I need your guys opinions...............

[windowscleaning]

Ok, I am in the process of rebuilding my 96 kx 125 bored 80 over(134cc) and I have somewhat of a problem. I have spoke to 4 different local shops in my area and they have all told me something different. When I removed the head/jug, I noticed on the top of the piston on the outside edges quite a few 1/4 - 1/2 " slashes, like something small, such as a pin was hitting against the piston everytime it compressed. It did not do any damage to the cylinder walls at all, only the head of the piston and a couple small marks on the cooling head. This is what I was told:

1. Your wrist pin bearing is going bad and the pins are starting to fall out which is causing the the pin(s) to enter the head of the piston whenever the piston is in it lowest position and then escaping through the exhaust ports.

2. Since there was a 1998 piston (# 719m05600) in a 1996 motor most likely the piston rings are sliding up around the piston and making the inditations. Can someone tell me what the difference between piston # 719m05600 and # 652m05600?

3. The last time the motor or top end was rebuilt, something was dropped down into the top end before it was closed up.

Can someone please tell me if any of these explainations make any sense and if my piston is still useable or not? It has not started to eat away at the piston, it's just a few slash marks. If it is the wrist pin bearings, can they be changed or would I have to buy a entire new crank? What kind of other problems could have been caused by having a 1998 piston inside of a 1996 motor? Thanks in advance for any advise, Jason

 

[BigRedAF]

Hard to tell by the description.

I'm thinking a piston ring groove pin came out. If it was a wrist pin bearing you would've had a big failure. Another failure that will cause marks on the top of the piston is when the bridge on your spark plug breaks off. The bike will still run because the plug will spark to the side.

I'm thinking that if your talented enough to do a top end rebuild you would have noticed a plug failure. Check the piston ring groove.

 

[windowscleaning]

Just to make sure were on the same page, a piston ring groove pin is the groove in the piston that the gap in the ring sits around right?

 

[BigRedAF]

The PIN that the ring gap fits around. It prevents the rings on a 2 stroke from rotating and getting hung up in a port. That would trash your cylinder in a hurry.

 

[windowscleaning]

Ok, we were on the same page.....Would there be any marks or scrapes on the cylinder walls if that would have happened? It is just shocking to me that something has kinda torn up my piston but did not touch the cylinder walls! I am kinda new to this myself, so all your help is greatly appriciated, thanks

 

[BigRedAF]

It will generally damage the bore.

Occasionally crap will pass into the engine though the intake and get on top of the piston without damaging the bore. Your problem is puzzling but easy to figure out when you get it apart.

 

[IndyMX]

I wonder if it wasn't caused by detonation?

Do you have any CLEAR pics you can post?

 

[windowscleaning]

Well as I stated before, I do not see any damage to the bore at all....Is there anyway of posting pics on this site with a message? I would like to show you guys what I am speaking of so it will be a little better to understand.

 

[IndyMX]

Put in on someplace like Photobucket, and then post the link here. You have to be a subscriber to post pictures directly.

 

[BigRedAF]

The slashes description steers me away from detonation but it's hard to pick through this stuff. Pictures would be nice.

You can join (photobucket.com) for free and put all your pics there. Once you do that you can post the link here and we can see what your trying to describe.

There are are other ways but this one is fairly simple.

 

[windowscleaning]

Pic

Ok, I am trying to post a pic now....Let's see if it works! Ok it is stating that the file is too large, how do i change the size of the file?

 

[windowscleaning]

Ok I tried it with Photobucket, lets see if this helps!
And by the way this pic does not do the piston any justice....it looks worse than it really is....and that is a shadow around the outside edge...thanks for any assistance

 

[BigRedAF]

I'm thinking pin. I'm also betting on damage in that bore. If the pin came out and the ring rotated to a transfer port a small piece of ring could have broke off and made it's way to the top of the piston by way of the transfer port. If that's the case you will have damage at the bottom of the stroke and some scratches around the transfer ports.

The color of the piston doesn't point towards detonation and nether does that damage.

What does your spark plug look like?

Is the bridge missing?

The trash probably made it out through the exhaust port.

Is this still the 125 engine?

If so press on with the 134 project and all will be OK. You'll be getting a bore, re plate and complete top end piston kit with gaskets.

 

[BigRedAF]

I went to the Wiseco site and the 96 had 98 use different pistons. They're both the same bore so the change will be pin location, rings (one or two, thick or thin) or perhaps one is a flat top and the other a dome.

If the port configuration was the reason for the change then the pin placement would be different and the wrong piston would cause the rings to hang up. I haven't worked on a KX of your vintage so I can't be sure at this point.

