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  1. #1

    Join Date
    Mar 2013
    Long Island, NY

    Gap normal or not?

    Just picked up a Yamaha GP760 this passed winter. I have been trying to get it
    running right but have been experiencing a "lean runaway" condition.
    ie: When on the trailer the ski will warm up a bit then rev up to 8000 rpm. The
    only way to stop the runaway is to block the air intake, shut off the gas, or
    tap the throttle wide open. I have been planning on rebuilding the carbs to
    correct this issue after reading many threads on this site. Today when I was
    about to rebuild the carbs I noticed something that looked strange to me. In
    the area where the shaft connects to the engine there looks to be an open space
    that looks out of place. To me it seems like there should be some kind of seal in
    that area. I was wondering if this open space could be related to the lean
    runaway condition. I have attached some pictures to more accurately describe
    the space I am discussing. To be clear this image is of the part of the ski
    where the shaft connects to the engine (you are looking at the shaft exiting the engine). Is this space normal or is there a
    larger problem with the ski?
    Click image for larger version. 

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    After doing some more research it looks like my the crank shaft oil seal is bad. I did find pieces of rubber as well as springs, which I understand are part of the oil seal in my hull. What is the process for replacing crank oil seal?
    Last edited by ameraman697; 05-23-2013 at 09:25 PM.

  2. #2
    yea, it could be just the pic, but that looks like your rear seal sitting up against the coupler rather than inside the end of the crankcase where it belongs. I believe you have to pull the engine and split the case to put the seal in.

  3. #3

    Join Date
    Mar 2013
    Long Island, NY
    I think your diagnosis is accurate. I am going to pull apart the engine and change the front and rear crank seals. I would like to do this in the most simple way possible as this engine had a fresh top end rebuild 30hrs ago. Before i start this task i have several questions. 1) Can i split the case without removing the flywheel. 2) Are there any special tools I would need to complete this project. 3) As a result of taking the engine apart what other seals in other parts of the engine will defiantly need to be replaced. Can i just re-use all the other engine seals or do some always need to be replaced at the time the engine is reassembled. Should i get some type of rebuild kit with all the engine seals or can I simply change the 3 crank case seals then reassemble as that is my main problem. 4) How do the oil seals get reinstalled ie: what is the proper way to orient them in the case.

  4. #4
    You first want to understand why that seal is not where it belongs... .did the engine backfire into the crank and blow the seal out? If so, I'd also wonder that the reeds look like for that cylinder. There are varying camps on reusing seals... some say don't ever,others say the exhaust ones can be reused and if necessary, use copper gasket spray sealer on the. I'm still on the fence on that.... I have reused some OK, but if I got new ones without having to buy a whole set, I'd use new. I'll let others weigh in on their opinions.

    Special tools... you will need something to get the flywheel and coupler off. I used a puller on the flywheel and it came right off. I used a hardwood block of oak that just fit between the tabs on the couple, and smacked it with a small sledge... and it worked. There are also other suggestions in other thread on the coupler.

    As to the proper seal installation.... look at the stickies for engine rebuilds. The thing you really watch is the pins for the bearings..making sure those go back in the hole.

  5. #5

    Join Date
    Mar 2013
    Long Island, NY
    Re-assembling the engine today. Somone suggested applying sealent between the crank case seals and the crank case. Does it make sense to apply sealent in the area in addition to between both halves of the crank case.

    Also how do I realign the piston rings before I put the head back on. I hear if the piston rings are not properly aligned they could get caught on the exhaust port.

    Do i apply any lubricant to the new engine seals before i reinstall them?

  6. #6

    Join Date
    Aug 2006
    A little sealant can't hurt.
    Piston rings have to be aligned to the locator pins when you put the cyl on, not the head. IF not aligned you will not get the cyl down over the piston most likely.
    Yes, the seals have to be generously lubricated before install.

  7. #7

    Join Date
    Mar 2013
    Long Island, NY
    What do I lubricate them with?

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