help me diagnose raw motors problem? bad piston?

Discussion in 'Motorized Bicycle Trouble Shooting' started by johndzy, Nov 2, 2011.

  1. johndzy

    johndzy New Member

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    hey riders, I have A problem with my 66/80 cc raw motors engine, everything has been a nightmare. I bought the engine kit used in a box for 100$ and I have already put another 100$ into getting semi running on a bicycle. It wont run right at all... there is no power and when I have the engine engaged. When i pull the clutch the engine races. I have to keep trying to adjust the choke to even get it started, and I have to be pedaling atleast 15mph to get it started. Do i have a blown piston???... I have replace and adjusted the carb, the cdi the magneto... Im afraid of putting more money into it... dont know what to do? do you think it is forsure the piston... I mean what else could it be. please help me if you have had similar problems or understand the motor well. thanx happy trails :-||:-||
     
  2. Ibedayank

    Ibedayank New Member

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    what does the sparkplug look like?
    are you burning gas that has ethonol in it?
    Pictures are a great help
     
  3. maintenancenazi

    maintenancenazi New Member

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    Is your carburetor well sealed to the intake? It kind of sounds like a vacuum leak, that would be a good thing to check, if you haven't already. This is ONLY a guess however.
     
  4. rustycase

    rustycase Gutter Rider

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    IMO it would be best if you reviewed Alf's page of what to do with a new HT motor.

    ...and like the MN sez, ur biggest immediate problem is probably in the intake tract, especially if running a cns.

    disconnect your kill switch completely!
    could be intermittent problem with it.

    Good luck
    rc


    ...and don't be expecting gobs of power from a china girl! lol
    they get down the road, and up a few mild inclines, but that's abt it, on a good day! lol
     
  5. Goat Herder

    Goat Herder Gutter Rider

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    When a 2 stroke engine races at a very fast Idle that cannot be adjusted its usually a Vacuum leak. Check your carb manifold gaskets connection and that the carb is secure.
     
  6. johndzy

    johndzy New Member

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    wowow thanx guys, Why didnt i think of that, I looked at my intake and then my head gasket and 20% of my head gasket has melted away and is non existent, i can see through the gap inside my cylinder. Thats gotta be the problem... So next question is are the tollerances on the engine enough to put liquid gasket or should i buy a gasket..Imma buy one for now. thanx again
     
  7. Wm Holden

    Wm Holden New Member

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    you can make one out of a soda can...just buy one tho
     
  8. earl.k

    earl.k New Member

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    that would be your problem.. the only thing i can see going wrong with the piston is it locking up.. and then you motor would not turn over at all.. just get a new gasket, and make sure your head bolts are down good.. but not to tight. i just got done fixing my head bolt threads.. i over did it a tad and striped them out.lol i torqued them to 115 inch pounds this time... it seem to be holding up.

    gaskets are cheep. but if you dont have money to order it. i have a few that are usable. but your better off getting a new one.
     
  9. kolomootro

    kolomootro New Member

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    I wouldnt expect it to melt if you havnt run it alot.But you never know, I hope you fix it.
     
  10. Mozenrath

    Mozenrath New Member

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    Have you opened up your carburetor? My engine is a Raw motor, and the main jet in the carb was just sitting loose and quickly unscrewed comletely from vibration. So I screwed it back in and my engine has run great ever since.

    Since you had an air leak, I imagine that could create a lean condition which would make the engine hot enough to melt the head gasket, although I still find that highly implausible. The head gasket was probably just made poorly and couldn't stand up to the pressure.

    If you're really eager to get your bike running, it is possible to make one out of a soda can. While I don't have any pictures, you can read my blog where I made an entry on making a head gasket from soda can metal. Whether you make your own or buy a head gasket from somewhere like Sick Bike Parts, use a good gasket sealer. CRC Copper Coat is the one you want to use, from what I've heard from people. I've never had an air leak problem, but next time I replace the head gasket I'm going to use that stuff for good measure.
     
