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YZ250 Head O-ring Stretch

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I'm doing a top end on my 2016 YZ250, and when I pulled the head off, I noticed the red inner O-ring popped out and was nowhere near being able to fit back into the groove if I needed it to.  I've not seen this O-ring so stretched before.  What causes this, and should I be concerned?

yz250-head-oring.jpg

Edit to add: Yes I know the wash looks rich - you try keeping up with conditions in Colorado!

Edited by Tankslap

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I would say the heat makes it stretch. I recommend that they be changed anyway after 10 or so hours if you pulled the head.

Edited by 2 STROKE YZ DOC
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29 minutes ago, 2 STROKE YZ DOC said:

I would say the heat makes it stretch. I recommend that they be changed anyway after 10 or so hours.

Is that amount of stretch abnormal?  That thing must have been waiting to jump out of the groove for quite some time.  And these O-rings have a lot of moto/track hours on them.  Been very lazy this last summer.

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52 minutes ago, THE KRAN said:

They are supposed to do that.

The heat makes them expand and seal better.

 

Thanks for the reassurance.  I just don't remember it being that drastic the last two times I had the head off.

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On 10/10/2018 at 11:07 PM, Tankslap said:

Is that amount of stretch abnormal?  That thing must have been waiting to jump out of the groove for quite some time.  And these O-rings have a lot of moto/track hours on them.  Been very lazy this last summer.

That one is one of the larger expansions I have seen. Usually just a 1/4" out of the loop on most engines I have opened up. 

Edited by 2 STROKE YZ DOC
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I had the opposite problem, a brand new one from a gasket kit, I think it was Cometic, would not fit, it was too large and kept getting pinched.

 

I had to reuse the one that was in there.

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Viton and silicone o rings grow when exposed to chemicals in contact cleaner and or gasoline.

Not made to grow with heat.

Later George

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1 hour ago, Hick said:

I had the opposite problem, a brand new one from a gasket kit, I think it was Cometic, would not fit, it was too large and kept getting pinched.

 

I had to reuse the one that was in there.

That can happen with OEM as well. They can be just a tiny bit to big for the groove but if you keep working around it, and then sliding the head on and wiggle, it will drop in and seat. Done that a few times with new ones.

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If you lightly coat the O-ring with grease that will glue it down and hold it in the groove for assembly. The manual even shows to grease it.

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7 hours ago, Kinger317 said:

If you lightly coat the O-ring with grease that will glue it down and hold it in the groove for assembly. The manual even shows to grease it.

I do that to all of mine on reassembly . 

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I've never had any issues with putting new ones in, but then again I only buy OEM for anything related to the engine.  Costs a tad more, but peace of mind goes a long way.

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28 minutes ago, dirtyclods said:

Your engine loves you.....it laid carbon build up in the shape of a heart ❤.

looks more like Straya (Australia) to me! The arrow is even spot on the north most point!

Edited by eXc
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