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bg10459

Crankshaft Primary Drive Gear???? PLEASE Help!!

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I'm rebuilding my 02 YZ250 and I have a question about the thrust washer that goes under the primary drive gear on the right side crankshaft. (#2 in this diagram -> http://shop.thumpertalk.com/oem.asp?partcategory=52665&manufacturer=6&category=3&year=2002&model=1291). The manual (and the linked diagram) clearly show that the thrust washer goes first, followed by big gear, small gear, washer and bolt. The problem I see is the thrust washer is splined like the crankshaft, but there is a slot in the crank where the thrust washer sits where there is no spline which would allow it to move off center. Is this the way it's supposed to be? or am I missing something? When I spin the crank, I can already see the thrust washer isn't perfectly concentric, and I would imagine it would only get worse when the engine revs.

I'm certain the fine folks here can help me, so I express my gratitude in advance :thumbsup:.

Edited by bg10459

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I don't remember having an issue with this.

Maybe this pic will help.

Good luck !

IMG_6176.jpg

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The problem I see is the thrust washer is splined like the crankshaft, but there is a slot in the crank where the thrust washer sits where there is no spline which would allow it to move off center. Is this the way it's supposed to be?

Yeap that is correct.

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I'm rebuilding my 02 YZ250 and I have a question about the thrust washer that goes under the primary drive gear on the right side crankshaft. (#2 in this diagram -> http://shop.thumpertalk.com/oem.asp?partcategory=52665&manufacturer=6&category=3&year=2002&model=1291). The manual (and the linked diagram) clearly show that the thrust washer goes first, followed by big gear, small gear, washer and bolt. The problem I see is the thrust washer is splined like the crankshaft, but there is a slot in the crank where the thrust washer sits where there is no spline which would allow it to move off center. Is this the way it's supposed to be? or am I missing something? When I spin the crank, I can already see the thrust washer isn't perfectly concentric, and I would imagine it would only get worse when the engine revs. I'm certain the fine folks here can help me, so I express my gratitude in advance :smirk:.

That is correct, just put it in and forget about it

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I went around and round with the same thing when putting my bike back together after installing the WR trans. I was very careful to keep everything together just as it came apart during the tear down so I knew that's how it came from Yamaha but it still didn't look right.

...

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Well, I did just put it together and all is well almost two years and many many miles later...

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My son and I just ran into this same issue on his 02 250. IMHO, this design sucks I was thinking of adding a plump O-Ring under the ring to keep it centered and "balance" it out. Does anybody else think that's a good idea or foresee any problems from doing that?

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When I spin the crank, I can already see the thrust washer isn't perfectly concentric, and I would imagine it would only get worse when the engine revs.

I put a hotrods crank in my bike about 15 hours ago. Long story short, I've been searching for answers as to why I have more vibration than a new crank should. I spoke with my friend who rebuilt the engine and he says he was sure that the crank runout was in-spec. He advised that I check the primary drive bolt was tight, which I did about 10 hours ago.

Long story short, my primary gear bolt came loose on Sunday and tore a hole in the inner clutch cover. :rant:

I never turned the primary gear to check that this washer was centered, but I wonder if this runout could have caused the vibration and eventual loosening of the bolt.

If anyone has an inner clutch cover for sale, please let me know.

And if you have experience with repairing the threads in the crank ... I've ordered a new bolt, but the threads were very smashed on the bolt.

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Hi

I am dealing with the same problem now ! Bike left me stranded in the middle of nowhere! Putting it tigether and I observed the same thing . The splined washed just dis not look right just sitting there off center and loose . 

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From a 'mechanical sympathy' perspective, I really hate this design.  You've got it assembled correctly, it's just wierd.

From an engineering perspective, there's absolutely nothing wrong with it.  It's just a spacer and is so lightweight and small diameter that the imbalance is imperceptible.  

As to the bolts working out - lots of loctite and torque to spec.  It's a known issue with that bolt, but if you're careful assembling, you won't have a problem.

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