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Post by capob on Jun 20, 2016 17:55:23 GMT -5
Hi
I have a 50cc 2 stroke scoot which ran completely fine until the crankshaft got jammed.
I disassembled the cylinder but broke the piston rings, I got new 2 new rings from the dealer and installed them but the crankshaft was still stuck. I got the scoot to the dealer and he found that the piston bearing shattered and a piece got stuck between the crankshaft and the crankcase. He replaced the bearing, spark plug, vario pulley, vario nut, reed valve and head gasket.
Now the scoot doesn't run like before.
-It uses more fuel
-It doesn't accelerate as powerful as before
-The exhaust gets extremely hot
-After a while riding the scoot bogs down to idle and stays there, it won't react to throttle anymore until it idles for approx. 30 seconds.
Any tips or advice would be very welcome
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Post by pistonguy on Jun 21, 2016 6:22:18 GMT -5
Would have really liked to look at the Piston and Cylinder Bore.
Especially since you mention you broke the rings.
Was that the Top Rod Bearing or the Bottom End Crank Pin Bearing? this is important
With the Bering taking dump, pieces parts like to go up thru the transfer ports and make a mess.
That Piston and Bore Condition is the life boo of the Two Smoker.
Picture say a thousand words,
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Post by lain on Jun 21, 2016 11:32:31 GMT -5
The way it sounds the piston rod may be mis-shapen now, and/or possibly wrong piston ring positions... Sounds like it's overheating... Honestly the way it sounds if you don't want to pay your mechanic for practically a new scooter just buy a new engine drop-in. They sell them on ebay for about 300-400. Make sure to get the one that fits your frame, pay attention to the rear end of the drop-in engine, make sure the engine is identical to your current one.
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Post by capob on Jun 21, 2016 13:00:26 GMT -5
Both piston rings were broken, I got a new set and installed them.
With the new set there was a third smaller and very flexible ring but I didn't recall removing a third ring.
After the replacement of the rings I saw in the service manual there should be something under the bottom piston ring. Could the lack of that extra ring be the cause of the problems?
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Post by lain on Jun 21, 2016 14:11:44 GMT -5
Every ring is entirely essential and the placement and position of each of them is crucial.
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Post by pistonguy on Jun 21, 2016 16:56:44 GMT -5
Duuuuudes, Its a TWO STROKE! It has only Two Rings that are Located by Pins in the Piston (ring locating pins). These Locating Pins Stop the Ring From Rotating and Opening Up the Gap in a Port i.e. Snag or Hang a Ring. It is Possible to Install the Ring Over the Pin and with Force the Cylinder Down, This Pushes the Locating Pin Into the Piston and the Ring Hangs on a Port and You go Over the Bars. Here is a KX250 Cylinder showing the Ports that you Don't want the Ring opening Up Into. I should also mention that these Devil Pins can come out for several reason's and you Snag a Ring. When and if they come out the Pin itself either jams itself between the piston and cylinder or goes put top the piston and beats around there for awhile. Its a pretty sight    |
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Post by pistonguy on Jun 21, 2016 17:00:19 GMT -5
I would like to know more on How you think or what did you find with Your Broken Rings. Do you still have the broken rings to post a picture? Most of the time its Hard to Break one outhouse rings unless it some old school Ductile Iron.   This is what I can do with My Rings. |
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Post by capob on Jun 22, 2016 7:58:34 GMT -5
pistonguy i'm very sure it's a two stroke however this is in the service manual:   Also, my rings aren't flexible at all, I broke this pair while trying to reinsert the piston in the cylinder. 
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Post by pistonguy on Jun 22, 2016 15:57:50 GMT -5
pistonguy i'm very sure it's a two stroke however this is in the service manual: Also, my rings aren't flexible at all, I broke this pair while trying to reinsert the piston in the cylinder. Note: my picture of the ring shows the Same Notch at its ends. Your Rings have The Same Ground In Notch to Go Around the Ring Retaining Pins. Check to make sure the Pins ar in the Piston, The Ring on the Left looks Like the End Notched for the Pin is In Bad shape/almost gone/unusable even if you got them in the bore. I'd really like to see the piston, I think you got a pin problem and those rings are hanging (opening up) a port. They Do Show a Expander Ring Under the Second Ring, That is Really Rare. Missing Will not cause you to be snagging rings upon installation |
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Post by pistonguy on Jun 22, 2016 16:04:28 GMT -5
Something else.
Those Ring Retaining Pins in the Piston are almost always on the Intake Side of the Piston.
The Big exhaust port is on the other side so never pined there.
There should be a Arrow on the Dome of the Piston pointing towards Exhaust, if you put it in backwards the rings open up in the exhaust port and you will break them every time. looks like your opened right up in a port.
You may have that piston in there backwards.
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Post by capob on Jun 22, 2016 16:45:32 GMT -5
I broke broke the ring because I didn't knew about pins at that time and the rings were not aligned with pins, this made sure the rings broke when I forced them into the cylinder.
I don't have the space at home to open up the engine but whilst looking at the underside I noticed the head gasket was sticking out for 2-3mm. Is this normal or could it contribute to the power loss I face daily?
