Gas in transmission in 250R ATC

[ps2fixer]

Can you post a photo of it? I don't see anything in the part diagrams, but maybe someone with more experience with that model will recognize it.

[ironchop]

Ok, so the leak down test was done several times @ 8 psi for 10-15 minutes and it hasn't leaked even a tiny bit.

I noticed air coming out of the nipple on the case underneath the boot and reed while I was trying to pump up pressure, so this was plugged up temporarily with a hose, this may sound pretty silly...but what is this used for, and does it need to be sealed off?

Pretty sure that's the gearcase vent

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[ironchop]

This is the gearcase vent.... If there is air coming out when you pump it up and it's not plugged, then you do have an air leak and it's leaking into the gearcase.

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[rmcollector]

This is the gearcase vent.... If there is air coming out when you pump it up and it's not plugged, then you do have an air leak and it's leaking into the gearcase.

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Yes that is the nipple I am talking about, so where is your hose going to from that nipple? Does this mean my seals are leaking, or?

[ironchop]

Yes that is the nipple I am talking about, so where is your hose going to from that nipple? Does this mean my seals are leaking, or?

That hose goes out behind the motor and it's open to the ground. Normally it would have a T in it from the factory and one end goes up by the airbox and the other end is aimed toward the ground. That way it has two exits to vent the gear case in case one end becomes plugged up

Could be seals, that crack or hole I was talking about or the case half gasket is leaking

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[RoscoW]

I had that same gasket slip out of place on a rebuild once and it showed up on the leak down test. it does need to be unplugged for a proper test and if you loose pressure, spray soapy water on the suspected spots. Bubbles means an air leak. I suspect the gasket has slipped, they are very narrow in that area. Pull it apart, buy a new OEM centre gasket and lightly lap the case halves to get a flat mating surface......should be good to go.

Ross...

[rmcollector]

I had that same gasket slip out of place on a rebuild once and it showed up on the leak down test. it does need to be unplugged for a proper test and if you loose pressure, spray soapy water on the suspected spots. Bubbles means an air leak. I suspect the gasket has slipped, they are very narrow in that area. Pull it apart, buy a new OEM centre gasket and lightly lap the case halves to get a flat mating surface......should be good to go.

Ross...

Wouldn't the center case be bubbling when sprayed during the test if the gasket failed?

[ironchop]

Wouldn't the center case be bubbling when sprayed during the test if the gasket failed?

Not if the leak is in that red circled area in the diagram pic above. That part is inside the case where you can't see it

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[ironchop]

Here is where we think the leak is...

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[ironchop]

That gasket, the open area to the left is the crank case. The open area to the right is the gear case and that little sliver of gasket is all that keeps one sealed from the other

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[ps2fixer]

ironchop has all the images on this topic =).

I agree, looks like a crankcase vent (well transmission vent in this case since 2 stroke). As stated, there must be a gasket leak in the area I circled in read. Could be as simple as a deep scratch on the center crankcase sealing surface, or maybe a bit of old gasket material left over.

If you could remove the transmission section of the engine to get to the gasket surface, it would bubble where the leak is, but it's internal inside the engine. The fact it leaks out the transmission vent means it's getting into the transmission when it shouldn't be.

[Red Rider]

It could also be leaking forward of the crankcase into the counter-balancer cavity via the centercase gasket.

I had that same gasket slip out of place on a rebuild once and it showed up on the leak down test. it does need to be unplugged for a proper test and if you loose pressure, spray soapy water on the suspected spots. Bubbles means an air leak. I suspect the gasket has slipped, they are very narrow in that area. Pull it apart, buy a new OEM centre gasket and lightly lap the case halves to get a flat mating surface......should be good to go.

Ross...

I had the same issue after replacing my crankshaft a few years ago.

[rmcollector]

That gasket, the open area to the left is the crank case. The open area to the right is the gear case and that little sliver of gasket is all that keeps one sealed from the other

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Makes sense, thanks for showing me that. Ive done a few before, but was just trying to avoid splitting the cases. Would the crank seals cause this air to flow out of the nipple, or should my focus be on this gasket? When this nipple is plugged up, I get no drop in psi on the leak test, and of course, when the nipple is not sealed off I can't even get up to 5-10 psi because air is coming out of it too fast.

[ironchop]

It could also be leaking forward of the crankcase into the counter-balancer cavity via the centercase gasket.

I had the same issue after replacing my crankshaft a few years ago.

I never thought of that until you mentioned it. Thanks for pointing that out!

Yeah, RM Collector.. what he said^^^

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[ironchop]

Makes sense, thanks for showing me that. Ive done a few before, but was just trying to avoid splitting the cases. Would the crank seals cause this air to flow out of the nipple, or should my focus be on this gasket? When this nipple is plugged up, I get no drop in psi on the leak test, and of course, when the nipple is not sealed off I can't even get up to 5-10 psi because air is coming out of it too fast.

Yeah it can leak thru the right seal and get in the gearcase via the clutch area or from the left seal into the counterbalancer and then into the clutch area and into the gearcase

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