Yz 125

Craigyw1984
Edited Date/Time 3/28/2021 4:45am
Guys any advice would be much appreciated. Removed my piston to inspect, size and change ring. Is this normal piston wear for a 5 hr bike? I did expect more around exhaust bridge. Clearances all check out ok.


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DynoDan22
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DynoDan22 3/25/2021 10:32am
3/25/2021 10:32am
Is that a crack or a hair on the piston crown in the middle pic? What brand piston?
Craigyw1984 3/25/2021 12:29pm
3/25/2021 12:29pm
Took the jug off and cleaned it using scotchbrite. The mark is still there, so may possibly be cracked 😒. Im going to have machine shop size, hine and replace the piston. Found this in my expansion pipe, any ideas? Brass



FGR01
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FGR01 3/25/2021 1:23pm
3/25/2021 1:23pm
That brass piece looks like a pin out of a key lock or else a tip for some kind of tool?
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FGR01
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FGR01 3/25/2021 1:28pm
3/25/2021 1:28pm
Or a detent, like the on the takedown pins of an AR-15.

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Craigyw1984 3/26/2021 5:59am
3/26/2021 5:59am
Any ideas what Vertex cylinder clearance and ring end gap should be. Everyone i have contacted says different. May just go OEM and use Yamaha specs
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kb22
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kb22 3/26/2021 6:15am
3/26/2021 6:15am
I just went with a vertex and they don’t send that with the piston, refer to the tolerances set by the manual. Mine were listed as a measurable range.
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Craigyw1984 3/28/2021 4:33am
3/28/2021 4:33am
Piston sized and turns out i need a D sized fitted😕. Clearances actually working out at 3.5 thou. Bike had been plated and fitted with A size at the end of 2019. Very little use and this is required already? Vertex being fitted and referring to Yamaha specs as its a cast piston.
kb22
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kb22 3/28/2021 4:40am
3/28/2021 4:40am
That sounds like a lot of wear, where did you have it plated at and how many hours since?
Craigyw1984 3/28/2021 4:45am
3/28/2021 4:45am
I bought the bike with 5 hrs 😕. Plated in UK by reputable company. Sized with bore gauge. The vertex specifications are somewhat larger than Yamaha, although i have been told the Yamaha specs are what i should go by. Guys built race engines for years. I can only guess the engine has done more hours

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