Do I need to vent the left side stator case?

I was just wondering if I need to vent the stator cover. I have seen the vents listed for sale for the xr650r but I didn't think much about it until I pulled off the cover just the other day to rewind my stator. I noticed a little bit of oil in the bottom of the case and I was wondering if that is just normal bypass or perhaps there is something more to it. The bike only has 250 miles on it but this is the first time I have had it off to adjust valves/upgrade my stator. Any thoughts??? :)

Have you ever taken a milk jug and filled it with hot water, poured it back out, and screwed the cap on? the jug shrinks up as a vacuum is formed inside. That is what is claimed is happening inside that cover when it gets hot and you suddenly cool it off from a water crossing or whatever. The fix is a small vent hose that is routed to the airbox or someplace secure.

The hose is cheap and the locating of the hose looks simple enough, but I've been watchin' this site for a couple of years and haven't noticed anybody experience this failure. I guess if it makes you feel good go for it.

Ive never thought about venting that case. What is the issue? Why would it need to be, or not be, ventilated? Is the vacuum Dutch mentions prone to sucking water in when ya go over a stream? I imagine a small amount of air now gets in there between the wires-at least enough to keep it atmospheric? But not sure. I've got many thousands of miles on my pig-and have had several coils on there. Cover must have been off 10 times. Never seen anything. No oil, water, dust. Nuttin. But i am a desert guy-so maybe in the woods its a different ball game.

Just curious-who offers the vents?

The issue is around the oil seal and any pressure that would cause the seal to leak into the cavity. I didn't think it was much of an issue since I haven't heard much said about it except I have seen the vents for sale on the SRC website. What made me wonder was finding a little bit of oil in the case when I pulled it off to do some service work. I was wondering if in fact it is an issue to be aware of or just a fluke....

I have found oil in there too but haven't vented it yet.

Here is what SRC says about it:

Special tip: The area occupied by rotor, flywheel and stator in the XR-650R is a sealed cavity. This cavity becomes pressurized when the engine warms up to operating temperature. The gasket is not designed to withstand the pressure buildup created by the temperature rise. This gasket can be forced out due to the increased internal pressure or sucked in if a hot bike is suddenly plunged into water such as when crossing a creek. With the gasket dislodged and not forming a seal, water and or dirt can enter this chamber unbeknownst to the operator. If the gasket does not fail then the crankshaft seal can fail due to pressure and vacuum created. Any oil in this cavity is proof of this occurring. Over time water, dirt and oil can disrupt the ignition circuit. A simple solution is to vent the magneto case cover.

SRC offers a 3 foot piece of very small Teflon tubing that can threaded through the wiring harness and grommet in place of or beside one of the wires in the grommet. The other end of the tubing should be inserted into the air-box between the carburetor and air filter.

I know that excessive crankcase pressure has blown out many countershaft seals. That leads me to think that pressure from the back of the crank seal behind the stator could cause oil to leak into that area as apposed to vacuum from the stator cover. One of the first things I did with my bike was to check the routing of the crank vent hose.

I've come to the conclusion that a little bit of oil in the stator case might be normal for some bikes. It's a sealed system, but the heat and pressure causes a bit of oil to ooze past the seal over time. My bike originally had a little bit of oil inside the case too, but I've never seen more than a tea spoon of oil inside the few bikes I've opened up, but I suppose a bike could 'potentially' build up enough pressure inside the case to where it could be a serious problem. I simply bought some small teflon tubing with a diameter size similar to the spray tube that comes with a can of WD40 and routed this tube inside the stator wiring harness. I ran the teflon tube from inside the stator case inside the wiring harness, through the rubber wire harness grommet (I drilled a small hole throuh it), continuing through the wiring harness and had it exit the wire harness sheath underneath the seat and vent into the airbox. It's simple and inexpensive to do and I've never seen another drop of oil inside my stator case since then. Maybe the oil was in there to begin with and maybe my stator case would have stayed perfectly dry for the last two years even without the mod, but it was quick, inexpensive and simple to do. You can buy small teflon tubing from many places. $10 should buy enough tubing to do a bunch of bikes. Here's just one of many places that sells teflon tubing, but you can probably find it at your local industrial hardware supplier.


How do you know all this stuff??? Discount teflon tube dealers....!


I wanted to see what qadsan had to say about this. He's the man. :D I read all I could about this bike before I bought one and didn't see anything on this. It's a simple enough mod that I will do in the near future. :)

Thank you guys for the thoughts. Good information!! :)

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