Engine Trouble Piston stuck in Cylinder; can I cut cylinder?

Discussion in '2-Stroke Engines' started by rjriggs, Aug 15, 2016.

  1. rjriggs

    rjriggs Member

    I can't get the piston out of the cylinder, and the piston is too far up in the cylinder for me to reach the wrist pin. I would prefer not to destroy the connecting arm because it's still good, and I would prefer NOT to split the case, which seems like it would take a LOT of time and patience. Is there some way to possibly cut open the cylinder? It's ruined anyway, as is the piston. Any ideas on how to do this if I can't get the piston out of the cylinder?


  2. MotorBicycleRacing

    MotorBicycleRacing Well-Known Member

    Use a piece of wood to pound your piston out of your cylinder.
  3. crassius

    crassius Well-Known Member

    also, taking all 4 head studs out may allow you to turn the cylinder a bit if a ring is stuck in port - some penetrating oil in there may help too
  4. butre

    butre Well-Known Member

    if brute force doesn't cut it I've had to cut a cylinder off an air cooled vw motor before. I do have a pretty nasty scar from the job, so take all the precautions you can. you ever see your own bones before? an angle grinder to a foot wearing flip flops can make that happen right quick
    Last edited: Aug 15, 2016
  5. rjriggs

    rjriggs Member

    Another question: if I cut the cylinder apart with a grinder...would I be better off splitting the engine apart to make sure no debris gets in the crankcase? If so, I may as well go the short route and just split the engine apart, no grinder necessary.
  6. crassius

    crassius Well-Known Member

    I wouldn't cut it because of fine debris that may never get completely cleaned out of bearing cages and big end rollers. I'd just get another motor rather than have it lock up again in a week.
  7. MotorBicycleRacing

    MotorBicycleRacing Well-Known Member

    How is this going to help you?
    If you split the engine the piston will still be stuck in the cylinder with no way to detach it from the crank.
  8. rjriggs

    rjriggs Member

    If I split the engine, I can remove the crankarm from the crank and cut the cylinder open outside of the engine, where I don't have to worry about about debris getting in the crankcase. It would also be a lot easier to cut it that way. I'm almost scared to ask: is it really that difficult to split the engine? There's a photo guide on this website that makes it seem relatively simple...and to someone with good mechanical skills, it probably is. This is the first engine I've ever worked on in my life. Of course, I bought my HT kit to learn a bit about working on motors. I just didn't expect my education to be completed so quickly.

    So -- if I can't buy another motor, should I split the engine, or try to cut the cylinder while it's still attached to the motor by the stuck piston? If I cut the cylinder while it's still attached, what's the risk of getting potentially harmful debris in the crankcase? (Pretty high, I'd imagine.) Or is it possible to remove the crankarm from the crank without splitting the engine? (I wouldn't think so.)

    By the way, thanks for the responses to my question. I really appreciate it!
  9. butre

    butre Well-Known Member

    if you're stuck at bdc you might be able to cram some paper towels in the case to prevent metal getting in there. otherwise just go ahead and cut and when you're done flush the case with gas a few times.

    the difficulty in splitting the case isn't so much in the process, but rather that they come with combo head screws and require more torque to undo than to strip.
    an impact screwdriver usually does the trick though
    sp1ke likes this.
  10. sp1ke

    sp1ke Member

    ok so your engine is blown and piston stuck my guess is youve unbolted your head chamber / jug is half way up threads so u can get to the crank but cant remove the top end due to the sieze

    what i would do next ( price up parts about 30 pounds here for a top end and instead buy whole kit for the tiny extra 65 and get lots of spares from my old engine )
    lets asume were going to try and repair it thou
    ascess the damage have metal fragments allready been flying around is the head / piston or chamber salvageable ( no )
    have fragments made it in to the bottom big end mainly its bearings ? most likely we can look at that later when the top end is removed for now some tissue / towel carry bag stuffed in there will stop anything else going down there

    step 1

    use wood to wedge under the chamber holding it up as far as u can get it and hammer the top of the piston down did this work if not
    if i can remove the 4 studs i will chances are u dont have a thread extractor but with the head off u can lock two or more nuts together allowing removal

    step 2
    realy pack that bottom end with a old towel to be certen to cover it well and stop fragments and we can cut the chamber down one side id use an angel grinder then pry it open with a crow bar slightly if needed
    and repeat step 1

    if its still not coming out id attack the opisite side of the chamber by then u know its off

    turn engine upside down remove towel clean up carefull not to get anything down there

    now its time to ascess the damage to the big end can you freely turn the crank can u feel any grittyness or does it stop entirely if its free your lucky it may be a tiny bit of grit u can wash out with spray lube
    lets asume the worst bearings need replaceing
    this means bottom end strip down if u know what your doing can be done in say 15 mins this engine is so simple im gonna teach my 7 year old about engines using one

    you will need philips screwdriver for screws behind the clutch housing / alan keys for most other bolts / flat head for the drive crank clutch bolt /and c spanners / sockets

    what u may need to buy is a clutch extractor tool if u dont have one allready rest are basic tools

    rather then carry on explaining from here to much ill show u some videos

    Steve Best likes this.
  11. Frankenstein

    Frankenstein Well-Known Member

    You know you can't remove the crank arm (connecting rod) from the lower end. Right?

    Single piece pressed with what has to be a hydraulic press. Unlike many friendlier motors you can't just unbolt 2 bolts and pull the arm and bearing out..

    I'd side with wd40 in the cylinder, remove the headbolts and twist the cylinder, it will let go quickly always does unless you physically melted the parts together. It will likely drop debris of some type in the engine, if they aren't already there, so clean it out with some gas to be safe.

    Either filter the gas with coffee filters or leave it dirty and keep in a metal or glass container in a safe place marked "gasoline" and use it to clean up all the hard parts that really need a good degreaser or use to clean just about anything when metal dust or chips are involved.