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ring gap spec 05 yz250

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hi can anyone please tell me the ring end gap specs for an 05 yz250 i dont have a manual to check for myself thanks.

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0.40 - 0.55 mm (0.016 - 0.022 in)

The the FAQ thread or the thread arnego2 posted to download a factory service manual. You'll use it, a lot, trust me!

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The manual specs 0.016"-0.022", but most people recommend .004" per 1" of bore which would be 0.011" at a minimum.

I gapped mine at 0.016".

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Will you guys explain something to me, please. Wiseco sells one piston size for this bike as sort of a one size fits all. Great, no problem, and I do believe them. But why are the rings ALWAYS tight as compared to the factory manual spec? Either they are not, or wiseco makes them large.

And how big of a deal is this? Obviously too tight is no good, but what counts as too tight?

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Will you guys explain something to me, please. Wiseco sells one piston size for this bike as sort of a one size fits all. Great, no problem, and I do believe them. But why are the rings ALWAYS tight as compared to the factory manual spec? Either they are not, or wiseco makes them large.

And how big of a deal is this? Obviously too tight is no good, but what counts as too tight?

Wiseco suggests slightly tighter ring gap than Yamaha does, 0.040" gap per 1" of bore. On a YZ250 this works out to 0.0105" or 0.27 mm, considerably tighter than Yamaha.

Who's right? Probably Yamaha. Cylinder geometry and material will play a roll in the expansion, and maybe something about their design warrents a little larger gap. A trail engine may get away with a tighter setup, a dune bike that sees high piston & cylinder temps may need a little more gap.

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Wiseco suggests slightly tighter ring gap than Yamaha does, 0.040" gap per 1" of bore. On a YZ250 this works out to 0.0105" or 0.27 mm, considerably tighter than Yamaha.

.

Are you sure on that?

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Are you sure on that?

http://www.wiseco.com/PDFs/Manuals/RingEndGap.pdf

Opps, I forgot some zeros! Their table for dirtbikes suggests as a general guideline:

  • 0.0040" gap per 1" of bore for the top ring
  • 0.0050" gap per 1" of bore for the bottom ring

For the YZ250 that comes out to

  • 0.0105" top ring gap
  • 0.0131" bottom ring gap

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http://www.wiseco.com/PDFs/Manuals/RingEndGap.pdf

Opps, I forgot some zeros! Their table for dirtbikes suggests as a general guideline:

  • 0.0040" gap per 1" of bore for the top ring
  • 0.0050" gap per 1" of bore for the bottom ring

For the YZ250 that comes out to

  • 0.0105" top ring gap
  • 0.0131" bottom ring gap

I've never seen that pdf before, thanks.

I've also never heard of having different gaps for top and bottom ring. I just put a Wiseco in my bike, and they're instructions say .004 for every inch of bore, nothing about top or bottom. Both my rings were fatter than 0.013 but less than 0.014, so say 0.0135. That's the same gap I had on the last set and they saw 40 hours no problem.

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I've never seen that pdf before, thanks.

I've also never heard of having different gaps for top and bottom ring. I just put a Wiseco in my bike, and they're instructions say .004 for every inch of bore, nothing about top or bottom. Both my rings were fatter than 0.013 but less than 0.014, so say 0.0135. That's the same gap I had on the last set and they saw 40 hours no problem.

I just always set to factory minimum specs (unless the rings already have a larger gap new). Last set of Wiseco's one was spot on 0.016", the other was somewhere between 0.010-0.013", so I opened it up to 0.016". Always have done top ends this way.

They say the larger bottom gap helps to fight ring flutter on the top ring.

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I just always set to factory minimum specs (unless the rings already have a larger gap new). Last set of Wiseco's one was spot on 0.016", the other was somewhere between 0.010-0.013", so I opened it up to 0.016". Always have done top ends this way.

They say the larger bottom gap helps to fight ring flutter on the top ring.

Ring flutter? I've never heard of that before.

I've never touched my rings for fear of leaving burrs or not cutting them square.

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