657 vs. 657x engine comparison
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  1. #1
    PWCToday.com Is My Home Away From Home Myself's Avatar
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    657 vs. 657x engine comparison

    I've see the questions come up about these engines every now and then. A while back I rebuilt one of each and noted the differences as I went along. These differences are from my personal observations only. If you have more information please feel free to add it. The 657 engine is rated at 70hp while the 657x is rated at 80hp. There are several reasons for that which you will see shortly.


    Let's start by looking at the exhaust pipe. Here is the style pipe that was on the standard 657 engine.


    And here's the one from the 657x engine.

    It has a slightly larger expansion chamber which would help produce more power.


    Next the carbs, The standard 657 runs a pair of BN-38 carbs arranged like this.


    The 657x runs a pair of BN-38I carbs in a little different setup.


    They are both 38mm but I assume the I series must be a little better design.

    The intake manifold itself seems to be identical in both versions.

    The 657x runs a little more agressive rotary valve than the standard version. I can't remember the specs but I'm sure somebody can enlighten us.

  2. #2
    PWCToday.com Is My Home Away From Home Myself's Avatar
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    Re: 657 vs. 657x engine comparison

    The cranks will interchange between both versions but the originals are different. Here is the crank from the standard 657 engine.


    And here is the one from the 657x engine. It had full circle type counterweights. My only guess on this would be less vibration at higher rpms???


    The PTO and flywheels on each were identical.

    The crankcases themselves have a number of differences between them for starters, how about case drain plugs?? I can't imagine why one version has them and one doesn't. Maybe the drilling and tapping leaves a weak spot with potential to crack out? Or maybe corporate decided it would save a buck? Who knows.



    Here are the case drain locations from inside.



    Now how about this feature, I believe this was a design change to help strengthen the case as a whole.


  3. #3
    PWCToday.com Is My Home Away From Home Grumpy Old Guy's Avatar
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    Re: 657 vs. 657x engine comparison

    You got your cranks backwards,the one with holes is from a std 650.

  4. #4
    PWCToday.com Is My Home Away From Home Myself's Avatar
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    Re: 657 vs. 657x engine comparison

    Next, the backside of the cases. I don't even know what this little boss would be for.



    Looking down from the top, look how this area is more defined and enlarged in the X case.



    Looking at the intake side there are 2 MAJOR differences. For starters the pulse lines to the carbs hook up on opposite sides. This is due to the change in carbs. More noteworthy are the very much larger intake ports on the X engine. Again, a trait of more power.



    Here is what the intake ports look like from the inside. Look at how the X case is carved out nicely to promote better air flow. There appears to be enough meat in this area to carve it out in the standard case.


    The cylinders between the 657 and 657X are NOT the same. Just eyeballing them you can't see a difference.


  5. #5
    PWCToday.com Is My Home Away From Home Grumpy Old Guy's Avatar
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    Re: 657 vs. 657x engine comparison

    The boss on the back of the case is the starter support bolt hole.

  6. #6
    PWCToday.com Is My Home Away From Home Myself's Avatar
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    Re: 657 vs. 657x engine comparison

    Even the port mapping and sizes are the same. But if you mix-match them you will run into some problems. The X cylinders are 1mm shorter than the regular 657 cylinders.



    This helps raise the piston just slightly out of the bore at TDC.



    Now, you CAN use either cylinders on either engine as long as they are of the same type. You can also use 1 standard 657 cylinder on your 657x if you mill 1mm (.039") from the bottom of the cylinder. I know it will work, I have done it. The exhaust on the 657 cylinder will then also be lined up with the 657x cylinder.



    From the top the heads look identical.

    Last edited by Myself; 01-27-2010 at 09:39 PM.

  7. #7
    PWCToday.com Is My Home Away From Home Myself's Avatar
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    Re: 657 vs. 657x engine comparison

    But on the combustion side they are different. The X head has a smaller volume. Combine this with the shorter cylinder and you get a much improved performance boost in the compression department.


    You can install a 657X head on your 657 if you'd like a small bump in compression.

    The stators and electrical boxes were also the same on these.

    And of course the 2 of them assembled.



    Again this information is from my own observances. Feel free to do with it what you wish. Also please add any information you might have.

  8. #8
    PWCToday.com Is My Home Away From Home Myself's Avatar
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    Re: 657 vs. 657x engine comparison

    Water Worx, thanks for the info! It has been 2 years since I did that project. I was going through pics on the computer and realized I never made this post like I was going to. So many projects, so little time.

  9. #9
    PWCToday.com Is My Home Away From Home seadoobutch787's Avatar
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    Re: 657 vs. 657x engine comparison

    The 657x was the first seadoo i rode. It was a 95spx, At the time i thought it was real fast lol, now i have a limited 96xp which is way faster.
    Last edited by seadoobutch787; 01-28-2010 at 11:31 AM.
    1997 Seadoo SPX---limited mod
    1996 Seadoo GSX--Cruiser
    1995 Kawasaki 550/750sx---Conversion ski
    http://www.pwctoday.com/showthread.p...750+conversion
    https://www.youtube.com/watch?v=ucxd...TcG7qp45xTX9xV

  10. #10
    Frequent Poster bsdbum's Avatar
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    Re: 657 vs. 657x engine comparison

    Im liking that green =) I bet it looks killer with the purple pipe and green / white hull(s).
    My Current Fleet:
    95 Seadoo XP 800 - The Couch
    90 SN SJ - 701 61x piped fun boat
    98 RN SJ - 701 61x/62t (under the knife)

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