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2005 yz250f cylinder is it good or bad?

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Took apart the top end on my bike everything looked in nice condition, the cylinder is pretty smooth no gauges or deep marks but was wondering what the 2 white marks are at the very top of cylinder. really not in the budget to get a new one but if that's the case guess I will have too I just bought a new standard top end to rebuild the bike today. also the valves had allot of carbon on them is there a way to clean that off the exhaust ones had pretty thick carbon on them. ill add pics of the valves later or tomorrow.

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Not sure just got the piston and rings today I will try and measure them in the next couple days.

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Marks look typical, not unusual.  You will notice a slight ridge at the top where those marks are.  They are from the rings where the piston stops at TDC.  They may have a slight ridge compared to the rest of the cylinder.  We usually run a hone around the cylinder for 2-5 turns to rough it up and provide a surface for new rings to seat in, moving it up and down as we go so we get the normal hash mark pattern for oil to move thru.  It may take another turn or two to bring those marks down a little at the top. Then we use a Scotchbrite pad to clean the cylinder out afterwards.  Should be a simple build back.  Good luck.

PS.  As long as the plating has not come off the cylinder and the piston clearance is within spec, you're good to go.

Edited by ronbuell

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I went the safe and faster route and just ordered a new standard cylinder. I started rebuilding last night so far put the new timing chain in.

I bought a standard size weisceo piston but have a question it comes with the oil expander ring and the two rings that go on each side of that then there is a bronze color compression ring and another compression ring (that color is the same as the 2 small oil rings that go around the oil expander ring greyish/black) I am trying to confirm that the bronze color ring goes on the top of piston? and also there's marks on each of the rings they should always face up correct?

 

I can post pics if needed thanks

Edited by ktmnj

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Writing or any marks up.  Pretty sure the "bronze" ring will be in the middle with the lighter color - almost aluminum color will be up top.  I just did rings on a TTR-230 last week and this was very confusing in the service manual.  I found a few top end rebuild youtubes and went with what was provided in the video.

Don't forget to "clock" the rings.

I am surprised that you found wiseco to be cheaper than OEM.

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thanks for the response

the second pic is the rings I'm confused on the ring to the left is the blackish ring which looks square on the edges and the ring on the right is the bronze ring and has a tapered angle edge.

I went with weisco at the time because I had credit towards the purchase already.

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So in the second pic the ring on the left is the middle compression ring and the copper color with chrome edges is the top compression ring. I keep getting different answers I think you are correct because that's what I thought also

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Just found a section in my TTR-230 manual.  The Scraper ring is goes in the middle with the thinnest edge of the taper pointing up.  I am assuming this position would be the same on the YZ.

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thanks, I put the copper color ring with silver edge on the top place and the black on in the middle. I seen a lot of pics and a you tube video of the guy doing the same,

last question if anyone can help assembled the whole motor and today I couldn't figure the timing marks out on the fly wheel there is a m shape by it self then a h and a straight line right next to each other. how do I find tdc? I assume you line the line up the the flywheel line right? pretty sure my first try the timing was wrong.

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Center of the H is TDC. The H is the firing range if you need to advance or retard timing for some reason.

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okay I was lining it up with the straight line right next to the H, so the correct way would be line it up directly in the middle of the H and line the marks on the cams parallel with the top of head? thanks

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Correct with the chain tight on the exhaust cam side. Once you think you have it lined up slowly turn over by hand to ensure everything is smooth. You are almost there.

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thanks, my buddy has the manual for the 05 just have to get back over there for it if I need it. I did watch a you tube video and the guy lined it up with the I mark on the flywheel and parallel at the top of course. earleier that's what I did I think I was just one tooth off. what happens if I line it up with the I mark?

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I am assuming 04 and 05 will be the same.  Here is the snippet from the 04 manual on timing.  One way to confirm is to pull plug and put a plastic straw down it. As you turn the motor over you will see where TDC is and the corresponding mark on the flywheel.

 

 

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