psi.

Assuming the piston and cylinder are in ok shape do you think its good to run, or is it about time for a top end? I looked through the service manual and could not find the OEM compression spec. does anyone know it?

Looks like the rad is tweated in the first picture? or is that my four eyes screwing up again

yeah your right the left side radiator is pushed in a little. It doesn't leak, but it is dented.

here are some pictures of the piston top and bottom and the cylinder wall through the exhaust port. let me know what you think!

just to reiterate compression is 120psi cold and 130psi cold with a squirt of motor oil in the spark plug hole.

This is the exhaust side picture of the piston and ring:


Picture of the skirt of the piston, closest to the top of the stroke as possible:


Last one of the intake side cylinder wall:


From what I am reading here, it sounds like 120-130psi is kinda low correct? Is stock supposed to be 160-180 like I have read?

Thats low...pull the cylinder....check for scars in the nikasil plating. The piston does not look so good. I wouldn't run it any until the cylinder is checked out. You may get lucky and just be able to replace the piston.

Leave it alone and run the crap out of it till it blows haha, soon as you fire up a fresh top end it'll have light scoring in it all over again.

Ok I just pulled the head off the top of the cylinder and I have bad news and good news!

bad news: the head has all sorts of pitting and damage from some PREVIOUS top end failure.

good news: the cylinder looks good, no scaring, scratches or pitting!!!

Looks like I am going to have to do piston and rings and replace the head. But the cylinder looks good to go and I measured it with my calipers and its within specs according to my honda service manual.

Check out the pictures and tell me what you think!






Do you think I need to replace that head? I am thinking yes, but not sure if those mark and indentations are bad for proper combustion. Also, I am looking around at top end kits, and the Weisco seems to have 2 different pistons for the 03 cr125r. Do you guys have any recommendation on what piston and ring kit to use?

Thanks for all the help and comments so far! This forum seems to be a great spot to learn!

before getting a new head, check the squish clearance. You may be able to machine that out reshaping the dome

before getting a new head, check the squish clearance. You may be able to machine that out reshaping the dome

Is it really worth trying to have it fixed when I can buy a brand new one for $70 and it will definitely work well?

You can get used heads on ebay for $35....Or have yours decked and reshaped for about $40.

Did you pull the ring from the piston and check the ring end gap?

correct squish is worth it's weight in gold when it comes down to jetting and engine performance...

A new head wont give you that. If you where to machine a head why not machine your old one then your already $70 bucks in front?

If your not worried about squish clearance then just get the new head. Basically i was just giving you an option.

Well I have really not learned much about squish, if its worth while to get the head cut and to get the squish where it needs to be then I am all about it.

I remember a while back when building my banshee, I read about how to measure it. Is there a link anyone has to a thread that explains this?

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