MS 291 leaking bar oil. But not from the usual place. Help!

[malquid]

Scratching my head on this one. I’m having a hard time figuring out what is going on with my Stihl ms291. It’s leaking bar oil from the oil outlet when it’s off. It’s not residual. I cleaned everything up and it If I lay it on that side it drips out of the oil outlet.
All I can think of is that the pump must have a check valve that’s not working and to throw parts at it with a new oiler and pump.
Thanks guys.
First post. Blast me if I got it in the wrong spot or this is already covered somewhere.

 

[SteveSr]

Check valve is that round thing in front of the front bar stud. It is working fine as it lets air in but stops oil from going out.

It also allows the tank to pressurize slightly from changes in temperature between day and night. This may push some oil through the pump and out the outlet. If this leak is excessive it means that the pump likely has sawdust lodged in it. You can either replace the pump or attempt disassembly to clean out the crud.

 

[malquid]

Check valve is that round thing in front of the front bar stud. It is working fine as it lets air in but stops oil from going out.

It also allows the tank to pressurize slightly from changes in temperature between day and night. This may push some oil through the pump and out the outlet. If this leak is excessive it means that the pump likely has sawdust lodged in it. You can either replace the pump or attempt disassembly to clean out the crud.

I really appreciate your reply Steve. I was ready to buy a new pump but thought I’d ask someone who’s seen this. There’s a wealth of knowledge here. I’ll see if I can can clean out the pump. Looks like they are going for around 50 bucks.
I’ve been known to whittle a part from a recycled Barbie doll with a butter knife to save 90 cents

 

[HarleyT]

It is just a little style stick pump like in a ms170 or ms250 just stuck in a plastic body, so I am not sure how it could pass through while the saw is not running.

 

[SteveSr]

It is just a little style stick pump like in a ms170 or ms250 just stuck in a plastic body,

That is what I suspected.

so I am not sure how it could pass through while the saw is not running.

The crud restricts pump piston movement which prevents the piston from completely closing the oil port. Usually you will also see reduced oil delivery (due to limited piston travel) when the saw is running.

 

[HarleyT]

It would be interesting to crack one apart and see the shape of the impeller, see exactly how it's action works.

 

[SteveSr]

It is easier to see on an older pump like the metal adjustable ones on an 026/MS260 that you can disassemble by pushing out a roll pin. The piston goes up and down on a cam while the rotation opens and closes the intake and output ports at the appropriate time. I am assuming that the "stick" ones operate on the same principle. A quite clever design.

This is why they must be disassembled to be cleaned. There is no straight path through the pump other than minimal leakage around the piston.

 

[ValleyForge]

Just curious, how much oil? Are you draining the tank?

 

[ValleyForge]

It would be interesting to crack one apart and see the shape of the impeller, see exactly how it's action works.
View attachment 1008594

I believe it’s juat a rotary lobe type pump.

 

[malquid]

Just curious, how much oil? Are you draining the tank?

If it sits long enough over a few months it will drain the tank. Normally my saw doesn’t rest for a whole month but the back of my truck looks a jiffy lube pit.

 

[malquid]

I believe it’s juat a rotary lobe type pump.

Valley, I am sure you are right.
The ms291 does not have the metal barrel pump. It has the plastic rotary one that Harley posted above.

 

[malquid]

It is just a little style stick pump like in a ms170 or ms250 just stuck in a plastic body, so I am not sure how it could pass through while the saw is not running.
View attachment 1008538View attachment 1008539

You are correct, it is one of these.
In your honor, I will disassemble it next week when I get the parts and send pics of what I find.

So far, no one on you tube has addressed this. It’s always the cap, the rubber hose or the vent sticking open.
Cap 90% of the time. But captain obvious knew that

 

[HarleyT]

Well let me know if you are buying a new pump, I can cut you a good deal.

 

[HarleyT]

But make sure the oil line is in good shape.

 

[SteveSr]

You are correct, it is one of these.
In your honor, I will disassemble it next week when I get the parts and send pics of what I find.

So far, no one on you tube has addressed this. It’s always the cap, the rubber hose or the vent sticking open.
Cap 90% of the time. But captain obvious knew that

If you do replace the pump dump the oil tank into a clean glass jar to see how much crud is in the oil. Also flush the oil tank with mix to clean out any remaining crud.

If you found much crud in the oil or the tank you need to investigate your oil filling habits. It also wouldn't hurt to get a small flux or chip brush to clean the cap area before you remove the cap. Flippy caps are known for collecting crud that will eventually make its way into the tank(s).

 

[malquid]

If you do replace the pump dump the oil tank into a clean glass jar to see how much crud is in the oil. Also flush the oil tank with mix to clean out any remaining crud.

If you found much crud in the oil or the tank you need to investigate your oil filling habits. It also wouldn't hurt to get a small flux or chip brush to clean the cap area before you remove the cap. Flippy caps are known for collecting crud that will eventually make its way into the tank(s).

Great point, I’ve been guilty of this in the woods.
I always thought the pick up tube would filter anything out. Looks like I’m learning a lesson.

 

[HarleyT]

Great point, I’ve been guilty of this in the woods.
I always thought the pick up tube would filter anything out. Looks like I’m learning a lesson.

It ain't much.

 

[SteveSr]

It ain't much.
View attachment 1008735

If it filtered well then you couldn't get any oil through it. It only filters out the big chunks.

Stihl is hoping that anything small enough to get through the "screen" will go all the way through the pump. Sometimes it does and sometimes it gets stuck in the pump.

 

[malquid]

It ain't much.
View attachment 1008735

Well,, that answers that. It’s no mystery what happened now. That’s not a filter, it’s a grate at best.
Thanks guys. you are awesome. Harley, I would have got the parts from you but I ordered them yesterday.

 

[HarleyT]

Well,, that answers that. It’s no mystery what happened now. That’s not a filter, it’s a grate at best.
Thanks guys. you are awesome. Harley, I would have got the parts from you but I ordered them yesterday.

I hate to think how much you are going to pay for one.