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slow_poke 04-23-2014 06:03 PM

'02 CR125 Rebuild
After years of not riding but wanting to and my oldest now able to get along on his crf50 by himself, I finally pulled the trigger on a '02 CR125 that has clearly seen better days so that I can rebuild/restore when I have free time between work/kids/grad school. I bought the bike for more than I should have now that I pulled it apart and seen what all I need to replace/fix. I picked it up and brought it how and immediately started tearing it down with the intention of having it back up and running before May, well thats now out of the question and I figure I will take my time and make this a bike that I have always wanted.

Tonight I pulled the head and cylinder off to take a look and see what I need to replace in the motor. I found that the head looks to be destroyed from something hard getting bounced around. I am just going to assume that it was a spark plug piece due to the bike having a brand new plug installed when I brought it home.

The flaps look to have never been cleaned in the 12 years since they were installed from the factory but should clean up nicely. I wil have to replace the flap shaft bearing in the cylinder though. It is completely shot.

The crank has been replaced at some point with a Wiseco replacement. It seems to be in good shape with no up and down play and only minimal side to side movement, which from my understanding is ok. It does have a small mark on the rod but I am not sure what it could have been from. Once I can post photos, I will.

Lastly, the cylinder seems to be in good shape with good crosshatching still visible. I will need to mic it to make sure it is still usable but it should clean up nicely if the size is in spec.

Overall I expected much worse before cracking the top end open. The outside of the bike was severly lacking on maintence. Once I can post photos I will do so of my findings and get the expert(you guys) opinions on my findings.

slow_poke 04-23-2014 08:16 PM

Just finishing up bagging and tagging parts for the night and I decided to throw the ring down into the cylinder and measure the gap and I found that it was at .028. What are some of the issues with ring gap set to large? Loss of compression?

---------- Post added at 07:16 PM ---------- Previous post was at 07:14 PM ----------

Randog Leader 04-25-2014 09:32 AM

Yes, cylinder does look good from the pics that you posted. Question is: What size is the bore? I would get a mic and a dial bore gauge and see what you have. It may be beneficial to get an oversized piston and new ring. Pro-x goes all the way up to a size "D", which can get you the proper piston to cylinder clearance if it is close to stock but a bit over.

And yes, I would have the head turned to get rid of that crap. If it can't be turned, I would get another one off of Flea-Bay.

Good luck!

slow_poke 04-28-2014 10:42 AM

Thanks for the tip on Pro-X. I had not looked at their products, I was simply going to size up a A or B OEM and see which one worked better.

I got a chance to snap some photos of the piston top and bottom. COrrect me if I am wrong but it seems to have been run a bit rich right? This being the first 2 stroke I have owned.

JMV 04-28-2014 11:14 AM

That brown residue on the bottom of the piston is an indication of a lean condition. The piston gets hot, and the fresh charge in the crankcase gets hot on the bottom of the piston and leaves that mark there.

stevo450 04-28-2014 12:31 PM

This should point you in the right direction........

bbrmotosports 04-29-2014 05:34 AM

That head is savable. You can either get it shaved and rechambered. Or you can simply just knock down the high spots with emery cloth and run it. The high spots are what causes hot spots on the piston.

slow_poke 04-29-2014 06:25 AM

I looked at a few companies online and I am looking at 55-70 to get the head turned. I could just a easy get a oem head for 59 from partzilla.

I didnt think that you could sand down a head by hand, it would alter it too much?

Randog Leader 04-29-2014 08:08 AM

Is it really that cheap? Get a new one, then.

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