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  1. #41

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    I guess you may be replying to me here. If you can't turn it with the strap wrench, the piston is hitting something, and there is an internal problem. You should feel a hard stop in this case. Compression feels like more and more resistance as it turns. Since it is a 2 stroke this resistance is on every revolution, where a 4 stroke is one upward stroke compression, one downward stoke power, one upward stroke exhaust (exhaust valve open - no compression), One downward stroke intake fuel, and it all repeats again. You probably know this if you are willing to work on a motor. I was hoping you would have inserted the spark plug turn by turn until you feel the problem you are experiencing.

    Does the spark plug you were inserting show the positive and negative side of the electrode smashed together?

  2. #42
    Quote Originally Posted by AL_Mark View Post
    I guess you may be replying to me here. If you can't turn it with the strap wrench, the piston is hitting something, and there is an internal problem. You should feel a hard stop in this case. Compression feels like more and more resistance as it turns. Since it is a 2 stroke this resistance is on every revolution, where a 4 stroke is one upward stroke compression, one downward stoke power, one upward stroke exhaust (exhaust valve open - no compression), One downward stroke intake fuel, and it all repeats again. You probably know this if you are willing to work on a motor. I was hoping you would have inserted the spark plug turn by turn until you feel the problem you are experiencing.

    Does the spark plug you were inserting show the positive and negative side of the electrode smashed together?
    Yes I was replying to you, Mark, you in Alabama? I'm in Gardendale, just north of BHM.

    I can replicate the situation so I will try the backing out of the plug sometime today.

    The plug electrodes are fine., not smashed together


  3. #43

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    i am in SE HSV. I am constantly messing with motors as a side hobby. My latest project is a Jonski powered by a 500 yamaha. I am of polish descent and thought the ski at the end was fitting. Got another post I brought back to life of me testing an aftermarket carb rebuild kit and the problem with the aftermarket diaphragms that I think is interesting.

  4. #44
    Myself's Avatar
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    Stop wasting your time. There is a bad low end bearing. Either lower rod, or a cage came apart on a main. Pull the engine and split the cases already.....


  5. #45

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    That is what I am thinking "myself". HAHA I crack myself up sometimes!!! Another pun. But is it worth putting money into this old 787? Probably going to need a new crank.

  6. #46
    Quote Originally Posted by AL_Mark View Post
    i am in SE HSV. I am constantly messing with motors as a side hobby. My latest project is a Jonski powered by a 500 yamaha. I am of polish descent and thought the ski at the end was fitting. Got another post I brought back to life of me testing an aftermarket carb rebuild kit and the problem with the aftermarket diaphragms that I think is interesting.
    So you must hang out at Smith Lake then. We have a place by Big Bridge.

  7. #47
    Quote Originally Posted by Myself View Post
    Stop wasting your time. There is a bad low end bearing. Either lower rod, or a cage came apart on a main. Pull the engine and split the cases already.....
    Yeah, I was kind of waiting for someone to sum it up that way. Not what I wanted to hear, but at least I can focus on my other XP now. Eventually I'll get this pulled and report back.

  8. #48
    Myself's Avatar
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    The 787 is AWESOME......and damn near bulletproof......totally worth rebuilding. On a side note, I just finished one up and fired it off today! Taking it apart will just cost you some time. The flywheel and PTO can be removed in a big vise with a bit of heat after the crank is out. If you're lucky it might just be a front main bearing which can be replaced pretty easily. I do not like SBT cranks, I use WSM for most hard parts.

  9. #49
    Quote Originally Posted by Myself View Post
    The 787 is AWESOME......and damn near bulletproof......totally worth rebuilding. On a side note, I just finished one up and fired it off today! Taking it apart will just cost you some time. The flywheel and PTO can be removed in a big vise with a bit of heat after the crank is out. If you're lucky it might just be a front main bearing which can be replaced pretty easily. I do not like SBT cranks, I use WSM for most hard parts.
    I love the 96 XP which is why I've had at least one since 96. Unfortunately I can't always keep one of them running so I'll be picking up a Spark Trixx next weekend. I still plan on getting one of my XPs up and running in time for summer.

  10. #50

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    Hey Myself. The NADA says this motor puts out 110hp. That's damn good for 782CCs for back in the 90s. How did they get that HP out of it? RPMs? Do you think it they were honest on this HP? You seem to view them as reliable. To get this HP, Yamaha had to go to 1051 CCs, and they had to triple carb it to get more air into it.
    Last edited by AL_Mark; 02-27-2021 at 08:27 AM. Reason: more information

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