Piston Stuck

Discussion in 'Motorized Bicycle General Discussion' started by lowaus, May 23, 2014.

  1. lowaus

    lowaus New Member

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    Hi so today i got my pistons rings on my piston because when i ported the engine one of the rings snapped, so i checked everything and the rings are the right ones. when i put the cylinder on(had to use a lot of force) the piston was stuck, wouldn't move at all, also got them compressed between the grooves.
    After 30 minutes of not getting my bike to start, i took off the cylinder and their was small metal shavings all around. Does this mean i need a new cylinder.
     
  2. soup325

    soup325 New Member

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    Im just wondering if you reinstalled the piston facing the way it came out?

    A handy tip I picked up here, was to always mark a forward arrow on the piston.

    it depends on how bad the cylinder wall has become. you can try to reinstall it. but i would do a compression check. just to check you have no leaks or very small ones.
     
  3. lowaus

    lowaus New Member

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    Hi i never took the piston out to install the rings, and the piston already has a arrow on it. Also their are no marks on the cylinder as well, no chipping, no nothing.
     
  4. mapbike

    mapbike Active Member

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    My question is how did you install rings on your piston without removing it from cylinder?

    Did you wipe down piston and cylinder bore with 2 cycle oil before attempting to install piston?

    If it was stuck in cylinder and you found metal shavings then then you have "big trouble in little china"

    The retainer pins that are in piston that prevent rings from rotating should always be on the intake/ carb side of the engine, if your piston was stuck in the bore and has shaved metal then I can almost guarantee that you didnt have the rings in the correct position and Im still trying to figure out what you mean when you said you didnt remove the piston to I stall the rings......
     
  5. lowaus

    lowaus New Member

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    I removed the cylinder head and cylinder and then took out the studs to put on the rings.
    Yes i did wipe down everything,(actually left the 2 stroke oil on every part of the top end.
    Also the rings were on the right part of the piston when i installed the cylinder but the force of the hammer might have moved the rights out away from the pins.
     
  6. Toothy

    Toothy New Member

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    Sounds like the rings were not seated correctly in the grooves during install. No expert here but I didn't use a hammer to put the cylinder back on. Sounds like you forced it and caused the damage when you cranked it over.
     
  7. Kioshk

    Kioshk Active Member

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    Oooohhhh...still a bit sketchy on what you did, and why the rings were removed to begin with. Was this a broken-in engine? If so, I've had trouble in the past reinstalling old/new rings on a used piston: the minimal carbon build-up can prevent the rings from reseating properly, and result in their being a slightly larger resulting diameter than the cylinder. You should NEVER have to force the cylinder over a ringed piston with any more force than some light taps of your palm. NEVER use a tool to do this, ESPECIALLY a hammer. You may still be able to recover. I have actually run temporarily on one ring while I awaited replacements. Post some pics!

    If it IS indeed carbon-buildup caused interference, use a new, sharp razor-blade to scrape the carbon off the old-rings and the piston's ring-grooves until rings can easily be compressed manually so the rings' outer faces are flush with the piston's.
     
  8. 2door

    2door Moderator
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    I'm guessing the OP didn't have the ring gaps aligned with the retaining pins in the grooves. If they are not aligned the cylinder can be 'forced' down over them but you'll end up with what he has; a piston that won't move in the cylinder.

    Tom
     
  9. Davezilla

    Davezilla New Member

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    Sounds to me like the ring rotated so the pin wasn't at the gap anymore, You'll feel that installing the cylinder because it'll stop dead and not go down any further. If you can't get the jug to go down over the piston with gentle hand force, it's time to stop and see where the rings are.

    I can agree with the carbon build up theory too if the engine has been run for a good amount of time and the best way to clean the ringlands is with a section of broken ring as a scraping tool, then gently scrape it out, if the carbon is really stubborn, get a gallon of Berryman B9 Chem Dip at an auto parts store and soak it for about an hour. I've used the same gallon of B9 for almost 6 years as it's one of the best carb cleaning dips out there, and it lasts and lasts. After a good soak in the dip the carbon will still be there but will be loose enough to clean off easily, and it'll clean out a gummed carb like new easily if you ever let the bike sit too long and forgot to drain the carb so if you do buy the stuff it won't go to waste...

    You can run on one ring while waiting on parts as long as the cylinder bore isn't scratched, I've done it too... These rings do have a lot of end gap tho so you may or may not experience a power loss, mine ran fine on top but not so fine at low rpm on the single ring.
     
  10. crassius

    crassius Well-Known Member

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    I've seen some over-sized pistons around out there, but they're usually marked with a number (seen 1 thru 4 so far). Mic-ing them, I'm thinking each number is 20 micrometers larger, so a number '4' is 80 micrometers larger than stock.

    I'd first try to install the piston with no rings to be sure it fits.
     