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Post by lain on Jun 23, 2016 8:18:38 GMT -5
I broke broke the ring because I didn't knew about pins at that time and the rings were not aligned with pins, this made sure the rings broke when I forced them into the cylinder. I don't have the space at home to open up the engine but whilst looking at the underside I noticed the head gasket was sticking out for 2-3mm. Is this normal or could it contribute to the power loss I face daily? Yes, if you aren't replacing your gaskets when they get worn they could be blown out from pressure and causing vacuum leaks which also cause serious overheating and possibly soft-seizing of the engine. I replace mine every single time I open my engines up, no chancing it for me, but you may be able to get by and be fine with 2strokes as long as you don't scratch it or bend it and as long as you install it exactly as it was before, but it sounds like you reinstalled it and now it's protruding from the engine underneath? |
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Post by capob on Jun 23, 2016 15:52:35 GMT -5
lain When I installed it it wasn't protruding from the sides, since the dealer replaced it it sticks out. I ordered a new gasket and piston rings, they should arrive next week, I hope that fixes the problem. 
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Post by pistonguy on Jun 23, 2016 16:19:11 GMT -5
I broke broke the ring because I didn't knew about pins at that time and the rings were not aligned with pins, this made sure the rings broke when I forced them into the cylinder. I don't have the space at home to open up the engine but whilst looking at the underside I noticed the head gasket was sticking out for 2-3mm. Is this normal or could it contribute to the power loss I face daily? You state "head gasket" that is the gasket on Top. The base gasket is on the Bottom of the Cylinder. Head gasket for sure? Some gasket can hang out some but the inner and outer most of the time matches. We really need to look at those Ring Retaining pins, That you were able to Break Rings upon installation tells me the Pins, Ring Grooves and Piston may be Buggered up. Take and post allot of pictures, I can do allot more with pictures. Just for example this is a Two Stroke Cylinder upside down so that is were the Base Gasket goes.  |
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Post by pistonguy on Jun 24, 2016 6:20:45 GMT -5
I broke broke the ring because I didn't knew about pins at that time and the rings were not aligned with pins, this made sure the rings broke when I forced them into the cylinder. I don't have the space at home to open up the engine but whilst looking at the underside I noticed the head gasket was sticking out for 2-3mm. Is this normal or could it contribute to the power loss I face daily? Yes, if you aren't replacing your gaskets when they get worn they could be blown out from pressure and causing vacuum leaks which also cause serious overheating and possibly soft-seizing of the engine. I replace mine every single time I open my engines up, no chancing it for me, but you may be able to get by and be fine with 2strokes as long as you don't scratch it or bend it and as long as you install it exactly as it was before, but it sounds like you reinstalled it and now it's protruding from the engine underneath? I was really hoping you would back off and let me help this guy as not to confuse and miss direct. Just gets plane silly, You replace Your Gaskets Every Time. No Chancing it for You? Huh? since when?. when I came on this board your posting threads of oil pumping outa base gaskets, stated you reuse them all the time and Advocated it to others, and Your doing it again to this guy, Do you even understand "Gasket Crush"? Then with your Vast experience had to be school that you torque the Cylinder Studs So many times they will No Longer Stretch and your Drawing up metal from the Top of the Block. Ya had to Get some good Taida Studs. Beginner stuff. Room #101 Cylinder head torque, again you actually admitted to Never Owning or Using a Torque Wrench but you have a Very Good "Feel" for Torque. Really? Vast experience again huh? Your Calibrated Elbow couldn't show me the difference between 22"lb and 32"lb's Then your throwing a new set of rings in (all new to you) and learn Ideally you Should make a few passes with a Good Cylinder Hone to break any glaze and Seat in the new rings. You stated Don't own one never used one, and don't own a drill. oh ok, then you actually admitted to using something by Hand, Seriously? Stated what a beautiful job it was but you have No Pictures of the job (thats a norm). How could you know if it was a good job since you Never have used one and did not have something to compare your work too. You can't, just plane silly Half a week or so for you to figure out what Metric Allen Head removes the Top Cap nut off your Fork tubes. you called them shocks. The big tear down was to remove the nut and wash out with Seafoam , are you familiar with the packing materials in the fork that the Strong Aromatic Petroleum Distillates contained in Seafoam may Not Agree with? Materials in there are Not the Same as in carb's that Seafoam is safe in. How bout your rear shock fiasco? Vast experience have 0 understanding of "Spring Rate" were completely puzzled by not being able to make it work. Now Your on here Stating a shop brings you in as expert consultation and your Critiquing other so called Technicians. You advertise you create custom sig's but Never have Any Pictures of Anything You do or of Your Scooter. Back to this 50cc two stroke. These 50cc two strokes are so sensitive to air Leaks if he puked or sucked a base gasket she Wont even run. A "Soft Seize" is a generality, is Nothing Specific and the Verbiage is Not used in the Industry. You have "0" experience with two smokers and Any type of Seizure in Any Engine for that matter. You couldn't tell one type of seizure from another.   |
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