is it true that 2 stroke motors have ....

Discussion in 'Outboard Maintenance' started by T1mb3rW0lf, Jan 13, 2010.

  1. T1mb3rW0lf

    T1mb3rW0lf I Love microskiff.com!

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    lower compression per cylinder then a 4stroke would so if I were to do a compression test it wouldnt have as high of lbs per cylinder ???
     
  2. B.Lee

    B.Lee Well-Known Member

    Not neccessarily, it depends greatly on the engines in question.
     

  3. Frank_Sebastian

    Frank_Sebastian Well-Known Member

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    No, there is more to it than that. For years GM made a two stroke diesel engine that was used in many city buses. The compression was about 22:1 or twice what a car engine would be. You could smell it almost before you saw it coming.

    The fellows that post on this forum are very "with it" when finding out things using internet search engines. Ask the question and give the year and make of your engine. No doubt you will get the information you need.

    Best regards,
    Frank_S
     
  4. Brett

    Brett > PRO STAFF <

    Diesel 4 strokes run compression from 275 to 400 psi.
    Gas 4 stroke stock automotive about 150 from what I remember,
    I don't ever remember measuring over 130 on any of my 2 stroke outboards.
     
  5. DuckNut

    DuckNut Brandon, FL

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    I had an older Merc 2 stroke that ran like a raped ape for years with only 65lbs compression.

    For Brett- some newer diesel technology are pushing 550 and above. Have a '06 Jetta TDI with 617-623 in all cylinders.
     
  6. Brett

    Brett > PRO STAFF <

    Forgive me DN... I was operating from memory.
    I haven't worked on a diesel in 20 years.
    I can only plead ignorance of the new technology.

    ;D
     
  7. T1mb3rW0lf

    T1mb3rW0lf I Love microskiff.com!

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    yeah this motor is an 04 yammie 2stroke f40 3 cyl and they are all reading in the 100's - the number just seems low to me as I am used to hearing 125 -145. I figured I would put it out here and see what you guys have to say on the subject. I guess I was a bit vague.. Sorry I am a bit of a noob when it comes to mechanical things
     
  8. Brett

    Brett > PRO STAFF <

    I can live with compression readings over 100 psi on a used 2 stroke.
    As long as all cylinders are reading the same plus or minus a few psi.
    A hot engine will give different readings than the same engine cold.
    Also a "wet" compression test will give a different read than a "dry" test.
     
  9. T1mb3rW0lf

    T1mb3rW0lf I Love microskiff.com!

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    yeah this was on a very cold motor this morning I didnt have it running for any amount of time today at all and basically was just sitting there when we did it this morning around 9:30 am after a nice lil frost here in New Port Richey..
     
  10. TomFL

    TomFL Well-Known Member

    I second everyone's notion on the importance being more on the evenness than the actual #'s.

    I've seen the same motor yield compression #'s even but at ~ 8lbs test difference between 2 different PSI gauges.

    -T