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  1. #1

    Yamaha SUV 65U Middle Cylender down! Pictures and looking for advice!!

    I have been posting in the performance 2 stroke forum & have been told that this might be a better place to post as much of the performance forum guys are GP guys, & that the old schoolers may be able to offer better advice.

    I live in Hawaii & have had this SUV for for about 6 years. I don't use it a lot but love it for filming & diving from. I have been good about servicing the ski & when it needed repairs I have had a local guy do it. the first mod I did was to by pass the oil pump & go to premix. I recently put in a new pump & stator in it, & use only Non Ethanol Fuel in it. The last time I used it it ran Fine & then I parked it for about a year. Unfortunately I was not schooled in the fact that if I was going to let it sit for some time to run it & turn the Fuel knob to the off position & let it run till the gas ran out! So the ski sat idle for about a year before I bought a new Battery & wanted to put her in the water. I sprayed some starter fluid into the Carb box & it started right up! I put it in the water & ran it for about 15 min & then it seemed to bog when giving it gas... So bad that I knew something went wrong. I did a compression check & the numbers didn't lie Cylinder 1. 120 psi. Cylinder 2. 30 psi. Cylinder 3. 120 psi. I pulled the head off & the attached photos are what I found. Some have said that this looks like a Crankshaft rod bearing going bad. I am eager to hear everyone here's input. From the other Forum the majority were saying that I should pull the whole engine split the halves and check the crank. I am curious what your opinions are & would like to know what I should be looking for If I pull the whole crank out... will it be obvious? Do I need to pull it all out.. I also have a lot of questions as far as what will need to come off the engine to get it out, & what can be left together so that I don't waste more time than necessary.

    What I am thinking is that maybe the ski sat with fuel in the carbs for the year & pluged a jet. The ski ran for 15 min lean in the mid cylinder & therefore the middle cylinder crankshaft bearing did not get enough lubrication & went out.. what do you guys think?

    I am torn between doing a costly rebuild & just going full on and doing a 4 stroke conversion to her.

    any thoughts?
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  2. #2
    quadzilla's Avatar
    Join Date
    Apr 2007
    LOCH NESS Monster-Land


    Hey there..

    Firstly, unfortunately you have a bit of a mess on your hands here.
    - BUT. Fixable for sure.!

    Pretty surprised to see you have any compression at all in #2 let alone 30psi.

    As for running lean for fifteen minutes.? that amount of damage can happen in 1-3 seconds.! (at 7000rpm that's 116 power strokes per second.!!)

    Yes, It's going to be fairly obvious whether a small or big end bearing has went out when the cylinders come off.!
    - At this point I'd suggest you pull the motor out the hull before going any further.
    - Working on it, In that monster of a hull is a PITA to say the least..

    Not sure what the availability of a doner four stroke is going to be like on the Hawaiian Islands.??
    - either the FX140 or FX160 would be a very good choice of conversion in that hull. (the vx1100 would struggle I reckon you'd hate it)
    - Obviously the 1800 motors would be a nice choice if available or one of the seadoo motors.

    Your next step is get the motor out or at a minimum get the cylinders pulled off and see what went wrong..

    Again this is very much fixable..!!

  3. #3
    what are the costs Im looking at if? What would I need to purchase to fix this motor? I am not a big fan of the SBT options but how will repairing it myselfe compare price wise?

  4. #4
    quadzilla's Avatar
    Join Date
    Apr 2007
    LOCH NESS Monster-Land

    Post ?

    Hey again..

    Impossible to tell at the moment what it will cost to repair.!!

    More importantly have you ever rebuilt an engine 2 stroke or otherwise.??
    - In the last Six years you have owned it have the carbs been rebuilt.??
    --(you really should be on to your 3rd-4th carb overhaul. most people me included don't go thru our carbs often enough.!)

    Regardless this motor HAS to come out..!!
    Once it's out and the cylinder is off then a plan of action could be put in motion.

    Realistically the crank needs to be removed and inspected.!
    -Some of the little jagged pieces of piston crown and squish band on the head are almost certainly down in the crankshaft area. (Via the transfer ports..!!)
    If you look at your second image at about a couple of minutes to twelve position you can see what looks like something embedded in the piston crown.?
    --(possibly a piece of a bearing.?)

    What condition is the cylinder liner in.? is it damaged.?

    If this was my engine..

    1/. Engine out and on the bench. (Quick visual inspection of the cases for breakout damage.)

    2/. break the motor down completely.! (Making sure to get the flywheel and rear coupler off while the motor is complete.!)

    3/. Inspect crank.! If it seems ok.? then pressure wash the shit out of it. followed by a thorough dry with an air line.
    - then into the parts washer followed by a coating of 2 stroke oil, then into a bag and put aside for later.
    -- If the crank is FUBER'd then obviously step 2 gets skipped.! then it's a New or used crank as you options.

    4/. Inspect the cylinder and remaining good pistons. (if they're good consider a light hone and new rings)

    5/. Inspect the reeds. (decent chance of damage or metal contamination here. left unchecked, they "will fuck up" the engine again)

    6/. By now the decision to proceed or throw in the towel with this motor will have been made.

    7/. If we're proceeding then it's time to get in about the carbs..
    - I reckon this is where the fault (KILLER) is likely to be found.??
    -- either,. a choked up internal filter.? A split fuel pump diaphragm.?? warped or damaged fuel body check valves. or a shit load of corrosion..

    8/. Time to start sourcing the parts required for reassembly.
    - New OEM crank seals. Carb rebuild kits (Mikuni only) New OEM Gaskets as required. Used or new piston (Assuming the liner doesn't need rebored)
    -- The cylinder head could do with being replaced. Used would be totally fine.!!

    9/. Order (if not in hand) Sealants and loctite products as required (threebond 1211 is as good as it gets for sealing the case halves)

    10/. GET it rebuild..!!

  5. #5
    Aloha Quadzilla,

    Thanks for the quick reply's. you know your stuff! I am going to take your advice! It sounds sound. I have recently been told by the local mechanic here in Hawaii to first pull the cylinders off & see if Im " Lucky " By crank bearing being the upper crank bearing (which Im assuming he means the top rod Bearing ). & sense I don't have a huge space I was thinking about doing this first rather than pull the whole engine out.

    If I were to be lucky & it being the top rod bearing I take it your advice would be to still take the engine out to clean & inspect the rest of the crank, Clean it etc..

    So if I am going to pull the motor, what do I need to do or take off to get the motor out?

    Step by step guidelines would be greatly appreciated!

    I hate to be a pain. I do have the yamaha service manual, but its not realy descriptive, & I would like to take off the big chunks of pieces together rather than taking every little piece off.

    Again thank you in advance for sharing with me your wisdom!


  6. #6

    Join Date
    Sep 2013
    Bennettsville, SC
    I lost the mag side piston on my raider 760 a couple of weeks ago and mine looked way worse than that. Pieces of ring embedded in the piston and head. Crank was fine though, so keep your fingers may get lucky. I did the entire cylinder exchange with SBT, and I was very satisfied, both with the parts, and the machine work. Everything fit together perfectly. Blew my motor on a Friday, back in the water breaking her back in the next Thursday. Going to take her to Charleston this weekend and do some riding around the Cooper river.

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