got the motor apart today!!
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got the motor apart today!!

  1. #1
    use a BBC to pull a BBC devanwon's Avatar
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    Exclamation got the motor apart today!!

    here are some pics of the internals, I only took pics of cylinder #1 pistons, and bearings. let me know what you guys think.





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  3. #2
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    Looks like not enough ring gap pushed the top of the piston off.
    Probably too mush compression for pump gas also.
    Need a lot more info to give you any kind of accurate answers.
    Bore, Stroke, deck hght, head cc, piston cc, Gasket thickness.
    (Pictures are real blurry)

  4. #3
    use a BBC to pull a BBC devanwon's Avatar
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    Quote Originally Posted by blownjet13 View Post
    Looks like not enough ring gap pushed the top of the piston off.
    Probably too mush compression for pump gas also.
    Need a lot more info to give you any kind of accurate answers.
    Bore, Stroke, deck hght, head cc, piston cc, Gasket thickness.
    (Pictures are real blurry)

    this is tuff being as I bought the boat with the motor together, the pistons are keith black hypurelectric (? I think thats spelled wrong, ) they are .060 over, rods say "GMB" and "153" on the end of the rod where it attaches to the crank. not sure on the stroke or deck height, also not sure on the head cc, I know that they are oval ports, here is the cam info link http://www.compcams.com/Cam_Specs/Ca...?csid=410&sb=2
    and the piston head volume -25.50, the bore says 4.310" on summits page here is the link for further info. http://store.summitracing.com/partde...8&autoview=sku

    let me know if you guys need any other info.

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  6. #4
    jetboataholic HawaiianJet's Avatar
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    Question

    What was it doing that made you pull it apart?
    HJ

    ***FOR SALE*** 1978 19' Full Stringer Hawaiian Molokai Jet Boat w/ Berkeley 12JC-AB and Chevy 440 Tall Deck ***FOR SALE***

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    Oh yeah, Forgot to mention that the hull is a special mixture of speedcote, herculiner and rain-x, all blended together- good for another 8 mph top end.

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    Quote Originally Posted by devanwon View Post
    this is tuff being as I bought the boat with the motor together, the pistons are keith black hypurelectric (? I think thats spelled wrong, ) they are .060 over, rods say "GMB" and "153" on the end of the rod where it attaches to the crank. not sure on the stroke or deck height, also not sure on the head cc, I know that they are oval ports, here is the cam info link http://www.compcams.com/Cam_Specs/Ca...?csid=410&sb=2
    and the piston head volume -25.50, the bore says 4.310" on summits page here is the link for further info. http://store.summitracing.com/partde...8&autoview=sku

    let me know if you guys need any other info.
    Still dont have enough info, but with that much dome volume on the piston you could be anywhere from 9.8 to11.0 Comp. which is too much for pump gas with a steel head. By the looks of things it was Detonating
    Probably happened during a hard pass.

  8. #6
    Senior Member CK7684's Avatar
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    Keith Black pistons require a bit more ring end gap than other pistons do, due to the way they expand...could be a reason...

  9. #7
    use a BBC to pull a BBC devanwon's Avatar
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    Quote Originally Posted by blownjet13 View Post
    Still dont have enough info, but with that much dome volume on the piston you could be anywhere from 9.8 to11.0 Comp. which is too much for pump gas with a steel head. By the looks of things it was Detonating
    Probably happened during a hard pass.
    So the guy I bought it from said it was 10.5:1, I was running a bit lean but if I get some new carbs will these pistons be good to run again??? I know that they are not forged but what should I go with???

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    Senior Member CK7684's Avatar
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    I'm running Keith Black pistons in mine...about 10:1 compression with alum heads...if youre running iron heads shoot for 9:1 or 9.5:1

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    im runnin somethin very close to this piston except the valve relief in piston dome.(mine all dome)10:5:1 and cam setup with open chamber Oval ports.Open chamber heads im runnin knock the compresion ratio back down to like 9:6:1 or so... depends what heads you have on your motor to figure the actual Comp ratio.

    Tom & Josh at Jetboat Performance had to clay my motor for clearance issues between the piston dome and the valves. was pretty close and had to go with a cam under 550 lift so I wont hit the valves at High RPM. You have a higher lift cam then mine but you also have that relief. So im not sure.

    Did you look at the valve for that cylnder and see if the valve is bent or if it had made contact with that piston? take it out and put in a drill and spin it to see if its wobblin?

    Id call Tom at Jetboat Performance and talk to him bro.
    Last edited by kcsteck; 09-02-2008 at 10:56 AM.

  12. #10
    use a BBC to pull a BBC devanwon's Avatar
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    the valve did not make contact with the piston, clearance is ok. just wondering on the piston ( forged vs. hypuerelutric)

  13. #11
    Sit N' Spin Jetaholic's Avatar
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    Quote Originally Posted by devanwon View Post
    the valve did not make contact with the piston, clearance is ok. just wondering on the piston ( forged vs. hypuerelutric)
    It's HYPEREUTECTIC



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  14. #12
    use a BBC to pull a BBC devanwon's Avatar
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    my bad , so should these be ok to put back in the motor or ???

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    Well people run the non forged no doubt.my buddy runnin non forged and so far Lucky! And you see what can happen when luck runs out..
    Forged is better for a boat motor that is gonna see High RPM most of the time.stronger more durable. If you got the cash get Forged.While your at it get Flat tops as well.

    Next time I build mine im goin flat tops instead of the 10:5:1 pop ups so I will have more choices as to how i want to build my motor instead of being limited from the Pop ups.


    my02 cents

    anyone correct me if Im wrong.

    k-dog

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    Hyper's are fine to put back in.
    Keith Black warns about popping the tops off these pistons if the rings are not gapped correctly:

    Special Notice on Top Ring End Gap

    The Keith Black pistons unique thermal conductivity, ring location and varied end use requires special attention be paid to top ring end gap. KB pistons make more HP by reflecting heat energy back into the combustion process and, as a result, the top ring runs hotter and requires additional end clearance. Increasing ring end gap does not affect performance or oil control because normal end gaps are realized at operating temperatures. Failure to provide sufficient top ring end gap will cause a portion of the top ring land to break as the ring ends butt and lock tight in the cylinder. The broken piece may cause further piston or engine damage. Safe top ring end gaps can be found by multiplying the bore diameter by the appropriate ring end gap factor from the clearance chart below.

    Example: 4" bore "Street Normally Aspirated" = 4" bore x .0065 = .026 top ring end gap. NOTE: Second ring end gaps do not need extra clearance. Dyno and track testing has shown that 34 degrees or less total ignition timing makes the best HP and time. Excessive spark advance, lean fuel mixture or too much compression for the fuel and cam used will make heat sufficient to butt piston rings with as much as .060" ring end gap. The entire top land can expand enough to contact the cylinder walls, when close to melt down temperatures are reached.

    The gap specs for a marine engine naturally aspirated are:
    Ring end gap factor= .0080"

    I run the same cam at 10:1 compression but with aluminum heads.
    Usually the big cams bleed off a bit of compression and allow use of 90 octane. I would use the best fuel you can get where you are located 92 or better.

    can we see some more pics of the other pistons and better shots of the broke one?
    Ring End Gap Facto

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