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125sx leakdown


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After putting a piston in my buddies 125 sx last night we did a leakdown test and it failed miserably. The air is getting into the transmission somehow. Either through the case halves or the right side crank seal. I'm almost positive no air should be getting in the trans because that is how every other two stroke has been that i have worked on. I did however notice that there isn't a trans vent tube anywhere on the cases, and this led me to think that the trans may be vented to the crankcase somehow? I doubt it but I wanted to make sure before we split the cases. Thanks!

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Elaborate a bit more.

For instance:

How are you doing the leak down, where are you appling the pressure, how much pressure, and where are you stopping it up on the other end?

Do you have the PV side covers on and checking for trany leaks through the vent line on the R/H side cover or have that stopped up and checking through the fill hole?

One thought is, if you you have the pressure going through everything on the upper deck including the exhaust port out to the exhaust flange and you also have the PV side covers installed then the main PV and the auxiliary PV's will leak though the o-rings on the shafts and will go into the case/transmission? You can eliminete this as suspect by not having the side covers on while doing the check and if it is leaking there you can tell directly or by wetting the the area with WD-40 or somethign like that.. This would be normal to some degree and also depend on how tight the fit of the PV shafts into the head and weither you greased the shafts and o-rings or not.

Gary

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Elaborate a bit more.

For instance:

How are you doing the leak down, where are you appling the pressure, how much pressure, and where are you stopping it up on the other end?

Do you have the PV side covers on and checking for trany leaks through the vent line on the R/H side cover or have that stopped up and checking through the fill hole?

One thought is, if you you have the pressure going through everything on the upper deck including the exhaust port out to the exhaust flange and you also have the PV side covers installed then the main PV and the auxiliary PV's will leak though the o-rings on the shafts and will go into the case/transmission? You can eliminete this as suspect by not having the side covers on while doing the check and if it is leaking there you can tell directly or by wetting the the area with WD-40 or somethign like that.. This would be normal to some degree and also depend on how tight the fit of the PV shafts into the head and weither you greased the shafts and o-rings or not.

Gary

Thanks Gary,

I'm putting 8 psi into the intake boot, with the exhaust port blocked off with a plug. I wet the whole outside of the motor down with simple green and no bubbles. The powervalve vent line is plugged. I noticed the air coming out the clutch slave cylinder because we took that off to get the motor out so we did not have to bleed it. I put the cylinder back on and then took one of the bolts out and you could hear the air coming out.

Could you explain how the air from the powervalve could be leaking back into the trans? I can't see how that would happen unless it's going through the governor area in the case. We did not have any of those covers off and that might be a good place to look. We will have to check that out tonight!!!

Thanks again I appreciate the help. We're trying to ride tomorrow!

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Sorry, I was thinking about the big bikes (250/300) when I wrote that about the side covers, aux. PV valves, etc. so it was confusing I am sure.

I am not as familiar with the 125/200 PV setup and I don't think you have auxiliary PV's, but I am sure the PV still gets actuated by the centrifugal control unit (or governor) right? Which is in the trany right? Which runs off the water pump. Item's #66 & #67 move the PV. The PV area is open to, drains into, and is connected to the trany case/oil/clutch/water pump, etc. So, the concept of leaking from the exhaust to the trany is still valid and worth checking out before you split the cases. Of course it could also actually be leaking at the case split around the crank too.

Concept: The PV is in the exhaust stream where you are applying test pressure and its control shafts are sealed by o-rings to keep the exhaust gasses from going into the the spaces in the cylinder which drain (are connected) to the trany and the oil. You also still have a cover on the side of the cylinder, but I don't know if you can see the ends of the PV like you can on the big bikes or what you can see when you take it off. So, you have at least 2 o-rings #10 on the axle's for control #21 that separate your exhaust stream from the trany. I think. The o-rings keep oil out of the exhaust and exhaust out of the oil. If they are leaking you will be leaking pressure into, the trany from the exhaust.

Maybe someone more familiar with the 125/200 will step in and explain better.

The problem may be that there are not many folks that know what a pressure check is so your not getting a lot of responses in a short time.

I hope someone will step in that understands the 125 cylinder/PV configuration and explain exactly what and where. Maybe all this will help.

Gary

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Well Gary we determined it as a seal that rides on shaft #57 in your diagram that was leaking. In order to get a new seal, you must replace the whole cover which my buddy determined is too expensive at $125 so he is just going to run it. It isn't as bad as a crankseal leak, but it wouldn't give me piece of mind if I was relying on it to get me out of the woods haha.

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