Spark plug too long? I have a cheap fix.

Discussion in 'Whizzer Motorized Bicycles' started by RdKryton, Jan 24, 2009.

  1. RdKryton

    RdKryton Active Member

    Hello all.
    I have read a few posts about the concerns of the C7E plug being too long and extending into the combustion chamber by a couple threads. I have a simple solution that only cost me 80 cents. I have read that a few people have removed some of the head to allow use of a shorter plug but I took a different approach. I bought a copper gasket that is the correct thickness to make the plug fit perfectly in the head. The two threads that were visible are now in the head where they should be. Heat transfer should not be a problem because the gasket is copper. The copper gasket is for a high pressure banjo fitting. Napa part #26982 $0.80 each. This may be a coincidence but my Whizzer even started a little easier even though the temperature was only 33 degrees F. Still too cold for me to ride.
    I have enclosed a picture. Hope this helps.

    Jim
     

    Attached Files:


  2. Quenton Guenther

    Quenton Guenther Motored Bikes Sponsor

    Hi Jim,

    I have used the copper washers to "index" the plug, but if more than 2 are used it will effect the heat exchange between the head and the spark plug. Using the copper washer is far better than leaving the nose of the plug exposed in the combustion chamber, but the best solution is have the plug match the depth of the spark plug hole.

    Another important side effect of using the washers is reducing the chance of damaging the threads when the plug is removed.

    I totally agree with you and recommend using washer, but if possible have head modified to match the plug thread depth as the best solution.

    Have fun,
     
  3. RdKryton

    RdKryton Active Member

    Hi Quenton
    I am only using one washer. It is about 2mm thick and is just the right thickness to keep the thread from being exposed in the combustion chamber. I bought a couple extras so I can give one to Kilroy and have a spare.

    Jim
     
    Last edited: Jan 24, 2009
  4. Quenton Guenther

    Quenton Guenther Motored Bikes Sponsor

    Hi Jim,

    2 MM is a thick washer in fact that is approx. .078". I was using much thinner washers .055". One thicker washer should be better than several thinner ones. Do you have a way to check head temperature? I will check with one of the local NAPA stores to get a few to test. When I installed 3 single washers [.165"] the head temperature increased about 5 degrees over no washers. When the head was cut down to use the C7HSA plug the head temperature dropped 22 degrees. I will check it with 1 thicker washer [.078"] and then 2 thicker washers [.156"] and let everyone know the results. Most of the heads were .165" short of threads for the C7E spark plug.
    A trick to remember is to try to get the spark plug to "index", I usually buy them by the box, and try each one to find the better ones.

    Have fun,
     
  5. go-rebels

    go-rebels Member

    Hi Quenton,

    Do you check head temps using a thermocouple or IR sensor?
     
  6. Quenton Guenther

    Quenton Guenther Motored Bikes Sponsor

    Hi Go,

    I used to attach a sensor on one of the fins near the spark plug, however the meter stopped working, so now I use a hand held IR unit. I don't know how accurate it is because I only use it for comparison. Of all the items I have tested the following reduce operating temperatures:

    Painting the cylinder with black cylinder paint, installing a high fin head, copper head gasket, matching the spark plug length in the head, carburetor jetting, exhaust modifications, and changing the ignition timing are at the top of the list. When time allows, I will also test a few items with special coatings, thanks Ray V. for supplying the parts to test.

    Here are a few items that didn’t change the temperature, painting the head, painting the cylinder silver, changing the spark plug heat range [using different plugs], milling the head [.060”], and replacing the 10 MM head bolts with 8 MM versions, and advancing the camshaft.

    Have fun,
     
  7. go-rebels

    go-rebels Member

    Hi Quenton,

    I wonder how accurate the IR method is when changing coatings. You're really measuring the temperature at the surface of the paint, rather than the surface of the metal underneath. And you have variables that cannot be easily controlled when you measure the temp at the surface of different coatings: emmisivity values (of the coating), coating thickness, and coating thermal conductivity.

    But if you're changing other variables (plugs, timing, etc.), then the comparisons are 100% valid regardless of the coating!
     
  8. Quenton Guenther

    Quenton Guenther Motored Bikes Sponsor

    Hi Go,

    When I tested the different coatings I was using the attached sensor equipment. I was smart enough to remove a small portion of the coating [paint] where I attached the sensor in order to get a more accurate reading. I knew the coating would insolate the readings and in fact "hold" the heat in. When I tested the cylinder paint I used the head temperature as a guide to changes. 99% of all tests used the head as the reference point.

    Hope this information is helpful.
    Have fun,
     
  9. Quenton Guenther

    Quenton Guenther Motored Bikes Sponsor

    Results are in.......

    19 degrees cooler [head temp] by using spacers to flush the spark plug tip with the combustion chamber. Main advantage is keeping the threads out of the chamber and allowing plug removal without removing the threads in the head.

    Reducing the spark plug ramp to match the actual spark plug length lowers the head tempature more [22 to 28 degrees], but is far more costly to do.

    So there ya have it, a cheap fix for a problem that should have never happened in the first place.

    These comments are not entended to "bash" any company, person, persons, employee, employees, vender, or vendors.

    Have fun,
     
    Last edited: Feb 20, 2009
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