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New OEM cyl and wiseco piston

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I recently bought a brand new OEM cylinder for my 00 YZ250 and a Wiseco piston along with some gaskets on ebay for a good deal.

Can I just throw in the wiseco or do I need to hone the cylinder for proper clearance?

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He said its a wiseco piston so is one size only. Just put it in and run bike in as usual. No need to hone as it will be already done from factory ready to go:-)

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You will need to check your ring end gap, that is about it.

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Agreed. Besides you are not suposed to hone those cylinders except to clean the glase from a used cylinder. Like you said, it's a new OEM cylinder so just check the ring gap, put it together and ride.

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Yeah I figured it would be ok I just wanted to make sure. I've read that wiseco pistons need more clearance than cast, so wasn't sure if it was ok to use in a new cylinder.

I always check ring end gap.

Anyone ever seen a new OEM cylinder? Are the ports chamfered? These ones are and I'm not sure if the factory did it or if the previous owner did. Hmm?

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OEM ports are chamfered but it's minimal and it's not always done that well.

I've seen OEM ports that showed evidence of snagging a ring because they weren't camfered properly.

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Brandnew? What letter does it have?

They come normally in A, B, C and D sizes. Differences are small and tiny but a brandnew A cylinder I'd start with an A piston.

+1

Yamaha makes 4 pistons for that year bike each with slightly different sizes. The service manual says to purchase a piston with the same letter designation as the cylinder. I can't think of any reason not to follow this advise. Having the perfect piston to cylinder clearance will insure you get proper lubrication and not too much piston slap.

Here is an excerpt from the Yamaha manual for my 125. Assume the 250 is similar.

____________________________________________________________________

When you purchase a cylinder, you cannot designate

its size. Choose the piston that matches

the above chart.

Piston clearance:

Standard <Limit>

0.040~0.045 mm 0.1 mm

(0.0016~0.0018 in) (0.004 in)

Cylinder mark a Cylinder size

A

54.000~54.002 mm

(2.1260~2.1261 in)

B

54.004~54.006 mm

(2.1261~2.1262 in)

C

54.008~54.010 mm

(2.1263~2.1264 in)

D

54.012~54.014 mm

(2.1265~2.1265 in)

Piston mark a (color) Piston size

A (red)

53.957~53.960 mm

(2.1243~2.1244 in)

B (orange)

53.961~53.964 mm

(2.1244~2.1246 in)

C (green)

53.965~53.968 mm

(2.1246~2.1247 in)

D (purple)

53.969~53.972 mm

(2.1248~2.1249 in)

Cylinder mark Piston mark (color)

A A (red)

B B (orange)

C C (green)

D D (purple)

Edited by rjpjnk

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+1

Yamaha makes 4 pistons for that year bike each with slightly different sizes. The service manual says to purchase a piston with the same letter designation as the cylinder. I can't think of any reason not to follow this advise. Having the perfect piston to cylinder clearance will insure you get proper lubrication and not too much piston slap.

Here is an excerpt from the Yamaha manual for my 125. Assume the 250 is similar.

You do realize the title has "Wiseco" piston right? As in, one size fits all. Although you are correct for using a cast oem piston, it doesn't do the OP any good.

To OP: I had my cylinder replated to spec and purchased a new wiseco. Rings were already gapped to Wiseco's recommendations so I just had to drop in the pison and gaskets and off I went.

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Yeap the tittle says new OEM cylinder and wiseco piston. With a brandnew cylinder I would not use a wiseco piston. But that is me.

He also said something about the previous owner so it might not be a sparkling brandnew cylinder.

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You do realize the title has "Wiseco" piston right? As in, one size fits all. Although you are correct for using a cast oem piston, it doesn't do the OP any good.

To OP: I had my cylinder replated to spec and purchased a new wiseco. Rings were already gapped to Wiseco's recommendations so I just had to drop in the pison and gaskets and off I went.

Yes, I guess I should have been clearer. I'm suggesting he not use the wiseco, put it back on ebay and get the matched OEM.

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I don't know why you wouldn't use the Wiseco piston, you just follow the same procedures for re-assembly as you would for a used cylinder setting up with the recommended clearances.

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I use weisco pistons in new OEM and millinium replated cylinders. Check the end gap if it's in spec you are good to go. I do however use Vertex in my KTM's just silly I guess

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