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Yamaha yz250 hole between counter shaft

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Hello guys! I'm searching all over internet and can't find anything. What is that hole at picture? Why it's for? 

I'm asking because there is some little oil leak from there! 

Bike - yz250(4EW00) 2 stroke

IMG_1582.PNG

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it appears as though it is a breather for the gearbox  how is the oil level?? being a 2 stroke I wonder if a crankshaft seal is on its way out.

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That's located too low for a crankcase breather,

the actual location of the breather port is on the RH crankcase and appears in this parts diagram as #6 & #7 

link: https://www.partspitstop.com/oemparts/a/yam/5004374ef8700209bc78c4ab/crankcase

 

IMO the hole pictured is a sprocket guard mounting hole in which the threads have been stripped.

Simply re-tap the threads and insert a bolt and your leakage issues should be fixed.

Edited by mlatour

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not so sure about a sprocket cover seems to close to the output shaft and no mark from a bolt head. have you tried poking a stiff wire down the hole to see how deep it is (you should feel bumps on the side if it was threaded) and at the same time turn the gearbox over to feel if the wire touches a gear?? it maybe a machining hole that had a plug fitted to cap it off and the plug has fallen out. pic as an example.  do you have a workshop manual? it may show what is supposed to be there? just a thought.

machining hole bung 001.JPG

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