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07 Ktm 250 Xc-w Rebuild Flop

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I had 72 hrs on original piston when I pulled it. Everything looked cherry. Ring gap was at .025 so I thought I'll put a new Wiseco piston kit in and buy an extra set of rings for the old perfect piston and save it for a backup.

I installed wisco piston kit #856M06640 including wrist pin, cir clips and rings (part #2614CD 66.40mm). Ring gap at 14-15. Lubed it all up and carefully put it together. Measurements all seemed perfectly in spec. Cycled the piston several times, used same fuel mixture as always and hot soaked the engine several times. And after 20 min or so of careful break in...oh shoot!!! What's that odd sound that increases as it gets hotter...and upon dis assembly found a terribly scored piston especially near the skirt end and chipped nikasil bore. How do you say...bummer hope to have this better:banghead: by race day Mar 29th.$$$

???? PS Does a 300xc head fit on the 250 xc-w? Answers or advise???

An upgrade may be an option or simply replate and go with the old piston and new rings for now.

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any idea what went wrong? Is it possible one of the rings wasn't seated or something. what a bummer.

fwiw, with ring gap of .025, i don't think I would have bothered replacing anything.

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Wow, that sucks! It would be nice to know what happened.....As for the head question, the guys at KTMTalk are who I'd go to. There's a bunch of guys over there swapping parts and the sort. Good luck!

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Thanks! I am recovering nicely from my extreme disappointment.

No one seems to understand why this happened. Looks heat related near the power valve but most of the scratches on the intake side. Wisco suspects lube problems but I used the same motorex mix and tank of gas from before. Rings look seated OK. When it heated up, piston possibly expanded and caused too much friction.

Cyl may have a crack and now may only be able to be sleeved and not plated. Wish I could put on a 300 but seems that head is 1mm too long in the stroke and the p. valve stuff is a little different.

Anyone have a good plated 250 cyl for sale for 07 ktm 250 xc-w???

I'll check the ktm site as well. Time is running out with Goldendale xc race in less than 3 weeks. I could use my old DRZ...OUCH. Good work out!

Coolest part of all was my bride of 20 yrs out helping me scrape gaskets last night at 9:30pm. I couldn't believe her support. I even took a picture! She rocks...$ is not so good now so she could have been kind of unhappy.

:p Just pay up$$$$$

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my weisco piston is doing well. I know some of their stuff is being made in China, saw a thread on ktmtalk about a recall on some yammy cranks and rods.

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The 300 head will not fit, to convert you would need the complete 300 top end. I hope you get her up and running. Do you know what your piston to wall clearance was? CJ

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sorry to hear about this,,,,

Are both the Wiseco and the stock pistons forged ? If not that may be your problem assuming you ran the same piston to bore clearance. If I remember my hot rodding correctly , the forged piston will expand more when hot.

I'm hoping to get close to 200 hrs before I tear my 300 down. I think 72 hrs may have been premature unless you're racing it all the time.

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sorry to hear about this,,,,

Are both the Wiseco and the stock pistons forged ? If not that may be your problem assuming you ran the same piston to bore clearance. If I remember my hot rodding correctly , the forged piston will expand more when hot.

I'm hoping to get close to 200 hrs before I tear my 300 down. I think 72 hrs may have been premature unless you're racing it all the time.

72 hours on a 300 is premature for most mortal men. :moon: The OP has a 250 though. I'm not certain how long they last although I'm sure 150 hrs. isn't outta the question. :p

The longevity of the 300 engine is one of the reasons I like it so much. :ride:

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The Wiseco pistons are#2's, meaning they are a little bigger than the original #1's that came stock. The #2's were designed to fit into a slightly worn cylinder.I can't imagine that in 72 hours you were worn down to needing a #2, but it certainly is possible. The forged Wiseco's expand faster than your stock piston, and expand faster than the cylinder.You can see where that can be big trouble.I've had good luck with Wiseco's in Japanese bikes, but not in KTM's.Some people have had good experience's, but not me.

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In the Jap bikes I've owned, I always used Wiseco pistons and never had a problem. In my KTM 300 I went with OEM. I heard of some issues with Wiseco in KTM's so I spent the extra money and went with OEM. On my 300, I'll get at leat 200 hours before I'll think about the next top end.

Tp me, it sounds like the piston expanded faster than the cylinder. Hope you her her back together without spending too much $.

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I'm hoping to get close to 200 hrs before I tear my 300 down. I think 72 hrs may have been premature unless you're racing it all the time.

I wouldn't even think about it before 200 hrs with your riding style.

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Just did the top end on my 08 250xc with about the same hours maybe alittle more, but its been though about 10 cross country races and at least double that for motocross practice. Put a domed type sx piston in it and now it smokes like crazy after the brake n. Checked the p valve while running and it seems to be working fine (those bikes are loud without a pipe on). Cant figure out why the excess smoke and it feels like a different bike. I just hope my main seal is not out :)

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So it's been six months and the new N West sleeve and wiseco piston rock. But to all KTM owners, stick with stock rings and pistons. I've had zero problems with the rebuild and will keep running the wiseco. Running first place in my class and finished all races this season but timed out at the Devil's Head ISDE in the Oregon XC OMRA series. I guess the forged and cast pistons swell with different tolerances and can totally hammer the Nic. plating.

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