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I'm can't complain about my bad luck any longer !!

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When I'm wrenching on a bike, I tend to have the stupidest, crappiest things happen to me. From stripping the crap out of a bolt to installing something incorrectly, or forgetting to install something and having to do the job twice. Well, if I was saving all my good luck for one instance; I'm glad it was this one !!

I bought my 2005 YZ 250 last summer. The previous owner only rode it for a season and a half before converting to a four stroke. When the previous owner replaced the original top end, he opted for the 68.5mm Wiseco piston and thus had the cylinder bored and replated to a larger diameter. When I purchased the bike, the owner says he had only about 10 hours on the top end with the over-sized piston. I know how that story goes from people trying to sell you bikes. I decided to replace the top end this summer so I could get a base-line for compression and have the peace of mind of a fresh top end and an idea of when the next top end will need to be done.

After I disassembled the top end, honed, de-carboned and cleaned all the parts, I stayed up late last night to re-install the power valve. I figured I'll put the cylinder and piston on the following morning. When I pulled the left and right side exhaust valves, I didn't pay attention to which side I pulled them from. I checked the manual and it said nothing about a difference between the left and right side valves. So, I assembled the power valve and everything seems to operate well, then I head off to bed. I lay awake because something bothers me about those left and right exhaust valves. I kept thinking, am I sure there isn't a specific left vs. right side. All of a sudden I remember that one side of each valve is rounded. Why are they rounded? I get out of bed and head back to the garage. I noticed as I look down in the cylinder, the left and right side exhaust valves actually protrude into the cylinder. HOLY HELL, then it hits me!! This is an over-sized bore and the exhaust valves had to be trimmed back so they don't protrude into the bore. I pull everything apart and sure as hell, I needed to rotate each valve 180 degrees so the rounded part was facing the inside of the cylinder which prevents them from protruding into the bore.

I was a mere few hours of sleep away from installing my brand new piston into that cylinder with the exhaust valves installed incorrectly. Had this been a standard bore, it wouldn't have mattered how I installed those left and right side exhaust valves. Without a doubt, my top end would have made an ugly sound and gone BOOM :) . I still can't believe I caught that in time. Something made me take a look at it again, even thought my original idea was the wrong train of thought; at least it made me look at it again.

It will be a long time before I have the right to piss and moan about my bad luck. Anyway, when I did a compression test (before I ever started the engine), I maxed out at 225. Should I have broken in the top end by starting it before I did a compression test? In any event, does that reading sound about right, even for a larger bore? It started on the second kick and idled perfectly for the first 5 minute heat-up cycle. Tomorrow morning I'll complete the break-in cycles.

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When I'm wrenching on a bike, I tend to have the stupidest, crappiest things happen to me. From stripping the crap out of a bolt to installing something incorrectly, or forgetting to install something and having to do the job twice. Well, if I was saving all my good luck for one instance; I'm glad it was this one !!

I bought my 2005 YZ 250 last summer. The previous owner only rode it for a season and a half before converting to a four stroke. When the previous owner replaced the original top end, he opted for the 68.5mm Wiseco piston and thus had the cylinder bored and replated to a larger diameter. When I purchased the bike, the owner says he had only about 10 hours on the top end with the over-sized piston. I know how that story goes from people trying to sell you bikes. I decided to replace the top end this summer so I could get a base-line for compression and have the peace of mind of a fresh top end and an idea of when the next top end will need to be done.

After I disassembled the top end, honed, de-carboned and cleaned all the parts, I stayed up late last night to re-install the power valve. I figured I'll put the cylinder and piston on the following morning. When I pulled the left and right side exhaust valves, I didn't pay attention to which side I pulled them from. I checked the manual and it said nothing about a difference between the left and right side valves. So, I assembled the power valve and everything seems to operate well, then I head off to bed. I lay awake because something bothers me about those left and right exhaust valves. I kept thinking, am I sure there isn't a specific left vs. right side. All of a sudden I remember that one side of each valve is rounded. Why are they rounded? I get out of bed and head back to the garage. I noticed as I look down in the cylinder, the left and right side exhaust valves actually protrude into the cylinder. HOLY HELL, then it hits me!! This is an over-sized bore and the exhaust valves had to be trimmed back so they don't protrude into the bore. I pull everything apart and sure as hell, I needed to rotate each valve 180 degrees so the rounded part was facing the inside of the cylinder which prevents them from protruding into the bore.

I was a mere few hours of sleep away from installing my brand new piston into that cylinder with the exhaust valves installed incorrectly. Had this been a standard bore, it wouldn't have mattered how I installed those left and right side exhaust valves. Without a doubt, my top end would have made an ugly sound and gone BOOM :) . I still can't believe I caught that in time. Something made me take a look at it again, even thought my original idea was the wrong train of thought; at least it made me look at it again.

It will be a long time before I have the right to piss and moan about my bad luck. Anyway, when I did a compression test (before I ever started the engine), I maxed out at 225. Should I have broken in the top end by starting it before I did a compression test? In any event, does that reading sound about right, even for a larger bore? It started on the second kick and idled perfectly for the first 5 minute heat-up cycle. Tomorrow morning I'll complete the break-in cycles.

thats a true dirtbike rider, eat sleep, and think about bikes,.......... Good save, enjoy:thumbsup:

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thats a true dirtbike rider, eat sleep, and think about bikes,.......... Good save, enjoy:thumbsup:

Forgot about dreaming about bikes.:D

That was a close one. I have a Clymer book and it says to keep the power valves marked for right and left. :)

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What years does your manual pertain to? I installed the valves on both sides to see if there was a noticeable difference, but I couldn't see any. On Yamaha-Motor.com the parts fiche shows the same part number for both the left and right side valves. The bike started fine and made no crunching noises, so I assume all is well.

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Whenever I do something like you just did, something brilliant and awesome, that makes me feel very smart and pleased with myself, I find a way to do something so dumb and brainless within the next ten minutes that it just leaves me speechless. You'll see. There's something your going to smack your head on, or a hammer your going to bang your fingers with. Life imitates art, and by art of course, I mean The Three Stooges.

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Whenever I do something like you just did, something brilliant and awesome, that makes me feel very smart and pleased with myself, I find a way to do something so dumb and brainless within the next ten minutes that it just leaves me speechless. You'll see. There's something your going to smack you head on, or a hammer your going to bang your fingers with. Life imitates art, and by art of course, I mean The Three Stooges.

LOL, true . . . true !! It may not be today, but probably within the next couple of days I'll make up for my luck and brilliance by doing something so utterly dumb, it defies logic. Now excuse me while I go dry my hair while taking a hot bubble bath.

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What years does your manual pertain to? I installed the valves on both sides to see if there was a noticeable difference, but I couldn't see any. On Yamaha-Motor.com the parts fiche shows the same part number for both the left and right side valves. The bike started fine and made no crunching noises, so I assume all is well.

The parts were modified to fit the new bore, making them different.

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What years does your manual pertain to? I installed the valves on both sides to see if there was a noticeable difference, but I couldn't see any. On Yamaha-Motor.com the parts fiche shows the same part number for both the left and right side valves. The bike started fine and made no crunching noises, so I assume all is well.

Its a 94-01 book. I rarely open it or even look at it.

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