Cooper head gasket

Discussion in '2-Stroke Engines' started by FelipeCobu, Aug 8, 2011.

  1. FelipeCobu

    FelipeCobu Member


    This weekend after some running I found an oil leak from the head gasket also find the head nuts way loose.

    Ok following the instructions posted here I will replace the studs and nuts, the nuts I will use OEM VW Beetle head nuts this are steel made.

    Examining what I found under the head I see that are to much piston deck, I didn't measure the compression ratio Yet. But o would like some advises about some ideas I had:

    1) My engine is still at break in, I was thinking about change the stock metallic gasket for a thinner copper gasket to increase the CR a little.

    2) I found a sharp corner around the place where the gasket seats I know it is no good cause may lead the engine to knocking and also disturb the flow in the combustion chamber, should i file this sharp corner a little?

    Excuse me in case of error English is not my native language!

    Felipe Cobu

    Attached Files:

  2. Al.Fisherman

    Al.Fisherman Active Member

    I mill the head/cylinder right out of the box. Never a problem, and I use the stock gasket with copper Kote.

    Language...better then yours to me.
  3. FelipeCobu

    FelipeCobu Member


    Yesterday I deburred the sharp edges of the combustion chamber.

    Also confirmed the poor finishing of the sealing surfaces so, following the tips here - over again, I milled it using sand paper against a true flat surface.

    I molded the interior of head using "epoxy putty" so now I can study the squish gap angles and ,if needed, I will cast and machine my own head in the future.

    Then I decided to take out the cyl. assembly and discovered my engine block soaked on gasoline (almost 100cc inside), although I didn't saw any leaking from the carburetor.

    Concluded that it could be an petcock failure, an I right?

    Today I will go for the new gasket and descent studs.

    Felipe Cobu
  4. Al.Fisherman

    Al.Fisherman Active Member

    Either that or you forgot to close petcock. Reason for leak in engine is that the float isn't closing the needle all the way (seating into the seat). This can be caused by incorrect float adjustment, trash between the needle and seat, or defective needle and or seat. I don't have leaks (3 builds at home) into my engine, weather I close the petcock or not. But we do close them for safety reasons.
  5. FelipeCobu

    FelipeCobu Member

    The leaking problem is not new. The last time I coped it was the float arm pin that slided off, It tried to solve it with one drop of CA glue each side. Then I probably have two (needle and petcock) problems. Will test the seating of the needle.


    Felipe Cobu
  6. FelipeCobu

    FelipeCobu Member

    This weekend i measured the compression ratio of my 70cc engine (thought it was 66cc but it is 47x40 = 70cc), found that the advertised (9.0:1) CR is wrong this number if for an engine without the gasket, put the gasket on and the CR will drop to 7.5. Changed to copper gasket - 0.2mm height - and my new CR is now 8.9. Will test and see what changed on performance soon.
  7. FelipeCobu

    FelipeCobu Member

    I'had made a test run last Saturday results:

    Final speed was 43 km/h now it is 49.5 km/h.

    The bike uses 26" rims and 2.125 Kenda Flame tires.
    Using 44x10 pinion sprocket ratio.
    Rider weights nearly 230 pound.
    Using the original muffler, the next goal is to build a tuned pipe.

    Some little porting and more CR really changes power!

    Felipe Cobu
  8. geebt48cc

    geebt48cc Member

    Uno, after 200 miles, I milled head + took head gasket off, sealing the head with only Siellacn . Use 12lbs torque on head. It's not like the same engine, seams like it comes somewhere other than CHINA? For size, holds its own!

    Double torque up hills..............

    Remember, go synthetic at this point. 32:1
    Last edited: Aug 22, 2011
  9. FelipeCobu

    FelipeCobu Member

    Attached some images of my current modifications and improvements, I didn't take a pic of the bike completed yet.
  10. FelipeCobu

    FelipeCobu Member

    Image 1: Measuring the volume of the chamber in the head.
    Image 2/5/7/9: Fixture for installing a moped sprocket (that uses 415H chain) to a dic brake bicycle hub.
    Image 3: Using BW beetle head nuts im my engine (grade 12 steel).
    Image 4: Better quality gaskets and cooper gasket for the head
    Image 7: Deburred the casting marks.