Stihl Oil Pump Flow Mods

[Maintenance Chief]

Low side of the oiler shaft after modifications, I was pretty nervous about screwing this up so I basically wrapped some 800 grit sand paper around a block of tool steel and sanded it by hand, I doubt I took more than .005 off it.

 

[Maintenance Chief]

Reassembled and used my small hammer to seat the bronze bushing back in flush.
Original pump out and installed the new one.

 

[Maintenance Chief]

It is dark outside so I didn't mount the bar to it ,but i couldn't have messed it up too bad because the " modified pump does pump oil.
I seems to be a more steady stream of oiler rather than a pulse of oil , so I'm hopeful that it will oil a 28" with out effort.
One thing I should have done was pull the oil feed line out of the tank while I had the oiler out considering the saw came out of a junk yard. Well anyway I'll give it a try tomorrow and see how I did.

 

[qurotro]

I hope it don't over oil your bar..
I've found out those ramp and bolt are pretty sensitive. A little bit of grinding makes huge difference. My Asian 660 is thirsty for both chain oil and gas

 

[drf256]

Making the oil slot larger in the tail of the piston is a waste of time IMHO.

Think about it. What pumps out is the change in volume between piston up and piston down. All opening the slot does is increase both volumes but doesn’t change the difference in volume. That remains constant.

 

[Maintenance Chief]

Making the oil slot in the tail of the piston is a waste of time IMHO.

Think about it. What pumps out is the change in volume between piston up and piston down. All opening the slot does is increase both volumes but doesn’t change the difference in volume. That remains constant.

Making longer? Or deeper ? ( not being dirty) or both have no effect on volume of out put?

 

[Maintenance Chief]

Happy to report that the ms441 will oil the 25' wet and adequately oil a 28" bar now. I think if I had proper tools and wasn't as conservative it would oil a 32-34 inch bar.
Thank you OPs for starting this thread I appreciate it.

 

[drf256]

Making longer? Or deeper ? ( not being dirty) or both have no effect on volume of out put?

I believe changing the size of it does nothing, I could be wrong. It’s all in the ramp and altering the control cam so that the movement of the increased ramp can actually happen.

Increasing the size of the slot will increase the volume in the cylinder of the oil pump before and after it rises and falls a constant amount.

So let’s saw the pump will be 1cc full with piston up and .5cc full with piston down after a pump cycle. .5cc will be pumped out per revolution. You make slot deeper or longer (wider might cause worse oiling as it affects open and close vs stroke timing) and now you are at 1.2cc full and .7cc empty. You still only pumped .5cc out in one stroke.

I could be seeing it wrong, but I haven’t noticed any difference or seen any need to modify the notch.

 

[Maintenance Chief]

I believe changing the size of it does nothing, I could be wrong. It’s all in the ramp and altering the control cam so that the movement of the increased ramp can actually happen.

Increasing the size of the slot will increase the volume in the cylinder of the oil pump before and after it rises and falls a constant amount.

So let’s saw the pump will be 1cc full with piston up and .5cc full with piston down after a pump cycle. .5cc will be pumped out per revolution. You make slot deeper or longer (wider might cause worse oiling as it affects open and close vs stroke timing) and now you are at 1.2cc full and .7cc empty. You still only pumped .5cc out in one stroke.

I could be seeing it wrong, but I haven’t noticed any difference or seen any need to modify the notch.

I see what your saying , its a contstant in the pockect regardless of the other factors.

 

[drf256]

Yes. Exactly. And the width is timed to the ramp, so widening it may just cause short circuiting back out the feed.

 

[Maintenance Chief]

So the oiler is working well, thanks again.

 

[Terry Syd]

What pumps out is the change in volume between piston up and piston down.

The pump is a positive displacement pump, but it can only displace the oil that is IN the pump. OK, if the pump can suck in 1cc of oil, BUT because of the oil viscosity or a weak spring to push the piston all the way back it will only suck in .8cc - then that is the output of the pump.

If after the mods you may not be getting the output you think you should be getting. Perhaps put a few washers under the return spring to increase the pre-load and make sure you are getting full travel.

As far as opening the hole on the bar, the better idea is to put an angle (perhaps 45 degrees) on the inside of the hole facing the direction of the oil flow. Most of the problems with a hole in the bar is the sawdust begins to clog the hole. An angled hole will keep the sawdust and oil flowing in the right direction.

 

[sawmikaze]

I just put one of these bolts in a 261 Kevin ported. Easy Peasy...and worth the 6 bucks it cost me.

 

[brianc636]

Just got a brand new 22’ MS261CM version 3.0 saw with the 18” bar. Does the bolt and maybe piston swap still work on the new saws?

Thanks,

Brian

 

[sawmikaze]

Just got a brand new 22’ MS261CM version 3.0 saw with the 18” bar. Does the bolt and maybe piston swap still work on the new saws?

Thanks,

Brian

Yes.

You don't need the piston, it oils way better with just the bolt.

 

[brianc636]

Yes.

You don't need the piston, it oils way better with just the bolt.

Thank you Sir!

 

[brianc636]

Ordered the bolt from my local dealer for 2.50. Can’t beat that with a big stick!