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  1. #1
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    difference between reverse and standard rotation motors...HELP

    What is the difference between a standard rotation and reverse rotation motor. I have new rebuilt twin 350's and the starboard (reverse rotation) keeps blowing up. The port motor runs great and haven't had a problem in 9.2 hours. The first starboard blew up w/5.2 hours (crank bearing) and the next with 3.5 hours....just start hearing the crank KNOCK.....

    The builder says he will fix it again but it is costing me $ and time to r & r the motor.............

    they tell me that they are using marine gaskets, freeze plugs and different cam and a gear. Everything else is the same, does this sound right?

    What is the difference btwn the 2 motors? I only want to do this swap 1 more time.

    Thanks, Bob

  2. #2
    Registered KNOT-RIGHT's Avatar
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    Re: difference between reverse and standard rotation motors...HELP

    From my understanding there were two ways of counter
    rotation. Custom Ground cam or a gear drive two spin the Camshaft the original way.

    The distributer gear is ground different to keep the distributer and oil pump spinning the same way.
    The firing order on this custom grind is opposite of STD chevy. 12756348

    All reverse rotation engines have that firing order, and in saying that with a belt drive, timing chain, or three-gear(idler) the cam has to be ground specifically for that application so that the cam and crank both turn clockwise (as viewed from behind the engine). In this case the cam gear and distributor gear are ground to turn the distributor and oil pump in the standard direction.
    the two-gear timing setup used in stock Merc counter-rotating engines spins the cam in the standard rotation while the crank spins in the opposite direction, allowing a standard distributor gear to be used.

    So to Answer your question the differences would be
    Depending on what method used to counter.
    1) custom ground cam shaft
    2) Distributer gear
    3) three gear Idler (no Timing chain)
    4) Rear main Seal

    My guess is the Failure of your engine has nothing to do
    with the counter.
    Good Luck
    Gerry

  3. #3
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    Re: difference between reverse and standard rotation motors...HELP

    The oil holes in the crank are different. Talk with a machinist who knows his business I think the crank can be cross drilled

  4. #4
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    Re: difference between reverse and standard rotation motors...HELP

    I read this on another site:

    Two of the most inportant things on revesing and engine putting the pistons in 180 from normal. The wrist pins are slightly off center to make for the side loading at the top of the power stroke. The other thing is if you have the old style rear main seal you need one for reverse rotation.

    Never heard of such a thing b4. Is this right?

  5. #5
    Registered KNOT-RIGHT's Avatar
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    Re: difference between reverse and standard rotation motors...HELP

    I assembled my counter rotating blower engines last year.
    I installed custom Ross blower pistons. No note was taken to be installed 180. They are the same pistons from standard
    rotation to Counter. I cannot comment on that Idea.
    knock on wood mine are still together with 70 hours on them.
    I run Billet Sony bryant Cranks they are crossed drilled and are Identical in either motor. They are even Knife edged and the one in the counter is knifed on the wrong end.

    I even used the Same standard Rear main for both engines.


    However, Where the oil hole is placed on the journal
    of the crank should be in close proximity of where the piston
    actualy fires. This would in theory insure a film of oil in between. In a counter rotation the Oil hole is not at its proper clock position. This is what MMWalters suggests.



    Ask you builder what his clearences are?

  6. #6
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    Re: difference between reverse and standard rotation motors...HELP

    I am no expert but I do know for fact that mercs part number for a left hand (std)crankshaft and a right hand (counter) crankshaft are different. I also believe a good engine guy could grind the oil holes to work
    Last edited by mmwalters; 06-30-2005 at 05:15 PM.

  7. #7
    VIP Member VIP Member JaayTeee's Avatar
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    Re: difference between reverse and standard rotation motors...HELP

    Quote Originally Posted by foothill
    I read this on another site:

    Two of the most inportant things on revesing and engine putting the pistons in 180 from normal. The wrist pins are slightly off center to make for the side loading at the top of the power stroke. The other thing is if you have the old style rear main seal you need one for reverse rotation.

    Never heard of such a thing b4. Is this right?
    Yes it's right.

    On a R/H engine, the notches in the pistons
    face the rear.

    I've also heard that about the seal too.

  8. #8
    Registered Reed Jensen's Avatar
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    Re: difference between reverse and standard rotation motors...HELP

    Not all pistons have an offset wrist pin. The offset on the wrist pin is to compensate for piston slap. If the piston has an offset... make sure to reverse the direction of the pistons.

  9. #9
    Gold Member Gold Member Pwrbt33's Avatar
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    Talking Re: difference between reverse and standard rotation motors...HELP

    Pretty much everyone has covered all the bases. Your engine builder hopefully also knows that the crank has to be ground or polished in the reverse rotation as well. If not it will eat the bearings out of the motor. As covered, the seal, cam, firing order and dist. rotation are all already covered.

    Good luck.

    John
    Pwrbt33-John S.
    2012 World Champion Throttleman
    JAWS Marine


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