Stihl 041 Farm Boss Oiling Problem

My bro-in-law has an old 041 Farm Boss his father bought new back in the 70s. Amazingly, the saw still has 145 psi compression and runs great. The problem is that he's hardly getting any oil to the bar/chain at all. The oil pump is held in by a snap-ring on the front of the saw. I removed it and it looks ok. I put air pressure to the tank and oil flowed freely into the pump bore. We reassembled the saw without the bar and chain and started it up. It takes a lot of RPMs to get oil to merely ooze out of the oil hole. I then thoroughly cleaned out the grooves/holes in the bar and re-installed with the chain. With the oiler turned all the way up, he's using less than 1/4 tank of oil per tank of fuel. The chain ends up being totally dry. Also of interest is that the oil holes in the bar end up totally clogged with debrie. Is this just because there's not enough oil flow to keep them open? Is it possible that the pump is just worn and weak? Got any ideas?

pump

Either the pump sring is collapsed, the oring is leaking, the rubber seal is leaking, the pickup screen is plugged, or the pickup hose is ripped.

Did the gear look straight across the teeth? They wear in the middle, then no longer mesh.
Also, is the pin from the sprocket to the worm gear still in one piece?

The rubber seal is fine, as the saw doesn't leak at all.

Do you have a schematic of the pump parts? To be honest, I don't remember the location of some of the parts you mentioned.

About the spring, if it's too weak, does this prevent the pump shaft from moving back and forth?

I did not check the hose or filter on the end. Sounds like a likely suspect. I'll be sure to check it out.

As Stihltech points out, the gear on the end is prone to wear. It should be straight - if here is a half moon in the middle (less diameter in the middle than both ends), it's probably not engaging with the worm drive.


Check that the pin drive (18) is in place... Often the cover washer that holds the pin gets damaged and the pin is missing, so just replace both if so.

I just took the thing apart again so that I can discuss this more inteligibly. The gear teeth are straight. The o-ring and seal are ok (no oil in the pump cavity and none leaking externally). The pickup tube and filter appear to be ok. What I've found is that the worm gear is not turning. What drives it? The pin #18? I've got the clutch off. Please explain how this works and disassembles.

Upon further fidling, the worm gear is out. The pin drive was the problem. The cover washer is fine but the pin drive is broken off flush with the end of the worm drive hole. Where in the world did the rest of it go? I don't see how it could get out. Can I just use a roll pin to replace it?

In the schematic, about part #s 2 and 4, which one is the o-ring and which one is the washer. I'm not sure which order they came out or where they go on the shaft. They didn't come out with the pump shaft.

Something to point out...

Most of ya'll will say I'm crazy, but here goes... Course I've got 2 of the 041's, so I'm a little familiar, but not expert with them. Mine was having the same problem with oiling not too long ago. I saved myself the pulling apart and asked a buddy of mine that's a small engine mechanic and works on saws all the time. HE said that a few times a year you should mix Kerosene with your oil to clean everything out. THIS IS JUST BAR OIL HE'S TALKING ABOUT... Nowhere else. He said that the kerosene mix with oil with thin it and clean out any deposits/clumps/whatever could be there from getting chips in the bar oil tank. I tried it with a tank, I prolly mixed it 3/4 oil to 1/4 kerosene, It worked like a champ. Since then I religiously do this every few months and have never had a problem since. Oilers for 041's are getting hard to find now also so it's better you keep them tip top and in clean operation. This worked for me, he says it works most times, not all the time. Anyhoot, before yanking everything apart next time, give'r a try and see your results. Hope this helps someone the way it did me...

As mentioned above, the problem was a broken drive pin. Can I replace it with a roll pin?

I'd say yes

blsnelling said:

As mentioned above, the problem was a broken drive pin. Can I replace it with a roll pin?

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I'd also say that the O-ring is #4 and the washer is #2. anybody else in agreement here???

I figured it out. #4 is the washer. It goes against the spring and pushes the o-ring against the body of the pump.

blsnelling said:

As mentioned above, the problem was a broken drive pin. Can I replace it with a roll pin?

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Just order the right part - it's 40 cents.. part number 9371 651 1360. If you use another pin, it's a 2.5mmx11mm pin.

Wow! This has been service at it's best. We've also got to get a sprocket and a couple clutch shoes, so I'll see on getting the correct drive pin while I'm at it. Thanks again.

I'm with ciscoguy on the cleaning out of the pump every so often, but I like to use diesal fuel (straight) and let it run at high rpm's for a couple of minutes. It has a higher viscosity that kerosene.
Works for me..
Jus my .02 worth

I'm not sure why you guys are having so much trouble with cleaning out your oil tank... If you use a decent quality bar oil (not old engine oil, 90WT fluid, or whatever junk) the oil pumps and filters just don't block...

blsnelling said:

Wow! This has been service at it's best. We've also got to get a sprocket and a couple clutch shoes, so I'll see on getting the correct drive pin while I'm at it. Thanks again.

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If you need two clutch shoes, get three... then they are all the same size IF shoed. Later clutches on the 041 just has metal shoes and you might as well just upgrade. Replace the clutch springs while you are in there - a couple of $ each.

Lakeside53 said:

I'm not sure why you guys are having so much trouble with cleaning out your oil tank... If you use a decent quality bar oil (not old engine oil, 90WT fluid, or whatever junk) the oil pumps and filters just don't block...

Click to expand...

I second that...

Ight

Lakeside53 said:

I'm not sure why you guys are having so much trouble with cleaning out your oil tank... If you use a decent quality bar oil (not old engine oil, 90WT fluid, or whatever junk) the oil pumps and filters just don't block...

Click to expand...

Ok, this is why. I always use top quality oil for my bars/chains. Problem is, have you ever noticed all the woodchips around the filler cap when you open it? Some of them fall in. They usually rot etc... They cause buildup. There's nothing you can do about it. It happens to EVERYONE'S saw, there's no exceptions. Now if you only keep a saw for a few years, you prolly have nothing to worry about. I myself have only had a problem maybe one time that I can think of. My saws are pretty much all 70's saws, so they get alot of use still, even after over 30 yrs. Just one thing, you come to this neck of the country with your 90wt oil and you'd be finding out that you'd be changing chains twice a day. That stuff runs like molasses when it gets cold here bud. We have to run thinner oil, 90 is fine for summer, winter time we run thin thin oil. We have to guy... No offense guy, but it's just different everywhere. Don't take this as a negative tone, I just figgered I'd tell you exactly why/how it happens here.

I believe you misread my post - the 90 wt is "junk" and I throw it out of customer saws all the time.

Ohhhhhhh, lol

Lakeside53 said:

I believe you misread my post - the 90 wt is "junk" and I throw it out of customer saws all the time.

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I do know alot of people that use 90wt though. Sorry for the confusion eh? Looks like we're on the same page...

I have actually seen STP or Motor-Honey in a bar oil tank. This stuff won't flow at 80 degrees, much less 20 or 30. I asked the guy why he'd done it, he wanted to make sure that the oil was sticking to the bar. It sticks to everything, too bad it won't pump. Wound up costing him a new tank and some serious labor because at first he wanted me to clean the tank out although nothing will dissolve that crap. Later we put a new tank in it.