to tear down or not

Discussion in 'Motorized Bicycle General Discussion' started by Donbia, Mar 11, 2012.

  1. Donbia

    Donbia New Member

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    I had asked in one thread how meany have torn down there motor right out of the box to check it out before installing it, also how meany have just installed it out of the box with just a good look over first, and if so what issues have they had in doing so.

    I did not get a answer form that post, maybe this time, or is it just dumb to ask?

    Seems to me taken out the spark plug and putting the piston top below the exhaust port and blowing air though the spark plug would blow out any junk in the cylinder, or at least let you see if any is there. Also a mirror could be used as well.

    I haven't received my kit yet, but people keep saying to replace the studs and re tap the stud holes, If the studs are not all the way down, then there should be one or two up further then the rest I would think. I just hate to have to almost rebuild the engine when it is new, but caution is good too.
    That why I am asking this.

    I am not saying not to do a tear down, but a carefully look over might prevail as well. :-||
     
  2. BarelyAWake

    BarelyAWake New Member

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    While some suggest a complete teardown & replacing everything, all the fasteners and even including bearings... I personally think this a touch overkill, particularly for such a low cost engine.

    Do what you wish ofc, to each their own - but I find a compromise between that and what you've suggested to be "good enough" for these kits. I pull the cylinder, which is a mere four nuts (& perhaps a base gasket, they tear sometimes even on a new motor) - yet allows a visual inspection of all key areas (inc the amount of flash in the ports/removing if necessary), decking/lapping all cylinder gasket surfaces & cleaning the lower end of any potential debris, the only fasteners I feel must be replaced are the mount studs & nuts (too soft) & the acorn nuts used on the head studs (as they can bottom out before full head torque). The side covers you'll be pulling anyway during the build/install (clutch mag & sprocket) and I see no need to replace those fasteners as there's no load on them...

    Part of the charm of such a simple two stroke is this light "top end rebuild" is quick & easy and other than a coupla fasteners won't cost you anything but a few moments of your time, yet still ensures there's no garbage in the motor and that everything's put together correctly (& w/loctite) - even if the head studs are properly seated as you'll see any discrepancy in depth (threads remaining) and length.

    As for splitting the case and replacing bearings? Well... ya can if ya want to but given the generally low quality of the rest of the engine I really can't see the point aside from the amusement factor. You could replace every one yet it still won't fix the sloppy casting misalignment, out of balance flywheel & crank, sloppy wristpin & other assorted personality quirks these things are known for... you can ofc attend to those as well, but at some point you'll hafta ask yourself if it's worth the effort - or should you seek a higher quality engine? If you enjoy rebuilding for the sake of tinkering, well... that's a different story lol

    Honestly? They're toys. Wonderfully fun toys but at some point disposable, no matter what you do. I've one that's got over 10,000 miles on it (all stock parts) and the cylinder's chrome liner (below ring travel) is disappearing. I could replace the piston, rings & cylinder... but why would I bother as for the effort and just a little more money I could get another that hasn't the bottom end wear? I've another engine that ate a cage at 4000 miles & instead of cracking the cases I just bought an $80 replacement motor & kept the old for parts...

    Your call ;)
     
    #2 BarelyAWake, Mar 11, 2012
    Last edited: Mar 11, 2012
  3. 2door

    2door Moderator
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    I concure and add that tearing the engine apart before installation is not bad advice but, the builder must recognize that a certain amount of mechanical experience will make that step a little less of a potential disaster. One must determine if disassembly of an engine and more importantly, correct re-assembly is within their mechanical ability. If curiosity is a factor and you just need-to-know what's inside and have confidence that you can get it back together right, then go for it.
    I feel that the majority of successful motorized bike builds out there are ones that were installed out-of-the-box, with stock fasteners and care during the installation. The performance/longevity seekers will always strive to get the most from these little 2 stroke wonders but if the project is more of a novelty and just something to play with, and you have no experience with small engines and no desire to learn about what goes on inside, install it and enjoy it. The odds are in your favor that everything will work as designed.
    Tom
     
  4. Donbia

    Donbia New Member

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    Thanks for the reply, I think I will just remove the spark plug if it,s put in and bring the piston to bottom dead center so the exhaust port is open, shine a light in and use a mirror to see inside, if it looks OK then blow some air though to make sure.
    bring the piston to top center and look in the bottom if possible, if OK, then re-torque the cylinder head and put the engine on the bike.
    Maybe new cylinder head nuts and waffle washers that I have seen on meany small motors to keep head nuts tight, just have to look and see what they are.

    I think caution is good, but to over do it is unnecessary with a new motor, unless you are setting it up for racing and such.
    I do have the knowledge and skill to it, over 25 years as a mechanic and 5 years as a machinist.
    But as above I am not interested in rebuilding a new motor.

    Thanks to all that responded to my thread. usflg
     
  5. Al.Fisherman

    Al.Fisherman New Member

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    My first engine out of 6 was installed right out of the box. Never again. Although I may go beyond what others feel needs to be done, I want to know that everything is good to go, weather it be 1 mile to the store or a 20 mile round trip to any one of three adjacent towns. After the first engine was installed (cylinder studs not torqued down, blew a head gasket), I have never had trouble with the remaining 5. Here is what I now do to all my engines, pick what you like, discard the rest, but keep it handy.

    https://docs.google.com/document/d/1GcesQihc7-mm3hJGf7UPiqOaRXZ8ekUT99QUZq2qXXE/edit

    Should you have starting problems, take a look at this:
    https://docs.google.com/document/d/1omvHOrPyn5zvv-2sx-GNyWPjmryEeLt7zYVQup22ppE/edit

    The MOST important thing to remember...install the engine correctly..make sure the mounts are as flush with the tubes as you can. The optimum "V" angle is 75 degrees.

    I've worked on all kinds of engines in the past 50 years, these are the simplest to work on bar none.
     
    #5 Al.Fisherman, Mar 11, 2012
    Last edited: Mar 11, 2012
  6. robbomberbomyea

    robbomberbomyea New Member

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    i have run mine right out of the box,no problems at all,other then idle needed adjusted,chain adjustment,clutch arm adjustment just the basics,nothing internal.now maybe ive been lucky,dono, only two builds.one from bgf other from pirate cycles.third build still in box,grubee starfire,nos.gt-3. though it wouldnt hurt to do visual inspection of motor,clutch,magneto, clean fuel tank etc.
     
  7. Allen_Wrench

    Allen_Wrench Resident Mad Scientist

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    I bought my own engine from That'sDax years ago. At that time, I'd read that he had a good reputation for customer service in many people's opinion. So I did not feel a complete tear-down was absolutely necessary.
    But I did check for lubrication in the clutch actuation, checked head bolts and case bolts and carburettor assembly. It all seemed to have either been gone-over before or assembled with some care. This same engine survived a wreck that the original bike it was on did not. It is now mounted in my current bike and running fine, so I am resisting the temptation to muck about with it too much.
     

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