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  1. #1
    Join Date
    Dec 2014
    Location
    Goldcoast
    Posts
    78

    Default Hot Cylinder on Two Stroke

    Hi all
    Trouble in paradise as they say.

    While bench testing my 1959 two stroke two cylinder 300 cc Goggo engine ( basically a motor bike engine ) I started getting one hot cylinder. other fairly cool. Significantly hotter only after a few minutes. Very hot after 5 minutes - like spitting hot.

    Ive gone thru all of the tests and possibilities and have come to the conclusion it is the little end bearing.

    Things Ive checked:

    a) Compression 110 psi on both cylinders
    b) Inspecrion thru ports and spark plug hole. All looks ok. Not the best way to check but I was looking for anything munched up in the cylinder.
    c) Fuel mix - 1:30 using victor two stroke mix and unleaded fuel
    d) Spark to plug good
    e) Engine sounds ok .. Slight rattle
    f) Engine running and sounds ok
    g) Turned the crank manually with and without plugs and insects. Again easy to crank nothing unusual.
    h) Spark plug NGK AB-7 .. On the cool side for a plug.

    I did notice the hot cylinder,s coil getting hot as well. Figure this is unrelated.

    Have I missed something ?

    Randal

  2. #2
    Join Date
    Aug 2008
    Location
    Adelaide
    Age
    68
    Posts
    1,373

    Default

    Any chance of posting pictures of the electrode end of the 2 plugs. Is it single carb or dual carb?
    Have you looked for leaks in the bottom end that might be causing that cylinder to be running lean?

  3. #3
    Join Date
    Dec 2007
    Location
    Sydney
    Posts
    395

    Default

    The rattle could be detonation caused by lean mix on that cylinder.
    How hard is it to take that cylinder head off to check the top of the piston.
    H.
    Jimcracks for the rich and/or wealthy. (aka GKB '88)

  4. #4
    Join Date
    Jul 2008
    Location
    near Warragul, Victoria
    Posts
    3,718

    Default

    Hi Randal. I'm no expert - but with 2 strokes, the crankcase seals have to be in good condition . With the 2 stroke system, the crankcase is pressurised to some degree , you can test the crankcase for leaks . I have a few vintage chainsaws and they usually need new seals fitted Mike

  5. #5
    Join Date
    Dec 2014
    Location
    Goldcoast
    Posts
    78

    Default

    Hi all
    Thanks for the info. I'm back home next Tues. Out in the Wild West visiting family. I'll have a closer look and send thru pics ..

    Randal

  6. #6
    Join Date
    Jul 2012
    Location
    Malvern East
    Posts
    84

    Default

    Check for Exhaust leaks at the Cylinder to pipe Joint no two stroke likes leaks at this critical point

  7. #7
    Join Date
    Dec 2014
    Location
    Goldcoast
    Posts
    78

    Default

    I'm back sure must say the weather was picture perfect out west.

    ok spark plugs. New plugs. This is after about 20 minutes running.
    Attached Images Attached Images

  8. #8
    Join Date
    Aug 2008
    Location
    Adelaide
    Age
    68
    Posts
    1,373

    Default

    Which plug was in which cylinder?

  9. #9
    Join Date
    Jul 2008
    Location
    near Warragul, Victoria
    Posts
    3,718

    Default lean

    The lighter coloured one has been running lean , hence overheating . The lean mixture causes a longer burn , which makes more heat .

  10. #10
    Join Date
    Dec 2014
    Location
    Goldcoast
    Posts
    78

    Default Head and Pistons

    Pics of head and Pistons below. .. checked clearances etc .. Nothing obvious, all look ok

    pic 1 - underside of head cylinder 2 - hot one
    pic 2 - cylinder 1,- cool one
    pic 3 - Pistons - LH cylinder 2 hot one,
    - RH cylinder 1 cold one,

    current theory is leaking crank case seal
    Attached Images Attached Images

  11. #11
    Join Date
    Jun 2005
    Location
    Helensburgh
    Posts
    618

    Default

    Quote Originally Posted by Goggomobile View Post
    Pics of head and Pistons below. .. checked clearances etc .. Nothing obvious, all look ok

    pic 1 - underside of head cylinder 2 - hot one
    pic 2 - cylinder 1,- cool one
    pic 3 - Pistons - LH cylinder 2 hot one,
    - RH cylinder 1 cold one,

    current theory is leaking crank case seal
    Do a leak down test before going any further, guessing has blown up more two strokes that I care to think about.

    https://www.youtube.com/results?sear...der+two+stroke
    CHRIS

  12. #12
    Join Date
    Dec 2014
    Location
    Goldcoast
    Posts
    78

    Default

    Yep ... Did a test ... Leaking like a sieve .... Cylinder to cylinder and through the seal into the dyno. Lucky it didn't fry the dyno.

    Explains the different plug colors and deposits on cylinders and cylinder temps

    I started pulling it down today .. Will keep me off the streets for awhile.

    Many thanks to all for your help. I give an update as I go.

    ������������������.

  13. #13
    Join Date
    Jun 2005
    Location
    Helensburgh
    Posts
    618

    Default

    Even after you re-build this motor or any two stroke a leak down test is the first thing to do as confirmation. The job isn't done until it is confirmed leak free.
    CHRIS

  14. #14
    Join Date
    Apr 2002
    Location
    Brisbane
    Posts
    429

    Default

    Just as an aside and nothing to do with the original problem ...... you would be wise to go to a better quality two stroke oil ..... one that is capable of running at 50:1, even if you continue to run at 30:1.

    The modern high perfromance two stroke oils lubricate way better and run way cleaner than the old type rubbish they put in mowers.

    cheers
    Any thing with sharp teeth eats meat.
    Most powertools have sharp teeth.
    People are made of meat.
    Abrasives can be just as dangerous as a blade.....and 10 times more painfull.

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