Hopefully someone with KX history will chime in soon, good luck...

 

[windowscleaning]

This motor has already been bored @ 80 over, I have inspected the entire bore and have not noticed any scratches or hangup's....not even around the exhaust ports. I will see if I can get a few more pics posted here soon of the bore. I am not sure of what the spark plug looked like as I purchased the bike used and he just recently changed that out. Just my luck!! Thanks for all your help and trying to help me out, any other ideas or reccomndations are greatly appriciated.

 

[windowscleaning]

Tear Down

Alright, I just came from my local shop and we have completly tore down both cases and cannot find a single thing wrong!! There are 2 very small scuff marks on the bottom of the cylinder. Other than that we cannot find anything. Is there any other possibilitys of what this could have been caused by? When we completly removed the piston it was kinda hard to remove the ring as it was stuck in place (not sure if this is normal or not) but the ring gap pin was still in place also. Someone please help me, I dont want to put this motor back together and end up realizing there was a problem. Thanks again for all your help

 

[2strokerfun]

Somebody may have put it back in looking like that.
At any rate, piston is trashed.
Replace the piston, rings, wrist pin and wrist pin bearing.

 

[windowscleaning]

Ok, i have one other question....Even though I already have split the cases, is there anyway of cleaning down inside the crank cases without splitting the cases...The reason I ask is becasue I am not trying to spend another 80 bucks everytime i have to have the cases split.

 

[windowscleaning]

Bearing cage?????????

This is what I was just told, please tell me if it is true or even a possibilty. " there could be metal derbis coming from the bottom end since 2 strokes have suction from not only the top but the bottom as well, and the "main bearing cage" could be falling apart and entering the top of the piston. If this is happening can you tell which one of the main bearings it is?

 

[IndyMX]

If you have the cases split and the crank out, it won't hurt to replace both main bearings. Pretty cheap insurance at this point...

 

[whenfoxforks-ruled]

Your bottom end bearing is gone, it got sucked up through the transfers, compressed and then blown out the exhaust. If it is good, then it happened previously and they reused the old piston. Check the rod for up and down free play. Any and it is shot. Are the thrust washers left? Is the wrist pin area a pretty blue? And your head gasket looks like it got hot, make sure when you get the head fixed that they cut the surface. Or just buy a new one.

 

[BigRedAF]

Ok, i have one other question....Even though I already have split the cases, is there anyway of cleaning down inside the crank cases without splitting the cases...The reason I ask is because I am not trying to spend another 80 bucks every time i have to have the cases split.

An Old School way to clean out a bottom end at the race track so you can make the second moto is...

Say you sucked a ton of sand and you have the top end off. Pour a few cups of pre mixed fuel in the bottom end and rotate the crank with the rod quickly. After 10-15 seconds lay the bike over to dump out the crap and do it again.

Put a few drops of oil on the rod big end and put it back together. This is only a track side repair and not the proper way to fix your bike.

 

[whenfoxforks-ruled]

Big red, I do not call that one old school. That was before I actually took one apart, and seen what a tight little niche there is between the seals and main crank bearings. Also, when I realized there was this large magnetic thing on the left side, that pulled all the magnetic metals, not unlike what I was trying to wash out, to the left side! Since then I do not recommend even after a seizure on the top, not pulling the cases apart to inspect and clean. At worse, it will cost you the price of a complete gasket kit. Well worth the peace of mind!

 

[BigRedAF]

A saw Hannah's mechanic douche out his engine in the pits at the Astrodome in 1979 or 1980, it was the year he kicked Steve Wise's butt when Steve was on the black engine CR. He did as I said and through in a new piston. Start to finish was about 15 minutes. Hannah didn't miss the race. Of course back then you could just take off the pipe, four base nuts. loosen the carb and slide the top end off. No water and plenty of space to work in.

Like I said, it's not the proper way to do the job but it rinsed the dirt out of the bottom end and got him back in the game. I'm sure Keith did a complete overhaul Monday morning.

This was of course a two stroke and last time I checked the rotor/stator didn't magnetize dirt from within the cases.

 

[windowscleaning]

I have completly checked the crank and there is no up or down play which I figured was good and very minimal play in the side to side, I looked at the wrist pin bearing as well and it is not a blueish color, it actually looks brand new. Also, the thrust washers look excellent as well.....I am stumped of what this could have been caused by!!! And what do you mean by cutting the surface (of what) the gasket or the head? If it is the gasket I plan on replacing them all with new ones anyway after the rebuild.