Checking compression: Kick start vs. Electric
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Checking compression: Kick start vs. Electric

This is a discussion on Checking compression: Kick start vs. Electric within the Technical forums, part of the Caferacer.net Forums category; I've searched the forum and can't find anything. This past weekend I checked the compression on my '75 CB360. Since my bike is partially disassembled ...

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  1. #1
    Junior Member shidifen's Avatar
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    Checking compression: Kick start vs. Electric

    I've searched the forum and can't find anything.
    This past weekend I checked the compression on my '75 CB360. Since my bike is partially disassembled I didn't have the battery. So to check the compression I just kicked the bike over 4-5 times. I got 100psi from both cylinders.
    I was talking to some buddies at work about the compression because I'm not sure if 100psi is good or not. They felt that if I had used the electric start I would have seen a higher compression reading.
    Does this make sense? I would have thought that the compression would be the same regardless how fast the motor was turning over. Provided you have a good seal between the piston and the cylinder aren't you just compressing air (air fuel mixture) independent of speed?

    Many thanks,
    Stephen
    shidifen
    1975 Honda CB360T

  2. #2
    Senior Member JackC's Avatar
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    Be sure that the chokes are open on both carbs, and that the throttle is held wide open when you kick it over. Kick it until the reading goes no higher.


  3. #3
    Senior Member roccitycafe's Avatar
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    make sure you take the spark plugs out too, it might give a more accurate reading if you just take the carbs off, as the vacuum slide may not be rising at all on kick start, 100psi is pretty low for that bike though, but make sure you're not causing resistance somewhere before tearing the thing apart

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  5. #4
    Senior Member craig641's Avatar
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    Take the spark plugs out to check compression? I'd assume you screw the compression tester into the sparkplug hole. What effect would removing the other sparkplug have on compression? But what camshaft do you have on this bike? Is this static or dynamic or effective compression?

    Craig

  6. #5
    Senior Member Geeto67's Avatar
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    why are you checking the compression cold? Air cooled motors have loose tolerances and really you should be checking this with the engine up to operating temp. Checking cold really all you want to see is that there is not a huge difference between the two.
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  7. #6
    Senior Member HackAsaw's Avatar
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    Do ya reckon air cooled engines have more ring gap per inch of bore than water cooled engines?

    Accidental inventor of the worlds fastest wearing rocker arms and other edible engine parts! Try my yummy blue cheese camshafts!

  8. #7
    Senior Member kenessex's Avatar
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    quote:Originally posted by HackAsaw

    Do ya reckon air cooled engines have more ring gap per inch of bore than water cooled engines?

    Yes


    Ken
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  9. #8
    Senior Member HackAsaw's Avatar
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    How much is that?

    Skirt clearance.... plenty of air cooled engines run a half thou.

    I think a new hd runs a thou and a half on the skirts, right out of the box.

    Stem to guide... same.
    Accidental inventor of the worlds fastest wearing rocker arms and other edible engine parts! Try my yummy blue cheese camshafts!

  10. #9
    Senior Member HackAsaw's Avatar
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    Btw.. kick or electric should give the same valid numbers
    Accidental inventor of the worlds fastest wearing rocker arms and other edible engine parts! Try my yummy blue cheese camshafts!

  11. #10
    Senior Member kenessex's Avatar
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    quote:Originally posted by HackAsaw

    How much is that?

    Skirt clearance.... plenty of air cooled engines run a half thou.

    I think a new hd runs a thou and a half on the skirts, right out of the box.

    Stem to guide... same.
    How much is that?

    I would say 6 +/- 2

    Skirt clearance.... plenty of air cooled engines run a half thou.

    Plenty cold seize where the studs distort the bore and plenty run more.

    I think a new hd runs a thou and a half on the skirts, right out of the box.

    I think Briggs and Stratton runs 3.5 on the skirts, right out of the box.

    Stem to guide... same

    Not on a Briggs.

    Ken
    P.S. I might have made my numbers up.
    WERA 119
    CCS 119
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    \"Think twice before you speak, and then you may be able to say something more insulting than if you spoke right out at once.\"
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