Cylinder head leaking...

Discussion in 'Instructions for Building and Repairing Motorized ' started by Lunatuck, Aug 11, 2019.

  1. Lunatuck

    Lunatuck New Member

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    I've very new to motorized bikes. I have a kit I was going to install, but a pre-built bike fell into my lap. It's been running intermittently. Sometimes good, sometimes bad. So I looked at the cylinder head and there was a slight leak. I tightened up the head a bit, but it doesn't seem to be sitting strait against the top of the cylinder. I'm afraid of over tightening. It also seems as if the head isn't sitting flush. maybe it's warmed. That said, the engine hasn't even been run for a single tank. Its still in break in.

    Not sure what I need to do, or exactly which make of engine this is. It's different then the one I have boxed up.
     
  2. Lunatuck

    Lunatuck New Member

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  3. Lunatuck

    Lunatuck New Member

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    Since I already tried tightening the bolts, I decided to pull the plug and remove the cylinder head. BUT as soon as I removed the first cap head nut on the side of the leak, I realized the whole bolt was coming with it. I'm thinking this means I have to take it all apart, but am afraid to see if its threaded. Does that sound right?
     
  4. ineededanamesoheresone.

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    I had this problem and it was the spark plug being loose. hand tightening it isn't good enough so throw a plug wrench on there and dont over tighten. It could also be the head gasket so remove the head and inspect the gasket for any dark spots with oil.
     
  5. curtisfox

    curtisfox Well-Known Member

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    Lay the head on a flat surface, table saw or the like. If warped get wet/dry sand paper, and get it flat again.........Curt
     
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  6. Greg58

    Greg58 Well-Known Member

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    If one stud comes out don't worry, take the other three off and remove the head. Clean the threads of the stud and add loctite to it and put it back in. Tighten the stud down by jamming two nuts together then let it set for a while before removing the nuts.
     
  7. Greg58

    Greg58 Well-Known Member

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    As Curtis said I sand every head to check for flatness, not all are true as they come.
     
  8. Lunatuck

    Lunatuck New Member

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    I was able to tighten this bolt down enough to prevent it from leaking. Torqued to 10 ft lbs.

    Its running much better, but I’m sure a disassembly is in order. Once I have the time to commit, I’ll do it.

    Theres still other stuff the bike needs first. The gear is rubbing the tire and the wheels are way out of true. Getting there, though. I was able to put about a mile on it today until I noticed the side of the tire was threadbare.
     
  9. Greg58

    Greg58 Well-Known Member

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    It's hard to tell by the picture which engine you have, the cylinder fins look rounded like a gt2b Grubee, if the head nuts are 10mm socket (6mm thread) it's a 48cc, if the nuts are 12mm (8mm threads) it's at least a 66cc engine.
     
  10. Greg58

    Greg58 Well-Known Member

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    If its got the rag joint sprocket mount the best way to true it is with the bike upside down on the seat and handle bars. I spin the wheel and watch for sprocket wobble and tighten the bolts in the area that needs it. Tighten the spokes on the right side of the hub in the area that is rubbing the chain, if the chain is rubbing all the way around either you need a thicker rag joint behind the sprocket or the wheel is out of line.
     
  11. Lunatuck

    Lunatuck New Member

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    Im going to try to true the wheels. I have an old excercise track stand thatll work, but first I need to install my hub/sprocket adapter when it shows up.
     
  12. Venice Motor Bikes

    Venice Motor Bikes Custom Builder / Dealer/Los Angeles

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    That gap you are seeing is perfectly normal!!! (in fact, when you over torqued it, i'm sure you warped the head & caused it to leak more)!!

    When you take the head off, you'll see a small ring on the head surface that actually seals to the gasket.

    Do as Curtisfox said & sand that ring on the head flat with some sand paper on some glass (or other flat surface)

    Re-install the head (with a new gasket) & torque it to 12 ft/lbs
     
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