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YZ250F Big Bore?

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I have heard of problems getting the head gasket to seal, anyone else heard of these failures?

Should I go with 12:1 JE or 13:1 Wiseco for an additional $50?

How much jetting change is required?

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Is that thru Luke's racing? He had a kit where he installed a ring on the cylinder to help seal the head gasket but when I went to purchase that kit he was out of them so I ended up getting the Athena kit. Head gasket failure is 75% caused by lack of preparation. Make sure the head is clean and flat. Make sure cylinder is clean and flat and make sure the base is clean and flat.

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And replace the head bolts. They are cheap and good insurance. Check the head surface by wet sanding it lightly with a piece of emery paper taped to a thick piece of glass or marble.

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Oh and proper torque procedures for the head bolts is a major factor as well. As far as compression goes you'll probably not notice a difference between the two. What size kit are you looking at?

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my freind runs the 290 athena kit,never had any head gasket issues,i did a stealth 269 kit,and my head gaskets always leaked by the 10 hour mark.i would just go with the athena,it seems to work well.i think his jetting was stock except the main jet was dropped from a 180 to a 175.

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my freind runs the 290 athena kit,never had any head gasket issues,i did a stealth 269 kit,and my head gaskets always leaked by the 10 hour mark.i would just go with the athena,it seems to work well.i think his jetting was stock except the main jet was dropped from a 180 to a 175.

I have 140 hrs on Cylinder Works 269 kit and I've never had a single problem. When the BB went in, I also had it ported and HotCams put in and then re-jetted on a dyno. The main jet went all the way down to a #160.

I absolutely love the set-up.

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The 12:1 piston is a 2 compression ring piston, and the 13:1 is a single compression ring piston.

I have run a couple different pistons in my motor and the 2 ring pistons have held up a hell of a lot better/longer than the single ring pistons.

At 40 hours the single ring pistons were done, the skirts were starting to wreck the cylinder from rocking, the 2 ring pistons I could put in new rings and go 20-40 more hours before the same damage would occur.

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