03 kx 125 piston pin falls out-big mess!!

[cactusreid]

Can anyone help me solve why a ring retainer pin would come loose/and fall out?at least this appears to be what happened to my son's 125. I don't have it completely apart yet,so I'm not 100 % sure. we were riding at a harescrambles type track and the bike just quit mid track. yes the piston is almost a year old,but there were no signs of anything getting worn or noisy. jetting is 35 pilot,400 main,needle on #2 clip position. we ride about 1100-4000 ft altitude. plug looks safely rich all across the rpm range.also it appear to have put a pretty good verticial scratch in the cylinder wall at about the pin area.I'm assumeing the nicasil is ruined now. I have punched out and resleeved with iron inserts on kawis before,but I have no experience with replateing the nicasil cylinders. would this maybe a good time to do a big bore on the bike? are they done with a insert or a new larger cylinder as a replacement?what size could I go to in cc's? Info and suggestions are greatly appreciated. thks cactusreid

 

[Studboy]

Usually circlips fail because of improper installation, but you could have had something else. It sounds like it's time for a E.G. 144 kit!

 

[bclapham]

a 125 piston is only really good for 10 hours, any longer you are just kidding yourself and asking for trouble (which sadly you got)

the good news is that you can get back on the road quite cheaply- send the whole lot to Eric Gorr- he will bore, port and plate the cylinder for a bigger piston- either 133 or 144 CCs

 

[cactusreid]

studboy-from what i can tell so far it was the tiny little alignment pin for the ring that decided to leave the scene.I'm just trying to figure out why this little guy would fall out.

 

[Studboy]

Oh.... I see know, you aren't talking about the piston pin! (As I sit here and feel retarded!)

Usually they fail because the piston was left in service for too long.

 

[Micahdawg]

I have heard horror stories of wiseco ring locating pins falling out. This never kept me from using wiseco, but it has been in the back of my mind and I consequently inspect the little guys when i get a new piston. The way the ring gaps are cut though....there is a full shroud of ring that covers the pin. So even if the pin were to loosen up, the only way I can see it falling out is if there is enough slop (wear) on the piston and rings to allow significant movement. At this point I would think you would have piston slap and some other issues as well.

Micah

 

[yzrulz]

Micahdawg I had one of those such horror stories about a year and a half ago with my 02 YZ125. The pin didn't actually fall out, it pushed in allowing the ring to rotate around until it got to the exhaust port and popped out, the bike immediately quit as it stuck the ring and lost compression. I ended having to have the cylinder replated as the ring put quit a few scratches in the cylinder. I would think the hole that is drilled to hold the pin that keeps the ring from rotating should only be drilled as deep as necessary but this particular piston certainly was drilled too deep and wiseco wouldn't do a thing about it either!! They told me that all their 2-stroke pistons are drilled like that!!!!

 

[cactusreid]

It turns out that a sizable piece of the nikasil chipped off at the side of the exhaust port and beat it's way around inside. It took out everything in there! while I'm in there I'll put a rod kit in as well as piston and a new sleeve pressed in.

 

[Studboy]

cactusreid, I honestly WOULD NOT go the new sleeve route on that bike. I would replate and do a bigbore. You will be ahead in the long run.

 

[jmossbarger]

Ring locating pins fall out from fatigue of the piston. If the piston has been heat cycled enough, it will lose it hardness, which coincides to its ability to keep a pin in the piston. The pins are installed with a press fit, but after a while, it loosens up, and this is what you get. As the one guy mentioned, it is possible for a ring pin to go into the piston, this is not because the hole was drilled too deep, the pin actually can plow into the aluminum. Once the hardness is out of the piston from excessive heat or exceeding the service life, the aluminum is like butter and the pin can just push into it. Does it suck? Yes, but with proper tuning and service, it doesn't happen.

Good luck,
Joe

 

[Jaybird]

Bruce,
Don't you think a ring change (coupled with accross the board measuring & inspection) at 10 hours would be sufficient, rather than a whole top end?

I realize that many folks keep things in service longer than they should, but only 10 hours on any top-shelf piston seems a bit overkill.

 

[viking20]

I also think a lot of guys , do just like the really fast riders , change a 125 piston after 5 , 8 or 10 hours...Keep in mind that the last bit of speed these guys are able to run at puts a lot more stress on everything.
My son is not a star of any kind , but he is certainly fast enough on his 125 to break parts....I change the ring after about 10-12 hours , and the piston after 20-25 hours , and we have no problems.
IMO , its important to use at least 33-1 premix on a hard ridden 125 or smaller bike.....
Running a whole year on the same piston is asking for trouble IMO...

 

[2-Strokes 4-ever]

I had the same issue with an RM125 (Suzuki's piston). And the top-end was brand new! Very important to check ring gap and adjust accordingly before installation. (Slide new ring into cylinder and measure gap.) I wasted cylinder and had to re-sleeve. I am happy with steel sleeve...(no plating) as it can be over-bored, and wiseco offers over-bore pistons. Have gotten MANY hours with very little cylinder wear.

 

[Micahdawg]

Wonder why Wiseco can't add the ring pin to their forging rather than press it in afterward. The whole point of a wiseco forged piston is increased strength....no point in having a super strong piston if something as small as a pin falling out can cause big damage.

MIcah

 

[Studboy]

Micah,

VERY FEW people who have run the pistons within their service limits (or even beyond) have experienced the pin falling out. Wiseco has a good quality product IMO, I will continue to use them.

 

[bclapham]

Bruce,
Don't you think a ring change (coupled with accross the board measuring & inspection) at 10 hours would be sufficient, rather than a whole top end?

I realize that many folks keep things in service longer than they should, but only 10 hours on any top-shelf piston seems a bit overkill.

Jay- you are correct. 10hours is overkill, but the 144 pistons i was using from eric were so cheap it was just as quick and easy to throw a new top end in. I would even reuse the base gasket quite often.

But saying that, those were race hours and that bike did a lot of work pulling a 220lbs vet up the Glen Helen mountains each week!!

However, ive measured pistons that were OK around the circumfrence, but i did notice the ring grooves would get a little loose- i wonder if that was the case here?

 

[viking20]

I have seen these pins fall out on most popular brands of pistons over here , I think its just a matter of bad luck....
I dont think they can get around setting a pin in after machining the piston. Because of the almost identical bore and stroke between brands , the core is probably the same for several bikes , and the pin is probably located differently because of the ports.
Bruce , I have noticed the size of the piston is often within spec , even though the part has a lot of hours of use.
A well used piston mic´ed to the exact same size as a new one , even when used with a new ring , often dont give the same " feel " as a new piston......Dont know if the worn piston expand as much as a new one ?
Dont be fooled by apperance or measurements , and keep running an already old piston , suddenly it gets very expensive , even though the piston looked fine.