Modifying the Stihl 084 oil pump for increased flow

[markds2]

I have been very hesitant to post this, but as it is the second 084 I've found with exactly the same fault I felt it my duty (and I was encouraged to by another member) to post about it, as it may help others solve the same issue - as it stands to reason that if I've found it on two 084's there may be more out there like it!

Background to the story is that I was sent this early 084 (it has the early unlimited coil with the separate trigger) over a year ago, with the owner complaining that the oil pump was, and had always been, very anemic with between a 1/4 and 1/3 of a tank of oil being used for every tank of fuel. He did mention that it poured oil out when he held in the auxiliary button (but who wants to do that all the time), but with the pump adjusted to maximum it had very poor flow, and could hardly oil a 30-inch bar. I got the saw and carefully inspected the pump, and it looked to be in perfect condition internally, I did all the seals and O-rings and replaced the hard black tube that routes the oil from the pump to the bar pad (someone had used tygon fuel hose!). I tested the saw, and it seemed to oil OK when just eyeballing the flow from the bar pad, so I sent it back to him.

He soon complained that oil flow was no better, and in the meantime, I found that my own ported o84 (which is considerably newer - going by serial numbers) exhibited the exact same symptoms, the pump would work, but the flow was useless. So back in September I dismantled the pump and found the following fault, which has to be from the factory. The pictures below are from the first 084 (which my customer sent back to me), which exhibits the exact same manufacturing fault as mine:

To understand properly, first I need to explain how the pump works. The following picture shows the pump piston, which, as it is spun, moves in and out, through the action of the 'ramp' on the RH end.

You can see the ramp through the hole where the control bolt is meant to reside:

And again here, looking at the end of the pump, with the control bolt in place:

 

[markds2]

Now on close inspection, I found that there was a clear witness mark on the control bolt, showing where the 'ramp' had been running for a very long time (given that the owner said he always adjusted the pump to maximum). When I saw this witness mark, a lightbulb went on somewhere:

Because this witness mark is not on the 'cam' of the control bolt, which would increase the travel of the pump piston:

 

[markds2]

Now the position of the adjustment cam, in relation to the 'ramp' on the pump piston, is determined by this little stepped pin:

Which sits in this little stepped hole at the end of the control bolt:

The range of motion is controlled by this 90-degree slot cast into the pump body:

 

[markds2]

In looking closely I determined that the little stepped hole in the end of the control bolt had been drilled 90 degrees out, meaning that the adjustment cam on the control bolt, would never engage with the 'ramp' on the pump piston - essentially the pump was always adjusted to a minimum, no matter where you turned the control bolt:

This theory also fits with the symptoms - the pump would pump, but only poorly. The solution? Grind the pump body, to give an extra 90 degrees of motion to the control bolt:

And back together, you can see the control bolt now through the bottom of the saw with an extra 1/4 turn available:

 

[markds2]

And the two saws, that had exactly the same fault:

 

[markds2]

Now my question, for science and stuffs, is, has anyone else come across this problem? And, if anyone has an 084 that oils well, would they be prepared to pull the pump off to prove my theory? (You wouldn't need to remove the control bolt, just look down the end of the pump)

 

[Mastermind]

Excellent thread !!!!!!!

This sort of stuff is what keeps a saw forum alive.

Thank you Mark.

 

[Kiwioilboiler]

Good stuff bro. I get it now.

 

[huskyboy]

My 064 I had to grind a tad bit too on the pump stop to allow a tad more adjustment out like you did. It oiled poorly before. Oils good now. The oiler is a little different than the 084’s. But a similar problem existed where the offset on the end of the bolt was not actually at maximum position when the adjustment screw was turned to “max”. The ramp, offset and adjustment screw position all have to match at max position or you won’t get good results. One can limit the other.

 

[jacob j.]