  11. Davezilla

    Davezilla New Member

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    I've never mic'd my pistons before but is that what the numbers mean? I've seen them marked 1-5 as well and both mine have #2 marked on them.
     
  12. CTripps

    CTripps Active Member

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    If you need to use a hammer or mallet to slide the piston into the jug, something's not right.

    Getting the piston in there can be a tricky thing.. I slide the jug down the studs to meet the piston (at about half-way between top and bottom of stroke, that gives me room to move the piston instead of the jug). With one end of the top ring against the pin in the groove, work around the ring compressing it into the groove while keeping enough pressure on that as soon as it can, it slides into the bottom of the jug. The hardest tools I use for the job are my thumbnails. Gently push/wiggle it in until you can repeat with the second ring (which, for no other reason than "because I do", I go the opposite direction around the piston positioning it the same way). Once both are in, you should be able to seat the jug against the bottom end and move the piston by turning the nut on the magneto shaft.
     
  13. mapbike

    mapbike Active Member

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    If a hammer had to be used to force jug over piston rings were not aligned right most likely, all it takes is a little pressure around the ring with your fingers as you apply just a small amount of downward pressure on the jug and piston will easily slide into jug.

    As far as needing to mic the piston goes I have never seen or heard of anyone coming across a china girl piston that was oversized, I've got them with #2 marked on them #5 marked on them nothing atall marked on them and every single one has always been 46.90mm + up to 47mm for the 66cc pistons never had one that was larger than that, im gonna honestly venture to say that isn't a concern.

    Im gonna say all the parts and pieces were just fine and the problem was that installation wasn't done as it should be, I've put an older piston in a new jug with new rings, new piston in older jug with used rings as well as new rings and never had an issue and all the engines ran just fine, the thing that needs to be understood with these engines that have a chrom d bore is that the cylinder wall does very little "seating in", with a light cross hatch hone, the rings actually wear in to the cylinder wall not the opposite, the chrome plating is way harder that the iron rings so the rings conform more to the cylinder than the opposite.

    Judging from what I have read here Im set on the fact that this entire issue is an incorrect installation problem not an issue with the components.

    If jug doesn't have any deep gouges in it and piston ring grooves aren't damaged, and the little retainer pins aren't driven into piston, this should be an easy fix, but im guessing retainer pins could be damaged now and if jug bore is deeply scratched 3/4" above the very bottom of bore I'd say new jug, piston and rings will be needed and then it needs to be installed right to resolve the problems and get this engine back to at least running condition.

    Map
    .wee.
     
    #13 mapbike, May 23, 2014
    Last edited: May 23, 2014
  14. crassius

    crassius Well-Known Member

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    I've seen a #4 piston start & run, but get tight once the engine warms - 80 micrometers is just about 3 thousandths of an inch
     
  15. 2door

    2door Moderator
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    I just remembered an engine that was returned to a vendor with a "stuck piston". The customer did not disassemble anything but he said "the engine was seized". When I took it apart I found a ring alignment pin was out of its hole in the groove and wedged under a ring. The engine was indeed, seized. The assembler at the factory had managed to get the piston into the cylinder but it was jammed at BDC. Luckily the customer did not try to force anything and the engine was never started. I was able to salvage everything except the piston and that engine is the one on the Captain American bike today. Runs great.
     
  16. lowaus

    lowaus New Member

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    Thanks for the help guys, ill try do this today.
    The engine isn't broken in, it has around 70 miles on it.
    Before installing the rings i did a run with the cylinder and piston. The cylinder went on real easy without the rings on the piston. I do have 2 broken motors, with either some missing parts, could use them for the for the piston and could use the cylinder of it, the 2 motors that are broken seem to have a heavier looking connecting rod.
     
  17. lowaus

    lowaus New Member

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    Alright so i made sure the rings were aligned and everything no hope. I installed the cylinder on with the piston at bottom dead centre and it seems to always stop moving at the inlet ports. i tried this with 3 different cylinder, and it was always the same results
     
  18. mapbike

    mapbike Active Member

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    Dude I dont know what to telll you at this point... I have never heard of the issues you're having, but I can say that if the piston is in good shape, the jug is in good shape and you are getting something binding up, its got to be something else in the lower end of that end causing the problem.

    Take the piston off of the connecting rod and install it with rings on it into the cylinder and with the handle of a hammer or a piece of a old broom handle or something simular slowly push the piston up into the cylinder and all the way out the top, if it slide through without getting hung up, then that aint your problem.

    Map
     
  19. crassius

    crassius Well-Known Member

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    if you have the barrel wrong way 'round the ring may hang in the exhaust port (which you will be thinking is intake port)

    if the piston isn't too big, I can't think of any other case that will hang it
     
  20. lowaus

    lowaus New Member

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    So i got the same jug and everything on another engine, so il just fix one of my broken engines and use the new one for parts
     

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