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  1. #1

    Thrust Point in 1.8L SC Motor???

    I'll try to keep this short...

    I've got a SHO motor that we thought cold seized.... But after pulling all 4 pistons out of it, the crank was still extremely hard to turn. So after further investigation, we found that the crank would move front to back about 1/4". The counterweights of the crank actually ate up the aluminum block.

    Can someone explain to me what is in that motor that keeps the crank from "thrusting" or moving front to bank in the journals?

    Wish I had pics, but the motor is down the shore and I'm in the city till the end of the week.


  2. #2
    abracadabra's Avatar
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    I ran into the same problem when my pump blew out and pushed the crank forward. There is no thrust bearings on these motors, way to go Yamaha!!! You will have to take your block to a machine shop to have trust bearings build and machined into the block, Julio...

  3. #3
    suck my wake's Avatar
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    Quote Originally Posted by treemoney View Post
    I'll try to keep this short...

    I've got a SHO motor that we thought cold seized.... But after pulling all 4 pistons out of it, the crank was still extremely hard to turn. So after further investigation, we found that the crank would move front to back about 1/4". The counterweights of the crank actually ate up the aluminum block.

    Can someone explain to me what is in that motor that keeps the crank from "thrusting" or moving front to bank in the journals?

    Wish I had pics, but the motor is down the shore and I'm in the city till the end of the week.
    The crank is held in place by the by the washer behind the drive coulper, there is no spec or tolerance for thrust on these motors. The manuals calls for you to replace this washer with a new one every time you remove the coupler. Once you torque that coupler on the crank won't move back and forth.

  4. #4
    Quote Originally Posted by suck my wake View Post
    The crank is held in place by the by the washer behind the drive coulper, there is no spec or tolerance for thrust on these motors. The manuals calls for you to replace this washer with a new one every time you remove the coupler. Once you torque that coupler on the crank won't move back and forth.
    Wrong, the crank is positioned-centered in the block by the thrust bearing surfaces which are integral in the block. Many motors have side insert thrust bearings, like Mitsu, but the SHO block uses the block itself, with two small oil grooves cut into the thrust bearing surfaces on the block, for added lubrication. No need for a beefy thrust surface, the crank is normally un-loadad on thrust so its no big deal, untill you have a pump fail and shove forward on the crank and hurt the block. Already done it myself..
    Crank end play spec on any engine of this displacement would be from .005-.010 thou.

  5. #5
    suck my wake's Avatar
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    Quote Originally Posted by rossnemo View Post
    Wrong, the crank is positioned-centered in the block by the thrust bearing surfaces which are integral in the block. Many motors have side insert thrust bearings, like Mitsu, but the SHO block uses the block itself, with two small oil grooves cut into the thrust bearing surfaces on the block, for added lubrication. No need for a beefy thrust surface, the crank is normally un-loadad on thrust so its no big deal, untill you have a pump fail and shove forward on the crank and hurt the block. Already done it myself..
    Crank end play spec on any engine of this displacement would be from .005-.010 thou.
    AH yes, I stand corrected. I just went down and looked and yes the center web of the upper part of the block has a small thrust surface with the two grooves machined into it. Last night when I checked this I was only looking at the lower part of the block and it has nothing on it for a thrust surface so when looking at the manual and seeing no thrust spec's the only thing I could see is that the washer between the drive coupler and bearing kept the crank from moving, well at least moving inward. I learned something new today, thanks Ross

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