So this begs the question of whether the control bolt was made by Stihl in their factory, or sourced from a third party? This is a lot like how the oil scraper rings in some of the
early 2000's Volkswagen engines were installed upside down, causing those engines to consume considerable quantities of oil. The reason the rings were installed upside was
that the directional arrow on them was laser-etched the wrong way at the piston ring manufacturer.

 

[huskyboy]

Are the oiler parts cast or machined? If some of them are cast then that allows for variation I would imagine.

 

[markds2]

Are the oiler parts cast or machined? If some of them are cast then that allows for variation I would imagine.

The pump body is definitely die-cast. The internal components I would imagine are machined - they're extremely hard!

 

[rogue60]

Who's to say it's even a fault? for some reason Stihl seem to have gone down the road of less is more when it comes to oiling the bar and chain on a lot of there pro saws over the years.
Like what's up now day's with nocking in the stupid pin just to gain an extra ml or two lol

 

[markds2]

So, guys, I have a confession to make. After extensive further research, testing and trial and error, I have to say all the assumptions and modifications I made about and to the 084 oilers above were wrong!

Now before you all kindly lynch me, I want to explain and also offer a modification that actually does work!

 

[markds2]

So, on my own 084, after making the modification above, I found that the oiling was no better and in fact actually sightly WORSE than before!

That really got me thinking and before long I had the opportunity to purchase a good secondhand oiler, which apparently came from Canada (cost me $185NZD, but that is beside the point). On inspection of this oiler, I found it set up EXACTLY the same as the two mentioned earlier in this thread, with the control bolt seemingly set up 90 degrees out. That really got me thinking.

Now, if we study the exploded parts list, we see that the 084 oiler is quite different from any other Stihl oiler we have seen, given that we can increase the flow dramatically by pushing a button to the left of the rear handle, which pulls a cable, which in turn pulls back on a part called a 'control slide' (part 16 below).

Now given that spring #17 is much bigger and stronger than spring #8 above (which enables the oil pump plunger to operate backwards and forwards on the ramp as it is spun), and the fact that the 'fork' on the control slide contacts the pump plunger (#2 above) I deduced that it was actually this 'control slide' that dictates the length of the stroke of the pump (and therefore the amount of the oil pumped) rather than the relationship between the control bolt (#10 above) and the pump plunger.

 

[markds2]

And, if you think about it, this makes sense. The control bolt (in its factory configuration - without my modification) controls the position of the control slide, and with the pump turned to maximum, pushes it further away from the pump plunger (as does pushing the oiler button beside the back handle) allowing a longer 'stroke'.

Here you can see the control bolt, with the pump turned to maximum, with the eccentric on the bolt curving away to the left (circled below):

Here I am inserting the control slide, it is forked so it straddles the control bolt, the ends of the fork contact the pump plunger, and the ridge halfway along is what rides up against the control bolt

 

[markds2]

Now the explanation is over, what did I do to modify the pump, so we solved the issue of a lack of oil flow?

I ground .8mm off the 'fork' end of the 'control slide', carefully ensuring it was dead flat and the edges were chamfered (like it came from factory). It was extremely hard, so I don't think machining was an option.

here is the 'control slide' as factory:


And with .8mm carefully ground off the end of the 'fork', and the edges chamfered:


Note, that to make sure this modification works, ensure the pump is set to the factory maximum position and there is no need to modify the body of the pump as I thought earlier, and explained when I first made this thread.

 

[markds2]

And yesterday, I finally got a chance to try the saw with a 42 inch bar, full comp chain, fully buried in hard dry old Eucalyptus. And I'm pleased to say it performed really well. 70 to 80% of the oil tank was used to the one tank of fuel I burnt and the chain was adequately oiled, and it easily flung oil off the tip of the bar when I piss revved it. I also made the same modification to my friends' 084 (one of the two shown on the bench earlier in the thread) and he reports exactly the same results.

 

[markds2]

If my explanation doesn't make sense or is too complicated, please tell me and I'll try and clarify!!

 

[zero_sum]

Excellent follow up!

I've never paid attention to my 084 oil output.... but now I will have to.