Exhaust Valve ''Breather''

A few months ago, I bought an '02 CR125 for cheap with a blown motor. The motor was taken apart and came in a box. Long story short, I got it running good as new. But, I noticed something I find kind of strange about the '02 model year.

This is the only model year CR125 that uses a breather hose for the power valve drain. All other years use a bolt that does not vent unless you remove the bolt. Looking at the OEM parts fiche, it shows a hose connected to a fitting in place of what would normally be a bolt on other model years.

It seems to me the power valve drain should be sealed by a bolt like all the other model years. When I was assembling the engine on my work bench, I did a pressure test with the OEM 2002 year breather fitting and hose connected. As soon as I pressurized the cylinder, the air blew right out the breather/drain hose. Seems to me this a nothing but an air leak...? So I installed a bolt and it holds air tight. The bike seems to run fine, but I am wondering if there is a reason the '02 bikes have a drain that is always open? Let me know what you guys think.

Click the link to see a picture of the OEM parts fiche. The OEM '02 parts are number 2 and 3. http://i88.photobucket.com/albums/k182/nathan89450r/02cr125exbreather.jpg


yamaha has all theirs and the older hondas just drip out a drain. if you have air coming through there, you should do a pressure test on the motor.

I think during a pressure test the crankcase pressure will bleed past the exhaust valve and into the gearbox, then out the breather. On engine assembly, some people goop up the power valve assembly with grease to minimize the effect. I've always plugged the gearbox breather during pressure tests, but maybe that's not proper procedure.

well if the crank is venting to the gearbox you have main seal issues.

not exactly what he is pointing at JJrace.

what he meant that pressure goes in thru the PV assebly of the cylinder part, goes under into the gearbox and out of the breather.

There is no air coming through the transmission vent line. When I did the pressure test, the only leak was coming from the exhaust valve drain tube. Which on any other year CR125 from the last 20 years is a screw. I don't get why Honda doesn't use a screw in the 2002 model... all the others do.

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