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How to spot a bad oil pump, need advice (Stihl ms260 Adjustable vers)

Discussion in 'Chainsaw' started by MartDalb, Feb 14, 2020.

  1. MartDalb

    MartDalb ArboristSite Operative

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    Hi folks

    I need some advice on oil pumps :)

    One of my Stihl MS260 needs a new oil pump, and I found a used one in some old parts etc.

    But, after having it cleaned and oiled up etc, the pump "drive wheel" (See picture) runs smooth, but sometimes needs more "pressure" to spin around.
    It is not entirely "free spin", as I my old, but apperently, broken non adjustable oil pump was.


    My question here, will this ruin the plastic worm gear? or do they all act like this?

    Any help is appriciated! :)


    oil pump.jpg
     
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  2. Brent Nowell

    Brent Nowell Addicted to ArboristSite

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    The oil pump is a type of reciprocating pump. From what I remember taking apart the one from my 550 the shaft itself strokes up and down. The position of the adjustable screw determines the throw of the shaft per 360 degrees of rotation, and in turn how much oil is displaced.
    Really quite clever design.
    Point being what you are experiencing is the pump working, trying to displace fluid upstream and downstream of the pump body.
    There will be some resistance when this happens. If you can overcome it if your finger a hardened nylon reinforced plastic worm gear will have no problem.

    I test the pump by installing it and and spinning the clutch drum manually until I see oil.
    There must be no tears or leaks in the hose upstream of the pump to the tank or it will not pump properly. Especially so on thicker oils. The pump displacement is so small that a leak in the hose will allow atmospheric pressure to bleed in, eliminating the vacuum that it is supposed to make and thus it will not pump.
     
  3. MartDalb

    MartDalb ArboristSite Operative

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    Thanks for the reply!

    I did install the pump, but I have no working/intact wormgear on hand for the "adjustable pump" like this, so I had to turn it manually.
    It did indeed pump oil out, once turned enough and having air pressure into the oil vent for vacuum.

    My next step will then be buying a new worm gear, wondering if I need to stick to "Stihl original" or aftermarket, i'm reading many mixed answers on especially oil pumps/wormgear etc. :eek:

    A new genuine pump is crazy expensive, hence my question about the pump issue. (I am Euro so prices are not the same as US)
     
  4. Brent Nowell

    Brent Nowell Addicted to ArboristSite

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    I personally find this particular style to be really robust and not likely to fail. Considering the worm gear is the weaker link in the mechanism this is probably designed to fail before the pump, say a piece of hard sediment went down the line and made a lot of resistance. I don’t have the experience to say this for certain as there are others on this board who fix for a living. I suspect they will probably agree
     
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  5. MartDalb

    MartDalb ArboristSite Operative

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    Yeah, I see your point.
    My other 260 runs with the old pump, haven't failed since 2004.

    oddly enough, the one that broke down is from 2011, used more or less the same amount.

    Prices here are weird, the old version oil pump is even more expensive than the new one, I have everything on hand for the new pump, cept for that worm gear.

    Guess it's time to buy a new wormgear and test it :)
     
  6. Brent Nowell

    Brent Nowell Addicted to ArboristSite

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    So how is it broken? Given all things said here maybe it isn’t?

    if your not sure why it stopped working maybe investigate it further to see why.
     
  7. MartDalb

    MartDalb ArboristSite Operative

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    No, sorry if I didnt explain it well enough.

    The "old non adjustable" oil pump failed on me, and I know this for sure, tested it, and no oil flows through it at all, no idea why. It doesnt pump any oil out etc, tested it and it's just broken.

    But I had a used "adjustable" oil pump, which led me to my initial question.

    I won't be getting a new oil pump, seeing as you replied it should work as intended, just a new worm gear :)

    Thanks for the help again! :)
     
  8. Conquistador3

    Conquistador3 Le Comte de Frou Frou

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    I've stopped bothering with aftermarket oil pumps, worm gears etc three or four years ago. Plainly put you get what you pay for.

    If I remember correctly the oil pump on the MS240/260 was changed at some point during the production run with a new design: after a while there was a technical bulletin from Stihl strongly advising against mixing worm gears and pumps.
    If you are fitting the pump in the first picture be sure to get the old style worm gear, part #11216407110.
     
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  9. drf255

    drf255 BAD CAD

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    There is a sleeve and washer you will also need to make the adjustable work, not just the worm gear. And then you’ll need a clutch drum.

    The 026/260 adjustable worm gear has a straight drive tang, unlike all the other Stihl models which have an S bend at the end, this makes it easy to ID.

    It’s an expensive “upgrade” that really isn’t necessary. The washer goes on the crank first, which locates the sleeve that the worm gear slips over. The worm gear drive on the adjustable is clutch drum driven, and the standard drum isn’t deep enough to engage it.

    So the kit includes the pump, worm, drum, sleeve and washer.

    Find a standard pump and bolt it on. Your best bet.
     
  10. MartDalb

    MartDalb ArboristSite Operative

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    Solid advice! I will make sure to get a Stihl version, not an aftermarket. :)
     
  11. MartDalb

    MartDalb ArboristSite Operative

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    Yeah thanks for the tips, much appriciated! :)

    Luckily I have all that around, just not a working worm gear.

    If I had an old ill actually prefer that too, I just dont have one and they are even more expensive than the "new version" oddly enough? :dumb:
     
  12. Brent Nowell

    Brent Nowell Addicted to ArboristSite

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    I’ve made a worm gear out of a soda bottle cap once, I’ll tell you how.


















    Just f*in with ya, ur gonna have to buy one! ;)
     
  13. MartDalb

    MartDalb ArboristSite Operative

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