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Broken Ceramic on a two stroke spark plug?


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I let a buddy ride my 99 yz 125 and he went down a path and he said it stalled. I thought he fouled a plug so I took it out and there is a chunk of ceramic missing. It felt like the crank was tight so i pushed it back to the truck and now that the motor has cooled it is locked up. I am just going to rebuild the top and bottom end, but what do you think caused it. The gas was mixed right so it wasn't that. 

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How many hours on the crank and top end? Could have just been its time to go, it is 16 years old. The other possibilities could be jetting, poor air filter maintenance. You'll find out when you take it apart.

OEM crank

Vertex top end

That's what I'd do...

It had a wiseco crank it it so it hasn't had the same crank all its life. The jetting and air filter are both correct and it isn't crank seals because it would idle 

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It had a wiseco crank it it so it hasn't had the same crank all its life. The jetting and air filter are both correct and it isn't crank seals because it would idle

By correct for the air filter you mean clean? It's colder now, did you re-jet for cooler temps?

Wiseco cranks are garbage.

You asked what would be the best crank rebuild and top end, the OEM crank is generally the highest quality, I use Vertex pistons, also high quality.

I never mentioned crank seals.

Edited by poldies4
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