Piston Removal - why this advice please?

Discussion in 'Crazy-Awesome almost Dakar racers (950/990cc)' started by RedRupert, Jul 16, 2013.

  1. RedRupert

    RedRupert Brit in the Soviet Union

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    Please can someone explain to me why KTM say this in their Repair Manual:

    ----------------------------------------------------------------------------
    ! CAUTION !

    – DO NOT PULL THE PISTON OUT OF THE CYLINDER UP TO THE OIL SCRAPER RING
    SINCE THE PISTON RING WILL BE DAMAGED BY THE LOWER EDGE OF THE CYLINDER.


    ----------------------------------------------------------------------------

    I have never come across this with other motorcycles.​

    I can't see any way that the ring(s) can be damaged if the piston is removed from the bottom of the cylinder. There is a sharp taper at the very bottom of the cylinder, but that can only help, not hinder.​

    I can't see any damage to the rings after removing the piston downwards.​

    Thanks.​

    Rupert​
    #1
  2. StevenD

    StevenD Hmmmm, dirt!

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    I follow the manual on this but also have no clue. Mounting with the piston already in the bore makes it real easy though!
    #2
  3. RedRupert

    RedRupert Brit in the Soviet Union

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    It's true, but I needed to replace a valve-stem oil seal. The cylinders were off, so I'd rather remove the piston than disturb the expensive head gasket.
    #3
  4. CRW

    CRW I dont want a pickle

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    it can be done just be careful, there is a chance of damaging a ring. I have done it but installed new rings prior to assembly.
    #4
  5. RedRupert

    RedRupert Brit in the Soviet Union

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    What should one be careful of exactly - I mean compared with any other engine?
    #5
  6. charlie264

    charlie264 Long timer

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    :dunno Just leave the pistons in the bores if you can get to the gudgeon pin ....pop um out from top.
    #6
  7. StevenD

    StevenD Hmmmm, dirt!

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    I understand you want to leave the head gasket alone. My valvespringcompressortool won't reach with the cyllinder attached though, I think its gonna be much easyer to just spend the dough..
    #7
  8. RedRupert

    RedRupert Brit in the Soviet Union

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    I have already done the work - I used a large plug in the cylinder to hold the valves shut while I used a standard valve-spring compressor (against the plug and the valve springs). It was easy and well worth doing in order to save having to spend €80 on head gaskets.

    My question was: why should the piston not be removed from the bottom of the cylinder. I can't understand how the rings can be damaged by doing so.

    Sometimes the English version of the Repair Manual is poor. Do you speak/read German - if so, does it read the same in German?

    Thanks, Rupert
    #8
  9. CRW

    CRW I dont want a pickle

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    I think there is a possibility of snagging a ring upon removal. With two sets of hands assembly is easy. If you are carful should be fine. I did this when I swamped cases due to cracked cases. Then blew a head gasket 4000 miles later. Might be worth cracking the heads just for peace of mind.....
    #9
  10. mbrick

    mbrick Been here awhile

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    Funny you brought this up. I was also puzzled by the 690 manual talking about only sliding it down enough to remove the wrist pin, then taking it out the top of the bore.

    Is it possible the ring can be damaged because it doesn't jump out of the cylinder on the entire circumference all at once? (There are the 2 areas that extend further down into the lower case on the front and back). Really reaching here though.
    #10
  11. Zuber

    Zuber Zoob

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    You might scratch the face of the rings on the bottom of the cylinder. KTM removes and installs the piston from the top.

    Much easier to keep it in the cylinder and pull the piston pin.

    Good luck on putting the pin keeper back in, they are really stiff. There is a special tool that makes this a breeze. Without it I've had the best luck using a small screw driver to pry it back in.
    #11
  12. mbrick

    mbrick Been here awhile

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    Mocking it up I actually noticed how stiff it was and how tough it will be.

    Do you happen to have a photo of the tool? I can't quite see the end of it in the photo in the service manual to see how it works.

    Thought about making a bore and inserting it inside the bore, then "knocking" it through into the opening on the side of the piston.
    #12
  13. RedRupert

    RedRupert Brit in the Soviet Union

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    You say 'back in' do you re-use them?


    I've installed LC8 piston circlips (pin keepers) several times. There is no need for a special tool, as it's a breeze when you know how. This is how it's done:

    1) Locate the tail of the clip into the notch in the piston: 'A' below.
    2) Support the clip with your left thumb - applying a little pressure towards the centre and towards the piston pin - at point 'B'.
    3) Use a stick or rod to gently push the circlip towards the piston pin, starting just to the right of point '1' and working CCW, do the same at points '2' and '3'. Take it easy - it's similar to fitting a tyre - the last bit just slips in and snaps into place.

    [​IMG]

    I use a hardwood dowel, about 8mm in diameter and 100mm in length - there is no danger of fragments splintering off and getting into the engine. Perhaps better would be a soft aluminium, bronze, brass or copper rod - whatever you use, it needs a square-cut end i.e. not rounded so that it slips. A screwdriver is too aggressive, and may damage the clip seat or leave marks on the piston if it slips.

    I recommend you practice using an old/used circlip - then install a new clip when you've sussed it.
    #13
  14. dmn0507

    dmn0507 Been here awhile

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    If You are going to follow the manual (install from top) you need a ring compressor, otherwise a piece of plastic is enopugh to work your way in little by little.
    #14
  15. RedRupert

    RedRupert Brit in the Soviet Union

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    Thanks, but a ring compressor is not needed whether inserting the piston in from the top or bottom - it's quite easy and safe to insert a single piston into a single cylinder, specially when on the bench. I know KTM recommend it, but it's not imperative.

    It's one of the reasons I asked the question in post #1 of this thread - why can't one remove the piston from the bottom of the cylinder - is it imperative or just good practise or recommended.
    #15
  16. mbrick

    mbrick Been here awhile

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    Redrupert thanks for the suggestions on inserting the clip. I was going to try something along those lines. I did order a new one for the side I removed.

    I agree, will probably insert the piston into the jug on the bench without a ring compressor, and have a friend help hold the jug while putting in the circlip.
    #16
  17. Peanuts

    Peanuts Long timer

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    If you lay the engine on its side, with the cylinder and crankcase supported, its easy to offer up the rod to the piston and push in the pin/fit the clip.
    #17
  18. charlie264

    charlie264 Long timer

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    I just use needle nose pliers and twist the clip in....Am I bad...never had one come out...
    #18
  19. RedRupert

    RedRupert Brit in the Soviet Union

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    Peanuts said: If you lay the engine on its side, with the cylinder and crankcase supported, its easy to offer up the rod to the piston and push in the pin/fit the clip.

    Charlie264 said: I just use needle nose pliers and twist the clip in....Am I bad...never had one come out...


    You two guys generally provide good experience-based information, therefore please can you answer the question that I raised in this tread - look at post #1 to know it?

    Thanks
    #19
  20. rider911

    rider911 Shortcut Navigator

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    I see you are having trouble getting inmates to answer your ACTUAL question:hmmmmm

    Its abit like emailing a part supplier and asking 3 or more questions.... more chance of winning lotto than getting 3 answers :lol3

    My opinion is that there can be no possible downside to installing the piston from the bottom if you take appropriate care.
    I have noticed that there are other strange assembly procedures in the workshop manual that are either bad translation or KTM techs taking the piss out of us. One of them is the assembly of the clutch.


    .
    #20