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Discussion Starter #1
Just changed the piston on my 250f. Fired it up ran for about 2 mins,everything fine then turned it off. Went back to put the rest of the bits on after a couple of days and fired it up again and now its smoking like a chimney!! Whats happened? Is it a strip down again, I,m thinking so but what am i looking for?
 

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Did you put the rings the correct way up?
What ring gap did you set them to?
Are you sure you did not break the oil ring? Was it multi piece ring or one piece KTM ring?
 

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Discussion Starter #3
3 piece oil ring, what ring gap? whats that then? vertex piston. Which way up? one ring on the top, then a thin ring above and below the spring type ring. The spring/oil ring did seem rather bigger than it should of been. could not get it to sit in with the other 2 thin rings.bit of a struggle. Just took the head off, bore seems ok, but ran out of light to see. To be honest I thought it would be just a straight swop. Did,nt know about setting ring gap and wot not.
 

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doesn,t show fitting the oil ring which is the problem. but thanks cos i did,nt know about the measuring.
I posted that link to show that the rings fit in the bore AND STILL HAVE A GAP BETWEEN THE ENDS

There is supposed to be a gap between the ends of the spring ring before trying to fit the scrapers onto the shoulders of the spring ring. It aso shows how to orientate the 'ring gaps' around the bore which i thought might be helpfull

I think you'd better buy a manual
 

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Ring gap
You need to fit the ring in the bore about 40mm down from the top. Set it level by poking the piston down. Measure the gap with a feeler gauge. Gap of a new ring should be 0.1mm for every inch of bore.

Marks on rings always indicate the top of the ring.

Three pice rings have a springy middle bit that is fitted first, with the ends touching not overlapping. It will feel like its too big, but its not! Then the skinny rings go each side. Stagger the gaps in the rings so gas cant get past. No marks to indicate top. These style rings are best fitted through the top of the barrel using a piston ring compressor. Oil the inside of the compressor and tighten it onto the piston to squeeze the rings, then put the piston in the barrel and tap the compressor till its sitting flush on the top of the barrel. Then tap the piston into the barrel.

Tap the piston down until its only just enough out to fit the pin through it. A mm or two more and the ring will pop out!!

Fit the circlips with the gap at the top.
 

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Discussion Starter #8
I,ve got a manual, but didn't see about ring gaps.I,ve fitted it as you said Kev, but must admit the spring ring is a right pain to fit. The problem I had was trying to compress the spring without damaging it as it did seem too big, when i compressed by hand it overlapped itself, will have a look this morning and see what the crack is, thanks, you,ve been a big help.
 
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