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MS 170 Tear-down

Discussion in 'Chainsaw' started by roostersgt, Jun 18, 2011.

  1. roostersgt

    roostersgt Guest

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    Okay, I got a Stihl MS170 from a guy on Craigslist today for a 30 pk of Miller (MGD). The guy told me his neighbor used gas only in it and it won't start anymore. Checked fuel resevoir and yup, smelled like regular old gas to me. Checked bar oil resevoir and it looked and smelled like ATF.

    i got this beauty home, pulled the muffler and found much verticle scoring on piston. Pulled carb and that side of piston looked shiny. Well into tear-down as I write this and am looking forward to seeing the cylinder walls sometime tonight. Got most of it apart and was hoping I didn't have to pull the flywheel or clutch just to release the cylinder. Guessed wrong? Are both flywheel and clutch "reverse" threaded? The rope trick isn't working out well for me. Seems both are on exceptionally tight. Any suggestions would be greatly appreciated. Pics to follow later. Too freaking greasy to handle camera. Keyboards now a mess. Thanks.

    Steve
     
  2. bobt

    bobt Addicted to ArboristSite

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    Subscribing. I await your progress! I hope the cylinder is still ok.

    Bob
     
  3. K5krawler

    K5krawler ArboristSite Operative

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    I hope the cylinder is okay as well. Are you going to use Stihl repair parts or aftermarket? When I rebuilt my straight gassed 025 I had good luck with Northwood Saw and their quick shipping.

    -K5
     
  4. Rookie1

    Rookie1 Addicted to ArboristSite

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    Ask Snelling about tight clutches and the rope trick.:msp_w00t:
     
  5. bobt

    bobt Addicted to ArboristSite

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    Oh Yes! Snelling had a thread about him bending the stamped connecting rod on a 180 I think. He either used the rope trick or a piston stop. Evidently these rods are quite weak.

    It just might be better to use an impact wrench on these saws. Leave the spark plug in and use the impact against the compression (if there is any). The flywheel should be tackled first. It is right hand thread. Get the nut off and remove the flywheel. If you don't remove the flywheel first, you stand the chance of shearing off the key. Then go after the clutch. It will be left hand thread.

    Bob
     
    Last edited: Jun 18, 2011
  6. K5krawler

    K5krawler ArboristSite Operative

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    BobT...let me ask you. Why do people stray away from using impacts on clutches? If you just blip the trigger they come off, or at least the 3 or 4 I have taken off.
     
  7. Rookie1

    Rookie1 Addicted to ArboristSite

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    I think some dont know how to blip the trigger and get jiggy with it.:msp_ohmy:
     
  8. bobt

    bobt Addicted to ArboristSite

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    Yah, I know what you are talking about. When I worked in the saw shop we always used the impact wrench, but you have to set the "power" a little lower than you would use on a lugnut,,,Haha!

    I think most guys are afraid of shearing off the crankshaft or shearing off the flywheel key. The flywheel key was of no concern years ago when both the key and flywheel were steel. Now, from what I read here, the keys are cast in the flywheel and they are not steel anymore.

    Bob
     
  9. K5krawler

    K5krawler ArboristSite Operative

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    I even put them on with an impact!! SHHH don't tell anyone! You're right turn the power down and it works nicely.
     
  10. Rookie1

    Rookie1 Addicted to ArboristSite

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    Last edited: Jun 18, 2011
  11. roostersgt

    roostersgt Guest

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    Got it off. Left flywheel on during impact wrench treatment. Clutch assembly came off like a breeze with a little blip of the impact wrench. Piston is clearly toast. Cylinder wall looks and feels a little rough, not grooved, just aluminum transfer, I hope. I will try the muriatic acid wash tomorrow. I'm going to try to use aftermarket parts on this jewel. If the cylinder clean up, I'll probably order a piston and rings from Northwood Saw. If not, Ebay has a commie cylinder / piston / rings set for $43 plus shipping.

    How do you disconnect the piston from the connecting rod? Can't see any clip or anything to undo.
     
  12. K5krawler

    K5krawler ArboristSite Operative

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  13. bobt

    bobt Addicted to ArboristSite

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    Look carefully at the ends of the piston pin. There is a clip there that holds the pin in the piston. Carefully remove one of them by prying if necessary. They just love to fly around the shop, so be careful. I have put a plastic bag over the piston before, in case it flies.

    Then tap the pin out of the piston with a punch or even a screwdriver.

    Edit to add: Don't throw those clips away, as sometimes the new ones that come with the new piston don't fit snug enough, and the original ones might fit better. You don't want to assemble the engine with loose, sloppy piston pin clips. Just giving you a "heads up".

    Bob
     
    Last edited: Jun 18, 2011
  14. roostersgt

    roostersgt Guest

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    Thanks guys. I'll be checking closely for those clips and using the baggie trick. Good advice from all. What'd you think of the cylinder wall?
     
  15. K5krawler

    K5krawler ArboristSite Operative

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    Elbow grease and lots of it. Small wire brush with the acid, 220 girt and a dab of oil like I used to try to clean up my saw.
    Heck I even used a dremel with a wire wheel attachment to try to clean up the aluminum transfer.
     
  16. roostersgt

    roostersgt Guest

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    Stihl haven't gotten back to getting the dang piston off the connecting rod, but I did order a new piston / ring set from Northwood Saw along with 2 new oil seals. I'm betting, and taking my chances the cylinder will clean up.
     
  17. K5krawler

    K5krawler ArboristSite Operative

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    If you take a picture of the clip, we can probably edit the photo a bit to help you out.

    -K5
     
  18. roostersgt

    roostersgt Guest

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    Whew! Got that clip off. Only lost one of them. Tiny thing got lost in the dust on the shop floor. For some reason the picture uploader keeps failing when I try to upload additional pictures.
     
  19. K5krawler

    K5krawler ArboristSite Operative

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    Your new kit should come with a pin, two clips, piston and ring(s)
     
  20. roostersgt

    roostersgt Guest

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    You notice this model has no impulse line? No nipple, no nothing. Did I miss it somehow?
     

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