engine/jet question
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engine/jet question

  1. #1
    classic hot boater Orange Peel's Avatar
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    Default engine/jet question

    I have a BBC I ran in a bahner I have, for some reason the thrust bearing in the crank was destroyed along with the crank. I had the crank fixed and had some other block work but nothing came back bad on line bore and had plenty inplay clearance. Put motor back together and put it in a different boat and got same results? Can my pump cause this?

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    Senior Member TNYoungblood's Avatar
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    Yes. If the bearing is shot it can cause all kinds of problems with your bottom end. Spin your pump by hand and see how it feels
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    classic hot boater Orange Peel's Avatar
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    The pump in both boats are literally brand new builds. The gullwing is the last boat I tried and I had another motor in it for longer run time and it didn't hurt the crank? Wasn't as much power and rpms.

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    Senior Member jetboatperformance's Avatar
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    To expound on what Mike said , excess movement (for/aft) in your drive front bearing or pump shaft can wipe out the crank thrust, imagine that the impeller wants to drive the pumpshaft forward thru the bow of the boat , also sticky or rusty splines (drive line and pump shaft) or lack of (or inadequate) space between your driveline female spline and pump shaft bearing snap ring etc Double check/examine your pump shaft splines for twist or distortion too ... lots to look at

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    mo balls than $cents$ IMPATIENT 1's Avatar
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    Is it destroying the thrust sides or journal side the worst?

    Dare to be different, if it turns out great you can claim you planned it that way.

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  8. #6
    classic hot boater Orange Peel's Avatar
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    But what's the odds of both new pumps are causing this? I understand what u r saying but all looks to be ok. Also if I run one motor and have no problems then run this one a month later shouldn't I get the same results from the pump? I think it is in the crank or block?

  9. #7
    Some guy obnoxious001's Avatar
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    Quote Originally Posted by Orange Peel View Post
    I have a BBC I ran in a bahner I have, for some reason the thrust bearing in the crank was destroyed along with the crank. I had the crank fixed and had some other block work but nothing came back bad on line bore and had plenty inplay clearance. Put motor back together and put it in a different boat and got same results? Can my pump cause this?
    Exactly how much is "plenty of end play clearance"? Did someone, either you or the shop, measure the block and rear main cap?

  10. #8
    Senior Member jetboatperformance's Avatar
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    Quote Originally Posted by Orange Peel View Post
    But what's the odds of both new pumps are causing this? I understand what u r saying but all looks to be ok. Also if I run one motor and have no problems then run this one a month later shouldn't I get the same results from the pump? I think it is in the crank or block?
    What we term "pinning the thrust" is often caused by the lack of clearance between driveline female spline and pump thrust bearing (can be as simple as how the motor is mounted ) , example ... In a auto or truck situation if in a manual trans one had a foot against the clutch constantly the crank would continually ride against the thrust control main bearing and wear out the crank and or the bearing

  11. #9
    classic hot boater Orange Peel's Avatar
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    Well on the crank the side of the thrust plate closest to the jet I'm gona say the back.. is worse, real black. The side closest to the balancer is worn but not black. The part of the bearing that the thrust rides against is almost gone.

  12. #10
    classic hot boater Orange Peel's Avatar
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    I had the engine put together, said there was 5 thous inplay clearance.
    I ran another engine in the same boat and mounts with now problems.
    I was just thinking this happened twice to this engine so must be a problem in block? I really don't want to pay for this again if the machine shop is at fault. But you know it will not be his fault according to him...

  13. #11
    "Sweet Summer Time" Mrs.HolyDiver's Avatar
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    Nate.....this is P... How much play is in the yoke when you slip it onto the 'splines' ? Boat to Boat this will change, no 2 the same... Pumps are always trying to pull themselves through the hull... its what they do !!! HA Exactly what JBP is saying...
    Last edited by Mrs.HolyDiver; 10-09-2014 at 04:58 PM.
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  14. #12
    Senior Member eliminator's Avatar
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    Nate, I think you need to check that the driveline is not jammed into the pto . should have some clearance front to back . I have seen this before.
    Spider Monkey Racing
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    Senior Member DuaneHTP's Avatar
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    This may not be relevant, but something to consider. On these engine swaps, did you use the same PTO, Driveline AND same Flywheel on all engines? Reason I ask, is I've seen different thicknesses of flywheels cause this same problem.

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    Senior Member 74Bonneville's Avatar
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    If you slide the driveline in all the way until it stops, then back it out, exactly how much clearance should there be?

    I'm about to move the engine forward in my Daytona and want to get it right.

    I seem to recall reading 1/16" to 1/8"


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