Stihl MS261C - oil pump?

[KWood255]

Hi all, I have a 4-5 year old MS261CM which I bought new. This fall I noticed the chain was tightening on its own. As it turns out the bar is not getting any oil, which I did not immediately notice. 

I used some compressed air to blow back the oil delivery system in case of a blockage...nothing. I changed the worm gear today, although the original looked perfect. Still nothing. I cleaned out the bar oil reservoir, sprayed out with brake cleaner and found no obstructions. 

Any ideas? Oil pump itself shot perhaps? Can't be many more options that I'm aware of...? Thanks 

[barbender]

 May sound obvious, but did you clean out the oil hole through to the bar rail? Sometimes it will get plugged. I take a torch tip cleaner, or something else small like that (in fact I just broke the tiny screwdriver on my Leatherman yesterday cleaning the bar groove and oil hole on my bar for my firewood processor) and make sure the hole is clear all the way through, so you can see light through it.

[KWood255]

Hi Barbender, yes I did. I started with the basics here, but nothing yet. I understand it's quite rare for the oil pump to fail on these, but that's about my last resort. 

[barbender]

Up here in the frozen north, the saw shops will often get a run of stripped oil pumps after the first good cold snap (below 0F). Guys will have summer weight bar oil in the saw and it takes the pump out because it's too thick to pump. 

[chet]

When you blew air though the system did you notice it blowing into the oil tank. If not you may want to check the screen for ice up.

[PoginyHill]

I had a similar issue on mine. Replaced the pump with no change. Ended up being the "arm" that drives the pump. I can't recall the details, but the arm was dragging such that it wasn't turning with the engaged clutch as it should. So when the chain was running, the pump was not. To add to my bad memory, I can't recall (probably never could figure out) why the arm was bend or whatever it was such that it was dragging where it shouldn't have been. Hard to envision that happening on its own - but that's not normally something I take apart, unless I took the clutch off for some other reason.

[KWood255]

Thanks for all your replies fellas. Yesterday I removed the pump. As soon as I took the rubber oil supply line off the pump, oil began to run. When I removed the pump, I spun the drive shaft and watched small amounts of oil being pumped out of the output side. I sprayed the ports out with brake cleaner and compressed air really well, as well as the oils supply port to the bar. Reassembled and it works perfectly. I can only assume there was an obstruction within the intake side of the pump...? 

On another note, I was thinking the worst and needed an excuse for a new saw. While I picked up a few parts I also bought a new MS400C. Haven't ran it yet, as the 261 is back.