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  1. #1
    Join Date
    Apr 2018
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    Default How to polish recessed O-ring seats in cast iron?

    My old Ford 4100 tractor has a diverter valve on the top cover for loader hydraulics, the hydraulic power for the 3-point linkage passes through the interface between the valve and the top cover. When I have a heavy-ish implement on the 3-point linkage, hydraulic oil leaks out from between the valve and the cover. All the O-rings were renewed about a year ago when I did a heap of work on the tractor, fixed all the other oil leaks but this one persists. The two mounting surfaces were a long way from flat, so I've used the surface grinder to make them flatter than a dunnyman's hat, now I need to clean up the surfaces in the bottom of the O-ring recesses to give the new O-rings a fair chance of sealing.
    diverter valve surface with bad seats.jpg

    There are 9 recesses in 6 different sizes. The valve body is cast iron. My plan is to turn a piece of stock to match each recess diameter, mount the valve in the mill and use some lapping paste on the face / end of the round tools to polish the bottom of each recess with light pressure on the quill. My main question is am I best using steel, aluminium, hardwood, softwood or something else for the polishing tool? A second question would be any other suggestion to make sure these O-rings don't leak again.
    And yes the mounting lugs are broken but I have already sorted a method of clamping it down tight so that is not a worry.

  2. #2
    Join Date
    Sep 2006
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    Mallacoota,VIC,Australia
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    Default

    I agree with the lapping compound ( fine valve grinding/lapping paste). Another one would be Jewellers Rouge, I never usd it myself though so I don' know what it would be like - might be too fine. XEBEC® Deburring Technologies The weblink has deburring stuff, but they might be over the top. Someone else might have some other ideas.
    All The Best steran50 Stewart

    The shortest way to do many things is to do only one thing at once.

  3. #3
    Join Date
    Apr 2012
    Location
    Healesville
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    2,129

    Default

    G/day Pete, I would normally just use a wire brush in a drill, maybe get into the corners with a blade screwdriver or the end of a knife, sometimes have used emery tape if it can be used in a circular motion.

    The surface on the small hole right in the middle looks like it has a dent and the large hole just above it to the left also looks like the seat face has damage.

    They might need more than a polish.

    You might also want to check the depth of the oil ring seats and the thickness of the o rings, just at a guess with that type of o ring use I think that the o ring should be about 1/3 thicker than the depth of the hole, but you would need to check that.

    cheers, shed

  4. #4
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    Apr 2018
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    Default

    Yes I expect some of the recesses will need to be bored a little deeper as there was a fair bit of concavity in the surface so it was ground down by several thou. I may even bore one of them a little bigger in the diameter as it was an odd size and the O-ring selection was either too small or too big. I'll look for a chart that specifies compression % for O-rings, probably got one somewhere.
    Barring other suggestions for lapping, I think I'll try a dremel polishing pad with lapping compound for starters. Perhaps work down to a finer polishing compound. Won't get back to this now for several days.

  5. #5
    Join Date
    May 2011
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    Murray Bridge S Aust.
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    Default

    Found this on our friend Mr Google. Makes for some interesting reading.
    http://blog.parker.com/selecting-the-right-o-ring-seal-squeeze-ratio#targetText=When%20compression%20set%2


    Kryn
    To grow old is mandatory, growing up is optional.

  6. #6
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    Apr 2012
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    Healesville
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    Default

    I don't think that is a good idea to polish the surface for a static o ring surface, that is why i suggested using emery in a circular motion, following the direction of the o ring circumferance and not in the direction of the diameter
    I just did a quick search on this before i opened my mouth again to confirm surface roughness/finish, so you should find info about that.

    cheers, shed

  7. #7
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    Apr 2018
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    Default

    I managed to get back to this job yesterday. Did a bit of research (and thankyou to those who linked tech articles) and it seems an ideal O-ring squeeze for most purposes is 30%, so I re-seated the face of the valve. Had to borrow a boring head from a mate as I have not yet got much in the way of R8 tooling. I ground a 'D' bit in HSS and re-cut each of the O-ring seats, including enlarging the diameter on a couple of them to suit O-rings I had in my kit.
    diverter valve O-ring seat boring.jpg

    I made a simple tool from a slug of aluminium bar stock; turned one end to 20mm, put my ER32 collet chuck in the lathe and then turned the other end of the al bar to the diameter of the largest O-ring seat. Put the tool in the mill collet, applied some valve lapping paste to the seat and gave it a touch up. Tool back to the lathe and turned down to the next-largest O-ring size, back to the mill and lap the next seat, back and forth from the lathe to the mill until the smallest seats were lapped. Thank goodness for collets.
    O-ring seat lapping tool.jpg

    Got a reasonable surface finish in the seats, the scratches are at least circular so shouldn't provide a leak pathway.
    diverter valve O-ring seats done.jpg

    Managed to get the tractor back together last night. I won't know how successful this has been until I get the chance to put a heavy implement on it. I had to put a flat top surface on the valve casting to hold it in the mill, tried flycutting it with HSS and the tool bit wore away faster than the workpiece, so I used the surface grinder instead. Going to have to paint it again now.
    diverter valve with top ground.jpg

  8. #8
    Join Date
    Aug 2015
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    QLD
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    Default

    I think the Ford 4100 is pommy made. You do know that British machinery is supposed to leak oil.










    ..

  9. #9
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    Sep 2012
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    Default

    Quote Originally Posted by YBAF View Post
    I think the Ford 4100 is pommy made. You do know that British machinery is supposed to leak oil.
    ..
    You realise that is just a malicious rumour
    Best Regards:
    Baron J.

  10. #10
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    QLD
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    Quote Originally Posted by BaronJ View Post
    You realise that is just a malicious rumour
    Heh... I were told that by my father who did his mechanic time on mainly British cars back in the 40s..




    .

  11. #11
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    Apr 2018
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    Drouin Vic
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    Default

    Your father may have been right YBAF. Fixing a leak up high just reveals all the leaks lower down.
    I put the slasher on and gave it a bit of work this morning, the repair seems to have been successful but there are 2 more leaks to fix


    There's an O-ring on this plug under the diverter valve
    leaking top cover valve cap.jpg


    and there's a copper washer behind this plug on the thingamajig valve.
    leaking valve plug.jpg

    At least these two are accessible.

  12. #12
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    Apr 2018
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    Drouin Vic
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    Default

    A new O-ring, a few drops of 542 and no more leaks! Happy days.

  13. #13
    Join Date
    Oct 2010
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    melbourne, laverton
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    1,910

    Default Maybe

    Just thinking would something like valve/tap miter gear be suitable?.
    Maybe there called tap rosette.
    Like this
    https://fixatap.com.au/fix-a-tap/tools/tap-reseaters
    Azz

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