Can I run a Wiesco piston in a “C” size cylinder on a 2017 yz12

Michaelh1001
Edited Date/Time 6/22/2022 11:20am
The bike has around 35-40 hours and mainly trail ridden, and it’s only showing about 120 compression so I ordered a Wiesco piston (https://www.royaldistributing.com/wiseco-piston-kit-yamaha-063102.html) I’m not totally sure if it will fit or if I have to get the matching letter.

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JohnCharlesC 6/20/2022 3:49pm
6/20/2022 3:49pm
If this is the bikes first top end from the factory, you have a "B" size piston in your picture.

A = Red Inner Gasket
B = Orange Inner Gasket
C = Green Inner Gasket
D = Purple Inner Gasket
1
Michaelh1001 6/20/2022 6:04pm
6/20/2022 6:04pm
JohnCharlesC wrote:
If this is the bikes first top end from the factory, you have a "B" size piston in your picture. A = Red Inner Gasket B...
If this is the bikes first top end from the factory, you have a "B" size piston in your picture.

A = Red Inner Gasket
B = Orange Inner Gasket
C = Green Inner Gasket
D = Purple Inner Gasket
I understand that, but will the piston be good for its first top end, the link https://www.royaldistributing.com/wiseco-piston-kit-yamaha-063102.html.
Skerby
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Skerby 6/21/2022 7:55am
6/21/2022 7:55am
The difference between an A and D cylinder is .0005"

This is why I think yamaha just sells a single piston size in the kits.

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Moto520
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Moto520 6/21/2022 8:02am
6/21/2022 8:02am
I would buy the matching size. You could get away with an "A" piston in a "C" cylinder and i'm sure you'd be fine. I'm just particular about my bikes so that's what i do.
1
JohnCharlesC 6/21/2022 8:30am
6/21/2022 8:30am
JohnCharlesC wrote:
If this is the bikes first top end from the factory, you have a "B" size piston in your picture. A = Red Inner Gasket B...
If this is the bikes first top end from the factory, you have a "B" size piston in your picture.

A = Red Inner Gasket
B = Orange Inner Gasket
C = Green Inner Gasket
D = Purple Inner Gasket
Michaelh1001 wrote:
I understand that, but will the piston be good for its first top end, the link https://www.royaldistributing.com/wiseco-piston-kit-yamaha-063102.html.
Wiseco's website shows that it should fit 2005-2019.

Part No. 845M05400

https://powersports.wiseco.com/wiseco-powersports-yamaha-yz125-05-19-pr…
Falcon
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Falcon 6/22/2022 11:19am
6/22/2022 11:19am Edited Date/Time 6/22/2022 11:20am
JohnCharlesC wrote:
If this is the bikes first top end from the factory, you have a "B" size piston in your picture. A = Red Inner Gasket B...
If this is the bikes first top end from the factory, you have a "B" size piston in your picture.

A = Red Inner Gasket
B = Orange Inner Gasket
C = Green Inner Gasket
D = Purple Inner Gasket
Just FYI, I don't think you are correct about this. I've owned 7 YZ125s and 2 YZ250s since 1997, and every last one of them had a red inner O-Ring.
The colors you are referring to are inked on the respective A-D pistons, though.

EDIT: (Not all my bikes were "A" cylinders. My current YZ250 has a "B.")
JohnCharlesC 6/22/2022 11:42am
6/22/2022 11:42am
JohnCharlesC wrote:
If this is the bikes first top end from the factory, you have a "B" size piston in your picture. A = Red Inner Gasket B...
If this is the bikes first top end from the factory, you have a "B" size piston in your picture.

A = Red Inner Gasket
B = Orange Inner Gasket
C = Green Inner Gasket
D = Purple Inner Gasket
Falcon wrote:
Just FYI, I don't think you are correct about this. I've owned 7 YZ125s and 2 YZ250s since 1997, and every last one of them had...
Just FYI, I don't think you are correct about this. I've owned 7 YZ125s and 2 YZ250s since 1997, and every last one of them had a red inner O-Ring.
The colors you are referring to are inked on the respective A-D pistons, though.

EDIT: (Not all my bikes were "A" cylinders. My current YZ250 has a "B.")
What I meant was, the picture he posted shows a "B" piston in the cylinder, since its from the factory and has the Orange inner gasket, not "C" as his title states.

If it were a "C" piston the inner gasket would be Green.

mwilcox349 6/22/2022 3:17pm
6/22/2022 3:17pm
JohnCharlesC wrote:
If this is the bikes first top end from the factory, you have a "B" size piston in your picture. A = Red Inner Gasket B...
If this is the bikes first top end from the factory, you have a "B" size piston in your picture.

A = Red Inner Gasket
B = Orange Inner Gasket
C = Green Inner Gasket
D = Purple Inner Gasket
Falcon wrote:
Just FYI, I don't think you are correct about this. I've owned 7 YZ125s and 2 YZ250s since 1997, and every last one of them had...
Just FYI, I don't think you are correct about this. I've owned 7 YZ125s and 2 YZ250s since 1997, and every last one of them had a red inner O-Ring.
The colors you are referring to are inked on the respective A-D pistons, though.

EDIT: (Not all my bikes were "A" cylinders. My current YZ250 has a "B.")
JohnCharlesC wrote:
What I meant was, the picture he posted shows a "B" piston in the cylinder, since its from the factory and has the Orange inner gasket...
What I meant was, the picture he posted shows a "B" piston in the cylinder, since its from the factory and has the Orange inner gasket, not "C" as his title states.

If it were a "C" piston the inner gasket would be Green.

I've never seen anything but an orange inner oring gasket on all the YZ125s and 250s i've owned. Even in the oem top end gasket kits Yamaha sells, always orange. Also never heard that a different colored oring dictates what size the cylinder is.

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