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Piston, ring and liner. How to tell when they're toast

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  • #1

    Piston, ring and liner. How to tell when they're toast

    Is there a good rule of thumb for being able to tell when a piston or liner is just shot or can be salvaged?

    Yesterday I had a strange thing happen, the engine started fine and ran well for a couple minutes, plenty of smoke and everything, then it suddenly warbled a bit, dropped in rpm, so I brought it down to land. I couldn't land imediately as I had to wait for a plank that was landing but I was just hovering, nothing strenuous. Anyway, I landed and the engine cut after idling a bit. When I took it over to the pits it had almost no compression and would not start again.

    So I pulled the piston and liner out today and the ring is stuck in the piston on one side and the piston and liner both have some visible scratches in the area where the ring is stuck down.

    I don't know at what point a scratch in the liner is too deep and it's a goner or if it would be OK with just a new ring.

    Is it possible to have a liner honed smooth again if the scratches are light enough?

    The engine is an OS91HZ-PS and I already know that the cost of the piston, ring and liner together would exceed the cost of an entire 2nd hand engine.
    Kasama, Minicopter, Henseleit, JR, Shape, Beam
    Robbe, RMJ Raptor gasser, powered by
    Spartan, Spirit, BeastX, Kontronik, CY Total-G, DX8
    member of Epsom Downs and Bloobird clubs
    Proud recipient of 7 EGS! and a platinum star
    Tags: None
  • #2
    I have had the piston ring stick too the piston twice now causing them not too start and no compression after a spell on the shelf...I put it down too the after run oil I have I think it must have castor oil in it...i would put another ring on it hone the liner and give it a go.....
    Heli central...Basildon RC helis...strictly helis only...




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    • #3
      Have you got some hi res pics Sheryl
      Some say my left nipple is the shape of a Raptor canopy.......... And that for fun I chase sheep in wellies 3 sizes too big. All I know is I am ​3D Clod
      Very proud to be a Presenter on ROTORS! The RC Helicopter show


      Very proud to be a 2x EGS winner

      Collector of SAB Goblins

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      • #4
        Same thing happened to my os50 few weeks ago! Sounded lovely in the air, plenty of smoke, and then silence My very first forced auto of inverted and I land it better than I had landed with power on! lol
        Anyway, loss of compression, striped engine and found ring stuck in the liner. Damage to the liner way too much.

        If you can get hold of a brake wheel cylinder honing tool, worth a go to see if you can remove as much as you can.

        http://www.snssafety.co.uk/brake-cyl...2355abb503455b
        Last edited by panosg; 24-04-2013, 05:26 PM.



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        • #5
          Originally posted by KevDavies View Post
          Have you got some hi res pics Sheryl
          I'll take come pics and see if they're detailed enough to judge.

          I think the piston is OK as the scratches are very light, with the Liner I can feel the scratches with my fingernail but I don't have a point of reference to judge. It's just an area about 3cm across where the ring stuck into the piston. I know if there was a deep trench it would be toast.

          The ring definitely has to be replaced but that's not a big deal.
          Kasama, Minicopter, Henseleit, JR, Shape, Beam
          Robbe, RMJ Raptor gasser, powered by
          Spartan, Spirit, BeastX, Kontronik, CY Total-G, DX8
          member of Epsom Downs and Bloobird clubs
          Proud recipient of 7 EGS! and a platinum star

          Comment

          • #6
            Actually, looking at it closer now I think the piston is probably dead because there is material rubbed into the oil slot below the ring, so it would need some work to salvage it.

            The liner, it's hard to say and I don't think you can tell from a photo as it's just not an easy thing to photograph. To me it feels like it might be possible to hone it out (which is not something I could do anyway so probably a moot point).

            IMGP5272.jpgIMGP5269.jpgIMGP5270.JPG
            Kasama, Minicopter, Henseleit, JR, Shape, Beam
            Robbe, RMJ Raptor gasser, powered by
            Spartan, Spirit, BeastX, Kontronik, CY Total-G, DX8
            member of Epsom Downs and Bloobird clubs
            Proud recipient of 7 EGS! and a platinum star

            Comment

            • #7
              Piston, ring and liner. How to tell when they're toast

              We've done some similar repairs on engines recently - a chap on eBay does replacement rings for around £10 depending on engine and they work well. Minor scratches etc hasn't stopped our engines from working again - but make sure the piston looks ok, especially the groove the ring sits in - dont want it sticking again.
              Removal of the siezed ring can be easier if you heat the piston up first.

