an unusual engine seize

Discussion in '2-Stroke Engines' started by arkives1, Feb 11, 2011.

  1. arkives1

    arkives1 Member

    Last fall I was riding one of my bikes when it suddenly came to a screeching halt. I soon discovered that the engine was seized. I couldn't think of why since I'm very careful about oil/gas mixture. I took the centrifugal clutch off, and learned that the drive sprocket and dry clutch worked perfectly, the problem was within the case somewhere. I took the engine off and put a different one on and set that one aside for winter projects. I finally got to it today. I had removed the dry clutch and turned the engine over to remove the magneto in preparation for opening the case up. When I took a close look at the magneto I found a thin star washer jammed between the rotor and the stator. I removed the nut from the rotor and loosened the screws holding the stator. With a small brass rod and a light hammer I was able to tap the rotor around and get the washer out. I was scratching my head on where the heck did that thing come from. Finally it hit me, there had been a pull starter on it. Sometimes when putting a pullstarter on these things a couple of washers are needed to space the cup out a bit to clear the stator screw heads. Apparently I had dropped one and didn't notice it. I had put the puller on and was riding the bike quite a long while before it locked up. The washer must have been down in the bottom of the magneto cover somewhere and I didn't see it. It finally vibrated up into the rotor which quickly latched on to it magnetically and promptly fed it into the narrow space between the moving parts. I was relieved to find that the engine was not damaged after all. It never occured to me to look at the magneto to see if it was free or damaged, after all I had removed the pull starter and would have seen any damage wouldn't I? Obviously not! Just something to keep in mind if I ever have another engine seizure. It doesn't have to be a major breakdown to stop these little beasts.

  2. Skyliner70cc

    Skyliner70cc Active Member

    Unfortunately, I had a seizure yesterday. A piston ring was catching a port. I didn't follow my own advice on new builds and didn't JB weld the tiny ring keeper pin on this engine. The pin was missing (the hole was laterally elongated) and my head has some nice gashes in it. Fortnately, I have about 1/2 dozen spare heads and piston lying around and was able to the engine running again in less than an hour. This engine had less than 4 hours on it and I'm glad it happened riding around the neighborhood than on a long ride away from home and away from civiliazation.

    If this happens in the "field" and you carry a good toolkit with spare parts, the easy fix it to remove the broken ring and run the engine on a single ring. You won't have much power but it'll get you home. This is probably the only time I'd recommend using 20:1 oil mixture ratio ;-) How do I know this? About 6 years ago, I got an engine from a well known vendor that had only one piston ring on the piston. It was harder to start and ran but it wan't good for more than 12 mph on a 44 tooth sprocket. I rode it for an hour and when it didn't generate as much power as I thought it should, I tore it apart and discovered the missing ring.
  3. jaguar

    jaguar Well-Known Member

    Yeah, single ring pistons are for high revving engines whereas these are low rev engines
  4. HeadSmess

    HeadSmess Well-Known Member

    :cool:i gots me some triple ring 2-stroke pistons:cool:

    yeah, a bit big, theyre out of a daihatsu engine...

    but a 2 stroke with 3 rings:bowdown:

    the washers funny, ive had that happen once on a chainsaw... shame it smashed the coil mounts off...
    Last edited: Feb 24, 2011
  5. Dave C

    Dave C Member

    What cylinder are you going to run? The Chinese motor use a chrome plating that's very thin. That's why there's no replacement pistons for these motors. It's because there's no way to bore them to an oversize. Seeing how cheap a new jug and piston is for these things it's no wonder.
  6. HeadSmess

    HeadSmess Well-Known Member

    oh, im not planning on using them...came out of one of those tuk tuk things from thailand... just part of my collection of bits...

    twas strange, day after reading this, mate rings me...."my mower starters bust"

    yeah, ok, ill have a peek. oull starter off. fine. try turning engine... no go. turned backwards alright... all the way round, twice...4 stroke, new...

    hmm, check oil... and there you go!

    about an inch over "full", had to pull out about a litre of oil to get it right.

    oil had snuck in past the rings while it was sitting in the shed for 2 weeks... hydralic locked. only had to pull the plug really:p