Fitting pistion ring bought the wrong one

  1. angellonewolf

    angellonewolf Member

    Messages:
    3,955
    Location:
    bristol england
    Ok in sure I've posted a thread on a hedge trimmer a while ago

    It's been sat in a corner for a while after a head rush and mix of beer one night I found what seamed to be a good details on the bore size and after beer googles measure of the bore i bought a cheap China copy

    Now this may sound daft but it's a try as I've had a generator for a couple of years that I've kept around until my garage was done so if this works I could possibly do the gen at a later date

    Now pics of the ring as it's in the bore as can be seen about a couple mm to big

    20190711_191301.jpg 20190711_191337.jpg 20190711_191355.jpg

    Now this needs to be cut down to the right size how much gap should there be between the 2 ends of the ring and the pistion has a round pin in it how do I make it fit and what sort of torralance do I need to worry about

    Can I just remove the pin ? That would make it a lot easyer ? Or I'm assuming it there to stop the ring from spinning around ?
     
  2. mechman Member

    Messages:
    1,607
    Location:
    great britain n.e.lincs
    It's there to keep the ring in its right position.
     
  3. angellonewolf

    angellonewolf Member

    Messages:
    3,955
    Location:
    bristol england
    yea though as much

    can i cut the new ring and any way i can make the round bit in the ring
     
  4. angellonewolf

    angellonewolf Member

    Messages:
    3,955
    Location:
    bristol england
    15628710109051890685529658802161.jpg idea?
     
  5. Pete.

    Pete. Member

    Messages:
    7,959
    Location:
    Kent, UK
    You can file the ring, and file the round bit with a small round file. Some sort of guide will help.

    That piston is shot though.
     
    Last edited by a moderator: Jul 11, 2019 at 9:03 PM
  6. premmington

    premmington Member

    Messages:
    960
    Location:
    Norfolk
    +1 for the above.

    I would want to know why as well - have you checked the con rod bearings - upper and lower?
     
    Last edited by a moderator: Jul 11, 2019 at 9:03 PM
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  7. angellonewolf

    angellonewolf Member

    Messages:
    3,955
    Location:
    bristol england
    yea i know the the piston is shot but a clean with 5000 wet and dry will allow me to try and hope make it last for a little while as a test for the honda generator

    the piston is scored as the old ring got stuck in the piston theres not movement in the bottem end im assuming the person used the wrong fuel mix ? it was blackend ived give it a little clean to get there but only removed the coke so i could remove the ring
     
  8. pedrobedro

    pedrobedro Man at Matalan

    Messages:
    9,514
    Location:
    CX Derbyshire
    That piston is shot, you are wasting your time trying to fit a ring to it and expecting any compression. 5000 wet and dry ? You might get a polish on it but it's not going to shift those grooves. If you take the grooves out of the piston it is going to be well under size. The piston is grooved because it stuck to the cylinder wall due to excess heat I've seen it many times in chainsaws.
     
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  9. gordon stephenson

    gordon stephenson Forum Supporter

    Messages:
    6,273
    Location:
    Skelton in Cleveland U.K.
    Piston well scored, as you know, pin stops ring rotating so that the ring ends are kept away from the ports, rings are easily filed.
     
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  10. angellonewolf

    angellonewolf Member

    Messages:
    3,955
    Location:
    bristol england
    But round it's only 1.5mm thick does it have to be exact round or just stop it ?
     
  11. Robotstar5

    Robotstar5 Casanunda Staff Member

    Messages:
    17,548
    Location:
    Birmingham
    Rule of thumb is .004" gap per 1" of bore on air cooled engines.
     
  12. angellonewolf

    angellonewolf Member

    Messages:
    3,955
    Location:
    bristol england
    ^^^^ that diameter or circumference of the bore
     
  13. Fintray

    Fintray Forum Supporter

    Messages:
    766
    Location:
    Aberdeenshire (UK)
    Diameter.
     
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  14. Sean Another 602 fan

    Messages:
    1,052
    Edinburgh
    Wile i admire your have a go spirit....really you need to chuck most of this in the bin and learn not to buy stuff off the internet while under the influence!
     
    eLuSiVeMiTe, dobbslc and Robotstar5 like this.
  15. frank horton

    frank horton V twins are great but 4"s rule.........

    Messages:
    1,281
    Location:
    Soon 2 B Crete
    looks like a lost cause to me......
    in the old days we had to size the rings quite often.....we just did it carefully on the grinder.....
    with the state of the piston and who knows what the bore and the port edges look like it might run all of 2 mins......

    just have a few more beers and bin it.......hahaha
     
    angellonewolf likes this.
  16. angellonewolf

    angellonewolf Member

    Messages:
    3,955
    Location:
    bristol england
    the bore is suprisingly clean if you rub your finger round its clean from marks or i would not have considderied it
     
  17. Screwdriver

    Screwdriver Member

    Messages:
    4,729
    UK London
    Piston ring will be surprisingly soft and "easy" to file. You need a very small diameter jewellers or needle file. It needs to fit as close as possible to the spec for your engine remembering there's a lot of heat in there and if you get that dimension wrong, the ring will expand anyway but with nowhere to go. It is vitally important that the ring does not rotate or the gap will dive into a port leading to rapid unscheduled disassembly.

    It will also be very easy to break being made from cast iron but it should work. Assuming no major damage to the bore you need to hone it to get rid of any piston that might be smeared in there or the piston will seize in an instant. Similarly, run a file around the lip of the ports to make sure there's no sharp edges, just soften the edge, don't chamfer it. If the ring doesn't break up immediately, it will probably run for hours. Won't be perfect but it' surprising what you can get away with.

    So while you can "get away with it" the writing is on the wall and it's only a question of time before catastrophic failure. Could be tens of hours though so if it gets you out of a jam, you have nothing to lose.
     
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  18. pedrobedro

    pedrobedro Man at Matalan

    Messages:
    9,514
    Location:
    CX Derbyshire
    You can usually salvage the cylinder with some brick acid to remove the piston residue then rub it with some 240 grit and WD40 to finish it off and hone it a bit but the Nikasil finish is surprisingly tough.
     
    angellonewolf likes this.
  19. zeppelin builder

    zeppelin builder Member

    Messages:
    1,066
    Location:
    peoples republic of scotland
    as stevie wonder quoted
     
  20. daedalusminos Member

    Messages:
    563
    Location:
    Norwich
    That piston is truly ugly....the ring clearance in the piston groove (top/bottom surfaces) is also toleranced...typically 25-75um on a 4-stroke
     
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