few crankcase questions

Discussion in '2-Stroke Engines' started by thuginfc, Sep 24, 2009.

  1. thuginfc

    thuginfc Member

    How do you split crankcase without damaging it?
    i noticed its pretty cheap metal

    How tight do motor mounts need to be?
    i used bout 10 ft/lbs but still seemed too much

    why do theese things snap bolts off in them so easily even grade 8?

    also how long should i expect to ride on of theese jet black motors for before having anymore serious problems?

    ive been through 2 of theese motors in th past month and want to get a good long ride on this thing when it cools off a little otside say 500 mile trip or so.

    anything i should know when reassembling this motor with new crankcase?

  2. thuginfc

    thuginfc Member

    also forgot to say theese arre jet black motors from zoombicycles if tht helps any
  3. linnix13

    linnix13 Banned

    how tight? tighten them till there tight, i tighten it manually by hand until its really tight but i dont reef on it,

    they snap bolts easily because of an improper alignment and vibrations and/or over revving it, i had grade 8 bolts in mine and they snapped because the load being placed on them was not strictly tensile, it has an axial load because i had the engine not perfectly straight, make sure its straight and lined up, also don't over rev and watch the vibrations,

    define a serious problem, my engine needs "maintenance" every night, and i have a serious break down only once every 3000kms, but you need to use loctite(blue) and lockwashers on everything, and make sure you check every bolt at night, keep the cables tight and keep the clutch tunes, oh and i blow a flat every hundred kms so bring a patch kit,

    a 500 mile trip is fine, i rode mine for around 500kms on a day trip once without a problem, but dont over rev, thats the key, and make sure your running the right mixture, i run 20:1 on mine, and with a 44t rear sprocket i dont exeed 40kph,
  4. Al.Fisherman

    Al.Fisherman Active Member

    I've looked at these issues, made some mods and haven't had any problems. First thing as far as studs go I buy grade 5 metric all thread rod. According to metric it is a 8.8 grade. Anything over a grade 5 is overkill and of no use...maybe worse. Torque specs on a grade 5 are way more then the cr*p material the Chinese use in making these engines. They won't stand up to that torque. I torque 6mm to 36 to 60 INCH pounds..that converts to 3 to 5 foot pounds, on 8mm I use a torque of 120 inch pounds to 180 inch pounds..10 foot pounds to 15 foot pounds. A torque wrench in inches should be used. All head, intake, exhaust, mounting studs get changed to grade 5 and get "RED" locktite. Should they need to be removed, the stock case will take over 700 deg F, enough to heat and remove the studs. On all my studs except the head get a grade 5 nut AND a additional grade 5 lock nut...also locked to each other. Now for the tension issue. I have had an issue with my engine rotating on the bicycle frame...not any more. Once I get the engine set up, and torque to the specs I use, I add a engine brace so the engine can't rotate on the frame. Thus the engine is secure in the static mode, good grade of bolts, proper torque and with the added brace...secure in running mode.

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