chainsaws leaking oil

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I believe the valve is two way. Let's air in and out, but not liquids.
I could be wrong though as I have never bothered to take a vent apart.
I can say when I have had issues it was with dirt caked older saws.
The only saw I currently have is an MS260 and it doesnt leak a drop, despite being stored in my shed that gets pretty hot. I have never cleaned the vent on it either, but have always kept it clean. It's a bit of a cherry that really only cuts a few cord per year and an odd tree job or three.
 
During the colder weather I keep a chain saw warm in the house. I noticed it ended up near the radiator. It was leaking bar oil. I keep it on cardboard folded over. I figured out the heat was making the oil flow. I hand no bar on it. I moved it to a cooler spot it stopped leaking. Go figure.
 
I thought the vent was one way... Only supposed to let air in not pressure out...

The check is one way in, so the pressure builds up due to daytime heat, & forces the oil out through the pump to the bar port.

A very good thermal pump, if left outside in the sun, plus it keeps the bed of your truck from ever rusting, lol.
 
I'd start by degreasing the whole works and removing the flywheel and coil. Then fill the tank up and see if you can figure out where its leaking. Could be just the cap..or not.
So, today I took the saw apart a bit today. Took the recoil cover off, the ignition coil out, but I couldn't get the flywheel off for everything I tried short of building a puller to use. But I degreased everything I could get to, and blew it out with compressed air. What's the coil gap? I used a piece of cardboard from a lightbulb box as a spacer to set the coil. Maybe a little bit thicker than a business card. Saw ran pretty good. Was thinking about doing a muffler mod to it.
 
Automotive stores, O'Reilly and Napa sells a dye that you can put little bit in oil and when it leads you can use a black light and look for the glow in thelight for locating the source of the oil leak.

I've never used dye leak on a chainsaw but it would be a option if a visual could not locate the leak.
You can review the dye on-line. Their are more than one dye type, some is for anti-freeze leak, some for motor oil, some for transmission oil etc. (at about $12)


Do not leave the dye on a surface where it's leaked for very long or you cannot remove the dye so as to check later if it's still leaking after repairs are attempted.

I left some dye from a AC refrigeration system on for about 3 days and after I repaired the leak the old dye was dried still in place and I could not tell if I had stopped the leak until I sprayed painted little bit of black matte Hi-heat fast dry paint over the dye and tested. The dye remover sold for such would not remove the old dried dye.
 
Ya, I have the AC dye. But if you look at the pic in post 34, it's pretty clear where the oil came from. There was a lot of small debris on the oring and the sealing surface where the cap sits. I haven't put the new caps on, but the saw doesn't seem to be leaking. I cleaned up the saw in degreaser and ran it for a bit. Seems to be working ok.
 
I have to keep a heads up on them Stihl flippie caps. If you use your saws very much you will also most likely get a dose of gas or bar oil in your crotch from the cap falling off.:surprised3: Not a good feeling when way back in the woods on a hot day and gasoline in the crotch area. Thinking about taking a extra pair of britches.Maybe Stihl should start including a extra pair of britches with their saws that have the flippie caps.

Also you may know this, the AC dye you mentioned may not mix with bar oil.;):eek:
 
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