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              • #8
                If it was me Sheryl they would be heading binwards. It looks a bit too far gone. You could try a light hone and a new ring, but Id say that was too far gone for it to be worth a shot.
                Some say my left nipple is the shape of a Raptor canopy.......... And that for fun I chase sheep in wellies 3 sizes too big. All I know is I am ​3D Clod
                Very proud to be a Presenter on ROTORS! The RC Helicopter show


                Very proud to be a 2x EGS winner

                Collector of SAB Goblins

                Comment

                • #9
                  If you can feel it with your finger nail I would say it is toast..you only hone it too remove the glaze not any liner material....
                  Heli central...Basildon RC helis...strictly helis only...




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                  • #10
                    Originally posted by Pabs View Post
                    We've done some similar repairs on engines recently - a chap on eBay does replacement rings for around £10 depending on engine and they work well. Minor scratches etc hasn't stopped our engines from working again - but make sure the piston looks ok, especially the groove the ring sits in - dont want it sticking again.
                    Removal of the siezed ring can be easier if you heat the piston up first.
                    Well it's a shame if it's just an awkward paperweight now.

                    Speaking of engines, have you done anything with that OS46 yet?
                    Kasama, Minicopter, Henseleit, JR, Shape, Beam
                    Robbe, RMJ Raptor gasser, powered by
                    Spartan, Spirit, BeastX, Kontronik, CY Total-G, DX8
                    member of Epsom Downs and Bloobird clubs
                    Proud recipient of 7 EGS! and a platinum star

                    Comment

                    • #11
                      get the parts from Japan I think they will work out cheaper for you....
                      Heli central...Basildon RC helis...strictly helis only...




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                      • #12
                        Originally posted by KevDavies View Post
                        If it was me Sheryl they would be heading binwards. It looks a bit too far gone. You could try a light hone and a new ring, but Id say that was too far gone for it to be worth a shot.
                        Yeah it would seem that's probably the case. I have an OS 91 SZ I can put in there but I was keeping it for spares as I have an SZ in the Dyna-X. I still have the SX C-spec currently in the Raptor but I think I would want to remove the pump. Last but not least I do have an old YS91ST I got with an airframe and have never run. But the bottom line is that anything I put in this heli has to be reliable because it is not cheap to repair in the event of a forced auto that isn't totally smooth.
                        Kasama, Minicopter, Henseleit, JR, Shape, Beam
                        Robbe, RMJ Raptor gasser, powered by
                        Spartan, Spirit, BeastX, Kontronik, CY Total-G, DX8
                        member of Epsom Downs and Bloobird clubs
                        Proud recipient of 7 EGS! and a platinum star

                        Comment

                        • #13
                          Originally posted by trillian View Post
                          Well it's a shame if it's just an awkward paperweight now.

                          Speaking of engines, have you done anything with that OS46 yet?
                          Hey - yeah, did you not see my post? Posted up a big thank you, and a post in the recommend for an EGS thread
                          The OS46 runs perfectly - as with all OS 46 engines there is a slight dead-spot when cold, but this soon goes and the engine runs flawlessly! It's now in my raptor 50 - I've done the full 30-50 upgrade and am very happy
                          Also had the OS 32 running on the bench - also ran perfectly after a little tweaking. It is hopefully going in a 30-size Hirobo Jet Ranger of my dads - saves him cutting into the fuselage for a top start..
                          Thanks again

                          Back on topic now Sorry for the mini-hijack!

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                          • #14
                            Originally posted by Pabs View Post
                            Hey - yeah, did you not see my post? Posted up a big thank you, and a post in the recommend for an EGS thread
                            The OS46 runs perfectly - as with all OS 46 engines there is a slight dead-spot when cold, but this soon goes and the engine runs flawlessly! It's now in my raptor 50 - I've done the full 30-50 upgrade and am very happy
                            Also had the OS 32 running on the bench - also ran perfectly after a little tweaking. It is hopefully going in a 30-size Hirobo Jet Ranger of my dads - saves him cutting into the fuselage for a top start..
                            Thanks again

                            Back on topic now Sorry for the mini-hijack!
                            No I didn't see that. I'm so glad to hear it runs well!
                            Kasama, Minicopter, Henseleit, JR, Shape, Beam
                            Robbe, RMJ Raptor gasser, powered by
                            Spartan, Spirit, BeastX, Kontronik, CY Total-G, DX8
                            member of Epsom Downs and Bloobird clubs
                            Proud recipient of 7 EGS! and a platinum star

                            Comment

                            • #15
                              If you can feel the scratches it sounds pretty toast ...

                              I had a piston ring stick to the piston after a few months of non activity, pain in the ass.. No compression, wouldn't start and had to dremel it out in the end after trying many other ways...

                              No after run oil and no castor oil + Engine is always run dry of fuel at the end of the day. I think it was either a dodgy ring from the factory or you just really have to run these engines at least once a month...

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