  11. rustycase

    rustycase Gutter Rider

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    I believe that any performance motor using and aluminum head on top of a cast iron cylinder should have the mating surfaces lapped, as Alf and other builders have described.
    IMO, a soda can is VERY thin aluminum stock, will most likely bring increased compression, and the pressures associated with that. Unless the mating surfaces are VERY good, the soda can probably won't work, regardless of sealer used.
    IMO, sealer is only valuable to prevent seep of liquid by-products of the combustion process. I don't expect the sealer to contribute to strength of the compression seal.
    I also feel it is important that a newly cast part be allowed to stabilize over a process of heating and cooling, in it's intended position of use. Especially when the fasteners are in the realm of 'marginal'.

    In the past, when dealing with troublesome 2 smoke engines that had head gasket problems, we cut a piece of annealed, thin copper wire, and made a ring of it to apply a bit of extra compression sealing, mechanically, to the gasket surface.
    It helps.

    Best
    rc
     
  12. Goat Herder

    Goat Herder Gutter Rider

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    Did you ever use Copper Coat Rusty? [​IMG]

    NAPA AUTO PARTS

    I have used this stuff with really good luck. I still have to adment that I have not done any exuberant gasket experiments. Yet this stuff is pretty amazing..
     
  13. BarelyAWake

    BarelyAWake New Member

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    BTW, a disposable aluminum pie tin (non perforated type ofc) is pretty good stuff for making replacement head gaskets, a little thinner than stock but thicker than a soda can ;)
     
  14. rustycase

    rustycase Gutter Rider

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    Yah, I used copperkote b4... goopy stuff w little shiny specs in it.

    just somebodies idea of a btr mousetrap... lol

    I'm kinda qualified... I earned a living for more than a few years as a mechanic on all sorts of engines, at different times. very big, to very small.

    I like the head gasket sealers for use around water ports thru the head/block, and where oil galleries pass through the castings.

    I really don't feel they have any value combatting the force of compression generated.]

    ...but that's my opinion... :)
    YMMV

    Best
    rc
     
  15. Goat Herder

    Goat Herder Gutter Rider

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    I got some shotty China's here that have never leaked. I believe the Copper Coat was first most t oughted as a fix to Cadillac's famous leaking head gaskets dilemma..

    Me gots a lot 0 wrenching experience.. A good 15 years always paying money to the passing tool trucks lol..
     
  16. Goat Herder

    Goat Herder Gutter Rider

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  17. rustycase

    rustycase Gutter Rider

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    ok... ok...

    try THIS one! lol
    SCE K&W Copper Coat Gasket Sealer - SummitRacing.com


    ... "a reliable sealing solution for any liquid-cooled engines when using SCE Pro Copper Head Gaskets".

    As I said earlier, it's just someone's scheme for a better mousetrap! lol

    ...on the liquid cooled engines I've used Victor and Fel-Pro head gaskets that are stamped on them NO Sealer.
    ...so maybe the sce gaskets aren't so good? lol

    Fun to banter about tech opinions, huh? lol

    I suppose the spray-on goopies aren't a bad thing.
    I know guys that swear by silver spray paint and nothing else.

    The one I use is Gasketcinch belt and gasket dressing.
    Just a very little bit of it at the galleries, and sometimes around the very perimeter of the gasket if I've got a seeper/leaker that I have not spent the money on for proper surfacing at the machine shop.

    ...but I would NOT do that on a performance engine...
    and that's what these tiny little engines are!
    ...trying to get a lot out of the smallest possible power plant! lol

    Fun stuff!
    rc
     
  18. Goat Herder

    Goat Herder Gutter Rider

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    I think a huge giving variable here that will perhaps be over looked by some one not familiar is the occasional casting defects on the sealing service area's. Where abouts the likes of a flat pane of glass and sand paper can correct.

    Quote While you're lapping the head you want to check the mating surface of the cylinder too. I use a piece of glass with 400 grit wet cloth paper to check the cylinder. Just make sure to clean the grit out before reassembly.
    Tom

    http://www.google.com/cse?cx=partne...#gsc.tab=0&gsc.q=Lapping the head &gsc.page=1
     
    #18 Goat Herder, Nov 8, 2011
    Last edited: Nov 8, 2011
  19. Mozenrath

    Mozenrath New Member

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    Yes, the surfaces need to be lapped. Using soda can aluminum should be considered experimental and risky. Air leaks should be tested for beforehand.
     

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