Rebuilding the KX125...

[DirtyJoe]

Well, I just picked up this bike and at the time, all it needed was a new ring (piston). Replaced it...

Well, I get about a tanks use out the bike and all of a sudden, the motor slowly (within seconds) dies out.

I take the motor apart, AGAIN, and find the new wiseco piston is all pitted on the top with scorn sides, and the ring is stuck in the piston.

My concluded that a piece of the old ring was still in the crankcase and finally got sucked up into the chamber. But, it does confuse me a bit. there was what looked like brass/copper shavings in the motor. What could this have been?

Now, with my Question....

I noticed the rod moves back and forth on the crank. Is this normal?

Also, I Does anyone have a good detailed picture on the motor/trans. I'm not sure if I put the trans gears in the right order and I would like to see a picture to make sure.


Thanks guys.

 

[dezryder]

Your kidding right? You did major motor and trans work without a manual?

 

[DirtyJoe]

Your kidding right? You did major motor and trans work without a manual?

Yes, I did. Ive been building cars and hotrods for over ten years, ASE Certified (but choose a different line of work)

Motors come very natural to me. But, being the first time with a bike motor (other than Harley) I wanted to make sure I do have everything in order before I try to crank the sucker over.

 

[dezryder]

My questions then...

Well, I just picked up this bike and at the time, all it needed was a new ring (piston). Replaced it...

Well, I get about a tanks use out the bike and all of a sudden, the motor slowly (within seconds) dies out.

I take the motor apart, AGAIN, and find the new wiseco piston is all pitted on the top with scorn sides, and the ring is stuck in the piston.

My concluded that a piece of the old ring was still in the crankcase and finally got sucked up into the chamber. But, it does confuse me a bit. there was what looked like brass/copper shavings in the motor. What could this have been?

Why didn't you flush out the crank case with solvent when it was apart to make sure it was clean?

Now, with my Question....

I noticed the rod moves back and forth on the crank. Is this normal?

A shop manual will give you the proper tolerance's.

Also, I Does anyone have a good detailed picture on the motor/trans. I'm not sure if I put the trans gears in the right order and I would like to see a picture to make sure.

Again, with a shop manual, this would be answered.

Thanks guys.

Just curious, how did you arrive at the torque values on assembly?

I'm not trying to harsh your buzz here, just curious how you got by without a shop manual. And with that said, maybe you wouldn't be asking these questions if you had one for reference.

I'm not ASE certified, but have in my past (many years ago) worked as a mechanic. (auto's) I consider myself a fairly decent M/C mechanic, but would not tackle an engine/trans teardown and rebuild without a shop manual. (by myself)

Also, I have never taken any bike of mine to a shop. I do all my own wrenching, on my kids bikes as well. I have also done service work for a dealer friend on weekends in the past. (Husky's and KTM's)

IMHO, there's no substitute for a good shop manual...period.

Good luck with your bike rebuild.

 

[healeyboy76]

I had the same thing happen to an 85 cr 125 a few years ago. The damage to my engine sounds identical to yours. It turned out that the lower rod bearing was eaten up and thats what caused the damagae. With the rod, a little side to side movement is ok, but its the up and down you want. I did not find out that it was the bearing until i pulled out the crank because where the part of it was missing was on the bottom and i could not see it by turning the crank with the motor together. Good luck

 

[DirtyJoe]

Just curious, how did you arrive at the torque values on assembly?

I'm not trying to harsh your buzz here, just curious how you got by without a shop manual. And with that said, maybe you wouldn't be asking these questions if you had one for reference.

I'm not ASE certified, but have in my past (many years ago) worked as a mechanic. (auto's) I consider myself a fairly decent M/C mechanic, but would not tackle an engine/trans teardown and rebuild without a shop manual. (by myself)

Also, I have never taken any bike of mine to a shop. I do all my own wrenching, on my kids bikes as well. I have also done service work for a dealer friend on weekends in the past. (Husky's and KTM's)

IMHO, there's no substitute for a good shop manual...period.

Good luck with your bike rebuild.

No Offence taken.

About the TQ specs. I didnt take anything apart except the Jug. And Obviously the piston has no bolts or nuts to TQ down. So basicly the 4 Jug bolts is all I removed and re-installed. Ill be honest, I didnt TQ them down to any specs but then again, I didnt see why they needed it either. Or should I say, critical.

About flushing the crank case. I never had it apart. I do now, lol. I dont think it was in there the whole time. I think it blew on me after the rebuild. I noticed there is no way this piece of bearing had enough room to float around the crankcase without jambing the motor up.

 

[kilroy]

Dirty Joe,I just bought my 1997 kx125.It needs the same thing done on the top end.What year is yours?And if it's a 95 or newer,is it just the 4 jug bolts to get it off,as it looks?Hat's off to ya' on getting this far.I see alot of chastizing for you not having a manual,but no answers to your questions...what's up with this site?I have a manual coming in the mail in the next couple days..I'll be keeping an eye on this thread.. :nod:

 

[dezryder]

No Offence taken.

About the TQ specs. I didnt take anything apart except the Jug. And Obviously the piston has no bolts or nuts to TQ down. So basicly the 4 Jug bolts is all I removed and re-installed. Ill be honest, I didnt TQ them down to any specs but then again, I didnt see why they needed it either. Or should I say, critical.

About flushing the crank case. I never had it apart. I do now, lol. I dont think it was in there the whole time. I think it blew on me after the rebuild. I noticed there is no way this piece of bearing had enough room to float around the crankcase without jambing the motor up.

Okay cool! My thoughts were that you did the top end, and could have easily put the bottom end (in tack) in a parts washer and flushed out the crankcase while rotating the crank and give a good blow dry and made sure you didn't have any debris in there.

Also had you been flushing out the crankcase and rotating the crank while doing so, you may have noticed any roughness present that would indicate a bigger problem.

Checking end play on the rod may have revieled your problem as well. Anyway friend, I hope all goes well with the new rebuild, and that you can get back to riding sooner that later!

 

[DirtyJoe]

Alittle update.

I havent got REAL far, but I did order a new crank/rod setup.

Now, I need to either get the cylinder bored out or a new one is in order.

Im hoping to get it bored, just for the extra cc's, but if not, no biggy either.

I beleive theres enough there to bore, but I was told its not a sleeved head from the factory, so that my be a problem too.

Keep ya'll updated. I should be up and riding in a couple weeks either way

 

[JohnRaven.exe]

Good luck on the rebuild!!! :cool: I can't wait to get my bike back together! New top end and a rebuilt bottom end! Should run gooood after I'm done :laugh:

 

[ZeCatfish]

That cylinder is chrome plated, Nikasel you might be able to have it replated without plating. Since yhour going that far might look into a big bore kit.