Broken Piston on 250 EXC

[jc220]

Racing a HS this past weekend when my bike locked up on the second lap. Tore it apart last night and the top of piston was broken on the edge and piece of the ring had also broken off and become wedged between the piston and the cylinder wall. Needless to say the cylinder wall has a groove and will have to be fix not to mention new piston.

Has anyone else heard of the stroke pistons doing this. The bike is a 2002 and I have only had it less then 7 months. The plug looked good so it wasn't running lean (actually its always ran a little rich). I am just not sure what would have cause this.
Please help

 

[MikeS]

Dealer had a 02 250sx with the same thing happen..only 4 months old. It was raced by an agreesive A rider. I believe KTM helped out some but the guy had to pay for cylinder repair. Cause....overreved and leaned out causing it to detonate from the power to be at ktm.

goodluck

 

[ktmrandy]

Is this the 4 stroke? I have had the pinston pins that hold the rings in place fall out on my 300exc this allowed the rings to rotate and get stuck in the exhaust port and destroy the cylinder piston and exhaust valve.

 

[jc220]

No, it is the 2 stroke. Took the piston and jug back to the dealer this afternoon and he claims that dirt got sucked in the cylinder and wore out the rings to the point they came out of the groove and broke.

 

[SFO]

Can you post some images?
be worth 1000 words.

 

[DEANSFASTWAY]

Hey JC : Tell you what if the dirt went in the motorand broke the rings , you should be able to see where it getting in , ptobably was detonating and broke in the grooves . Was anything melted or burned away . Either way you better be sure that you check out the bootom end because that might cause your next walk back to the truck . You gotta have a lot of dirt to break the rings also the piston may look like it was sandblasted and may have like vertical marks from grit stuxck between it and the cyl bore . If the rings got so thinfrom time/use and needed replacement they cancock in the grooves and jam up .GOOD LUCK

 

[colorado-high]

I had the same problem with my bike and also know of two others with the same thing.The problem is that the end of the ring gets caught on the edge of the transfer port and the ring end gets stuck in the port and bends over and breaks the top of the piston.This is a problem that KTM knows about and will warrenty it.My bike was 7 months old with close to 4500 miles on it,the other bikes were 10 months and 9 months and all the repairs were covered under warrenty. The fix was to move the locating pin on the piston so the ring gap would not come in contact with the port.If your dealer will not cover it under warrenty you can ship the motor to my dealer and he will fix it under warrenty.

 

[proracer3]

If that is the answer your dealer gave you I would not go back there. I had the same thing happen and the dealer I bought my bike from said about the same thing (KTM WILL NOT WARRANTY) and told me the bike was lean. I talked to a friend of mine and he said he would call the dealer he gets bikes from and see what he thought. This dealer had heard of it and KTM was aware of the problem. I sent him all the old parts and he sent me all new parts including a new cyl. It only took about five days total and my bike was running again. It seems like alot of dealers are getting lazy. If you do not get this replaced for free give him a call he has a toll free number 877-389-7540. The dealers name is Fun Mart Cycle. Its worth a try because if I remember right it was aboud $750.00 for all new parts at retail.

 

[Anssi]

7 months is how many hours of riding? Have you replaced the piston or rings?

I sure wouldn't ride/race a 2-stroke 250 for seven months (that would be about 50 hours for me) without at least checking the top end.

 

[cujet]

Colorado-high, Are you the guy I met at the end of Sept? I was on a rented 4 wheeler, you were lounging under a makeshift shelter. If so, glad to hear you got the problem sorted out. how is the fouling plug problem???

Chris

 

[colorado-high]

cujet

That was not me.Mine seized in the middle of nowhere and took me seven hours of pushing, pulling and dragging to get back home.I probably have over 100 hours on the bike. I get a new one every year so I do not worry about doing top ends.

 

[dstktmusa]

If you have over 100 hours on a single cylinder 2-stroke KTM race engine per the 2003 owners manual, you should have checked piston/cylinder for wear 4 times.

 

[ml36]

ya, like the majority ktm owners follow that maintence schedule they put in the manual :silly:. other than the huge gouge in the cylinder from the ring, his cylinder still had excellent cross-hatches. his bike did not suck in dirt.

 

[jc220]

proracer3,
Thanks for the phone number. Called Fun Mart yesterday and they told me it was covered under warrenty and ordered me the new cylinder and piston that day. Said once he got my parts from me he would ship the new cylinder and piston. And just think, I was that close to being out $400.
I greatly appreciate the help guys. You saved the day.

The thing that made me the most upset about this whole situation is that my local dealer would even bother with calling KTM to check if they would fix it. I bought this bike from him and had to call a dealer 600 miles away that I have never bought anything from to get it fixed (the guys at Fun Mart Cycle rock).
Thanks again guys

 

[copyguy]

I now have a follow up question to this post. If you go out and replace all the parts is the piston going to break again? I'm assuming the replacements are stock 2002 parts. Colorado-high mention that the fix is to move the locating pin on the piston. I've never done this, what does it involve?

Since I have only about 350 miles on my bike I would like to do whatever to prevent the destruction of a cylinder and piston because it may take a year or two to have the problem and at that time I doubt my dealer will even discuss warranty.

Any feedback would be appreciated.

 

[jc220]

I am assuming KTM has got the problem lined out with the piston mfg and the locator pin on the replacement piston will be in the correct place. But I could be wrong.

 

[colorado-high]

The replacement parts(cylinder and piston)that I got were 03 parts.The locating pin was moved appo. 1mm further away from the transfer port than the 02 piston.

 

[dstktmusa]

The "new" piston has it's locating pin dead center at the bottom of the piston (if your looking down from the top) Before the locating pin was offset to the left side and was supported by the bridge between the ports in the cylinder. Colorado-high, check with your dealer about a Tech. Bulletin that KTM sent out regarding break in jetting for your 250. Install this jetting for the first tank or so. Thumbs up to KTM for standing behind their product on a 7 month old bike with a 30 day warranty!!!!!!!

 

[copyguy]

Do you think it would be enough to replace the piston with the 03 model piston or is the design change such that both the piston and cylinder would both have to be replaced?

Thanks

 

[old#48]

Does you guys know how far back in model years this "pin location" problem goes ?