06 YZ450 @ 240hrs cylinder looks good but should I replace it anyways?

I have a 06 YZ450 that has 240hrs on it. I pulled the engine apart even though she still ran like a champ and noticed that the cylinder still looks like new.:cheers: It still had the cross hatch, with a few minor wear lines that came right out with one quick hone, and no blow by from the piston. Can I still run the same cylinder with a new OEM piston or should I replace it? I also checked the crank and it looks good as well. I am going to do the crank, crank bearings and seals, piston kit and timing chain but was wondering about the cylinder. The head still looks good and the valves were still in spec. Any input is appreciated. Thanks!:moon:

Damn thats impressive what did you do as far as maintenance? What motor oil and filter did you run? What about air filter oil?

Everything sounds within spec, so why would you replace it?

Everything sounds within spec, so why would you replace it?

I agree, if it is within spec there is no reason to replace it.

i would have the cylinder measured (micced). remember that a cylinder is going to wear more front to back than side to side. you could see a crosshatch on either side and still be out of spec from front to back. i have a hard time believing a jug with that much time on shows almost no wear. imagine a big egg in your cylinder . thats an exaggerated view of how a cylinder wears. ....less wear on the top and bottom, more wear toward the center.

As far as maintance is concerned, I cleaned the no toil air filter after every ride and oiled with notoil oil, changed the Amsoil 20w50 after every other ride and stock oil filter every three rides. I only had to adjust one intake valve after break in and changed the timing chain already once as a peace of mind thing. I was asking about replacement because I was not sure how many hours one cylinder could take before the plating would wear off. I have seen cylinders that had the plating start to peel off.

i have a hard time believing a jug with that much time on shows almost no wear. imagine a big egg in your cylinder . thats an exaggerated view of how a cylinder wears. ....less wear on the top and bottom, more wear toward the center.

I have a cylinder dial bore gauge and I measured it 3 times in disbelief and it is still in spec. I also installed a hour meter when I brought the bike home from the dealer.

There are primarily two things that will render the cylinder unusable: Wear in excess of the limits (.002") and scratches that go through the Nikasil plating. The most wear will normally occur at the top of the range of the ring travel. A "shadow" there that doesn't hone out in a couple of passes needs to be carefully measured. Likewise, scratches that don't hone out quickly need to be evaluated with a critical eye.

Absent any of these, comparing the bore diameter (or piston clearance) at the extreme ends of the bore to several points in the middle of it will tell the story.

Thanks everyone for the input!

I'm impressed, I was hoping they would hold up as good as the 426's, what fuel do you run?

I run 91 from the 76 station.

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