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yz125 top end kit recommendations

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Im getting ready to replace the reeds and top end on my yz 125 because it has low compression. I want to find a top end kit that wont fail and is of good quality(preferably oem). I also want to make sure it is the exact right size so i can get the best results. Im having trouble finding a good kit that has the right size piston according the the stamp on my cylinder. does anyone know of a good kit to buy that wont give me any problems and is the right fit? And where can I find that stamp for the correct piston size?

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Yamaha offers A, B, C, & D sized pistons,

depending on how many hours your plating has and, the actual measured diameter

you can easily run one size larger letter piston than what the cylinder marking indicates.

Ideally don't rely on the stamp, measure the actual size.

 

If I remember correctly, the OEM 'piston kit' comes in a B size,

meaning for someone doing their 1st top end refresh on 

a brand new bike ('A' cylinder) that's what they'll get when ordering.

 

Currently my 2010 YZ125 has it's original 'A' cylinder and a 'C' sized piston installed. 

With 60-70 hours or so of use on the cylinder I'm on the 4th piston (very preventative replacements)

the original plating is still serviceable but for good measure likely due by the end of this season.

I'm just very careful on doing a gradual warm-up each time I ride.

Edited by mlatour
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8 hours ago, mlatour said:

Yamaha offers A, B, C, & D sized pistons,

depending on how many hours your plating has and, the actual measured diameter

you can easily run one size larger letter than what the cylinder marking indicates.

Ideally don't rely on the stamp, measure the actual size.

 

If I remember correctly, the OEM 'piston kit' comes in a B size,

meaning for someone doing a top end refresh after 20 hours on a brand new bike that's what they'll get.

 

Currently my 2010 YZ125 has a it's original 'A' cylinder and a 'C' sized piston installed. 

With 60-70 hours or so of use on the cylinder I'm on the 4th piston,

the original plating still serviceable but for good measure likely due by the end of this season.

I'm just very careful on doing a gradual warm-up each time I ride.

A good warm up and a clean air filter will extend your piston life.

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18 hours ago, mlatour said:

Yamaha offers A, B, C, & D sized pistons,

depending on how many hours your plating has and, the actual measured diameter

you can easily run one size larger letter piston than what the cylinder marking indicates.

Ideally don't rely on the stamp, measure the actual size.

 

If I remember correctly, the OEM 'piston kit' comes in a B size,

meaning for someone doing their 1st top end refresh on 

a brand new bike ('A' cylinder) that's what they'll get when ordering.

 

Currently my 2010 YZ125 has it's original 'A' cylinder and a 'C' sized piston installed. 

With 60-70 hours or so of use on the cylinder I'm on the 4th piston (very preventative replacements)

the original plating is still serviceable but for good measure likely due by the end of this season.

I'm just very careful on doing a gradual warm-up each time I ride.

 

18 hours ago, mlatour said:

Yamaha offers A, B, C, & D sized pistons,

depending on how many hours your plating has and, the actual measured diameter

you can easily run one size larger letter piston than what the cylinder marking indicates.

Ideally don't rely on the stamp, measure the actual size.

 

If I remember correctly, the OEM 'piston kit' comes in a B size,

meaning for someone doing their 1st top end refresh on 

a brand new bike ('A' cylinder) that's what they'll get when ordering.

 

Currently my 2010 YZ125 has it's original 'A' cylinder and a 'C' sized piston installed. 

With 60-70 hours or so of use on the cylinder I'm on the 4th piston (very preventative replacements)

the original plating is still serviceable but for good measure likely due by the end of this season.

I'm just very careful on doing a gradual warm-up each time I ride.

What should I do if the stamp on the cylinder is not there? I was looking for it but I think it got scrubbed off somehow.

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As mentioned, ideally you should have the cylinder's actual diameter measured.

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