Question about 2002 Yamaha YZ 426 F

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Water leak/mixing with oil

Heya i have a prob with water leaking out past the gear select shaft on my 1987 yz 125 also the water is mixing with oil in gearbox i have drained oil and is milky what are my options

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Change the seal behind the water pump impeller
the shifter shaft seal will stop leaking
if it continues to mix water and oil you will have to change the head gasket

Posted on Apr 13, 2009


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Hi there I pour water in to my radiator on my ktm 125 sx 2007 and the water comes out the middle of my gear box casings and of course it's mixed with the oil. Any ideas was thinking inner water pump...

Your cooling system leaks into the engine. You need to check the water pump for damaged oil/water separator and cylinder's head gasket next.


Feb 05, 2012 | 2007 KTM 125 SX

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2004 YZ 250 is leaking fluid out of the hole just behind water pump underneath the crankcase. The gasket looks fine and its not leaking from the gasket its actually coming out of the hole. I started...

The hole is a weep hole, designed to drain coolant from water pump seal leakage or oil from bearing seal leakage from contaminating either system. So one of the seals is leaking, and you should rebuild the pump.
Looking at the parts diagram it appears the impeller is threaded onto the shaft on the YZ250....hope that helps, heres the parts diagram

Mar 06, 2011 | 2004 Yamaha YZ 250

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I'm getting fuel in the crankcase oil of my 1994 YZ 125

Unless I am mistaken, (Honda guy myself, not fully up to date on mid to late 90's Yamaha) it is a 2 stroke so fuel air mix runs through the crankcase anyway but, excessive amounts are usually caused by a stuck needle valve in the carb. If it is getting into the gearbox oil then you probably have a bad crank shaft seal which requires major surgery.

Good luck hope this helps.

Mar 26, 2010 | 2003 Yamaha YZ 125

1 Answer

Leaking oil from power valve on 2000 yz 125

It is normal for the powervalves to leak, but it does depend on where it is leaking from.

The hose on the left side is the power valve chamber vent - it is normal for it to leak thick black oil from this hose.

If the leak is on the right side, and the oil is transmission fluid, then the seal on the actuator shaft needs to be replaced.

Excessive oil from the powervalve hose is a possible sign that the compression is low. Low compression equals lower exhaust temperatures and this can lead to incomplete combustion.

Jan 27, 2010 | 2004 Yamaha YZ 125

1 Answer

Engine problem

Water coming out of the hole is to indicate that the pump seals need to be replaced. Some water is probably in the gearbox now. If the oil is whiteish you do. Pull the right case cover then remove the pump cover and the impeller then replace the seals. Remove the liquid gasket so that the hole is open again. You can see a parts diagram at Click on the red "OEM PARTS" tab. Items 6 and 7 are the seals separating the water from the oil. Put a wrench on the impeller shaft next to the gear, then unscrew the impeller as if it were a screw. It would be good to replace the gasket (item 10) as well. Please take a moment and rate my answer to your problem.

Jan 03, 2010 | 2003 Yamaha YZ 125

1 Answer

What is the easiest way to change my shifter shaft on a 1999 yz 125... i put that my bike was a 2003 because they didnt have the option of a 1999...

Remove gearlever,drain gearbox oil,drain coolant,remove powervalve actuator cover,place small allen key in slot provided & remove bolt on actuator,remove radiator to waterpump hoses,remove clutch cover,slide shaft out from left to right,(If clutch hub is in the way remove clutch assembly),fit new shaft ,reassemble,replace gearbox oil & coolant & bobs ya uncle.

Nov 16, 2009 | 2003 Yamaha YZ 125

3 Answers

Leaking both oil and a mixture of oil and water

well when you have water and oil both leaking it most of the time means a head gasket or in your case a jug gasket

May 25, 2009 | 2004 Yamaha YZ 250

1 Answer


The impeller screws onto the impeller shaft. Go to the site below and you can see a parts diagram. You will select the brand, year, model, etc... It has the part numbers and prices.

There are actually two seals. Are you sure the leak is a bad seal and not the water pump gasket or a cracked/broken housing cover?

Please post a top rating for this solution. Thanks! :)

May 19, 2009 | 2004 Yamaha YZ 125

3 Answers

2001 yz125 grey milky tranmittion oil

stick your cok down the petrol hole

May 05, 2009 | 2003 Yamaha YZ 125

1 Answer

What oil for yz 125?

I would use maxima mt 75w gear oil in all 2-stroke trans.

May 01, 2009 | 2003 Yamaha YZ 125

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