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  1. #11

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    Just a quick reminder about the history of ski. Someone installed a complete new SBT in here. Other issues that were not addressed caused motor to bite the dust. There is a sticky at top of page on PWCToday titled" Another SBT blew up" Why it made sticky status, is beyond me, but I GOT A STICKY!!!! I am published!

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    This is engine exactly as it came from previous owner that had nothing to do with the idiots that originally installed it. He dumped some oil in crankcase on rod and crank bearings. First thing that was done right so far.

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    I dont usually deal with salted skis, so do not know the amount of time it takes for paint to flake away like this. The ski has been sitting up for a few years. I guess salt never stops working its destruction. For this engine a slow death by salt intrusion. I guess if sat long enough it could turn into a pile of salted remains that would still resemble a crankcase. That is until it was disturbed. Then would be just another pile of a salt byproduct.

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    I like what I see here. The crank assembly looks like new, rolls smooth and no sounds, except for the counter shaft gears. Lower thrust washers are a nice clean dull silver. The upper rod bearing surface is flawless. May be fortunate to just assemble a new top end and ready to drop back in ski, but....

    Instinct tells me no. So lets split the case and make sure nothing else may be an issue here. If all is good I will go ahead and install new outer crank seals. Very cheap insurance at this time.

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    Since this surface corrosion is not going to fix itself, I decided to bead blast while case is split apart. Then repaint and basically building a new motor at this point. If crank assembly looks good after thorough inspection when removed, it will go back in as is. So far, I am optimistic about it from what I see. But that doesnt mean anything until its apart and check everything over very closely.

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    Looking closer at the left intake tract, its obvious there has been minor welding performed in usual place when lower end lets go or skirt breaks and falls down. Nicely done and a perfect fix. Wish I could find more dead motors with only minor damage like this one to repair. SBT does opt to take cores that are not badly damaged. I guess if they didnt, decent used cases would bring a premium and not get credit for a salvageable core.
    Last edited by Seadoo timebomb; 09-25-2012 at 09:03 PM.


  2. #12

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    Instinct usually does not let me down. Soon as I removed stator cover bolts, it just falls off. Everything inside here is clean as a whistle, but the locating pins or dowels are not anywhere to be found. I am guessing when new motor arrived they just boxed their core and on its merry way out the door the box went. Then when assembling the motor realized that it may have been a good idea to remove old ones from core before it left. Or not. Just one possible scenario. Dont like mine? Then make up your own.

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    Now its time to split the crankcase and see if it was the right thing to do. I dont have the first hand history of what happened to this motor for why it took a dump. Only what I found to be wrong after a quick visual.

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    Here is a flywheel puller I made form some aluminum round stock. Just a copy of the Seadoo or aftermarket puller. Common design to many small engine makes. It just screws on to the threaded hub of flywheel and large bolt screws down pushing against the end of crankshaft.

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    Even tho the puller is made out of aluminum, I have used it dozens of times and not any signs of threads pulling or stripping out. I did machine threads to be a very tight fit on flywheel, just for this concern. So far so good. Continuing on...
    Last edited by Seadoo timebomb; 10-11-2012 at 01:49 PM.

  3. #13

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    Next thing is remove the plastic retainer holding starter bendix in place, then pull it out. Make sure you keep up with the load spring in retainer. Its necessary and not easy to find if accidentally dropped on floor. Not to mention the bounce factor times ten places it can get lost.

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    If you hold the front and back of bendix then rotate it will spread apart slightly. Looking closely you will see three tangs spaced equally apart inside dividing the spring loaded weights. These small pieces will break off and then short out your stator windings. So if you are blowing a fuse on your mpem, this is one place to consider a problem.

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    Last edited by Seadoo timebomb; 10-11-2012 at 01:50 PM.

  4. #14

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    Flip the engine around to the pto. Remove large bolt that secures pto flywheel on. With a standard harmonic balance puller you can remove the pto flywheel easily enough. Unless someone previously used a large impact to tighten, this should pop off with relative ease.

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    With crankcase sitting upside down, you can see where the paint has been coming off from salt water. All it takes is one little scratch for salt water to dry on bare aluminum and its there for the duration. It will start eroding away at the surface and work its magic under the paint. Then blisters up and flakes off. Lather rinse repeat, until you have an ugly corroded mess.

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    The small space between where pto seats and rear crank seal has salt buildup. It flakes off easily enough, but still the threat is there. Time will cause the steel crank to develop rust and pitting, so bad the machine ground sealing surface will not be salvagable.

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    After removing all of the bolts, I had one heck of a time trying to split these case halves. Definitely used plenty of silicone here on this block to seal everything. Finally got it to pop apart and then able to separate the two case halves. Now to look everything over and see what condition its in.

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    After pulling the crankshaft out of the case half, I immediately noticed lots of salty residue from water ingestion building up between crank bearings in case. Things are not looking good so far.

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    Last edited by Seadoo timebomb; 09-25-2012 at 11:41 PM.

  5. #15

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    Well this is just what I didnt want to see. The crank bearings are all rusted up. Good thing I went ahead and split the cases apart. It would have really sucked if I just did a top end and put this ski back together. If you are doing just a top end on a ski that the history is not known, be aware this is a possibility you may experience.

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    All three bearings on the side that piston had taken a dump are rusted. Even a large buildup of crusty salt up against the inner seal. This side of motor took a lot of water in and its likely the owner didnt bother to remove it in any timely manner.

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    OK this crank is a great candidate for a core to get a rebuilt. If I had proceeded with my first intent of doing a topend only would have been a costly mistake. BUT even had I taken it down this far and found nothing wrong, it was worth the trouble just to confirm there isnt an issue after ski is back together. Wouldnt it totally suck to be out on a long cruise then motor takes a dump and no one around to tow you back the 14 miles from where you launched? Can you say a bad day?
    Last edited by Seadoo timebomb; 09-26-2012 at 03:35 AM.

  6. #16

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    Well its time to get something going back together now instead of just making a scrap pile. You need to do a thorough cleaning to crankcase prior to assembly. This is a different case than was disassembled before. I had this sitting around and was in great condition. Thought it was about time to get some use. The other I will bead blast clean and remove all of the salt burns before it gets put to use.

    If you notice all of the machined bearing pockets are very clean and shiny. Well except for one. The arrow is pointing to bearing pocket for counterweight shaft is oversize. The bearing has been spinning instead of captured. It will keep getting worse if not addressed and eventually cause some serious damage if bearing fails. Usually will not be repairable if occurs. There are not many options to repair this easily. The only one I have used is just filling with JB Weld and then bolt case halves together.

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    It doesnt take much to do the job, just a little dab to spread on each case half.

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    You see the thin coat applied to pocket. Do it on both halves. If you choose this way to repair dont spread it all the way to gasket surface. Leave a little gap there so when compressed it wont push up to the machined sealing area. There is no danger of doing a repair this way. The bearing is sealed, in a dry cavity that is also sealed away from any lubricants. The case will still come apart just as easily the next time there are repairs done.

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    Even tho the JB Weld has decent working time you need to have everything prefit before hand and ready to assemble. When dropping the crank in, you have the small pins on bearings that fit in their respective pockets. Rotate accordingly then crank will drop down all the way. Outer seals need to have a layer grease applied between inner lips. I dont like using any type of sealant of the seals. Just a very light wipe down of some thin grease to help not pinch when cases are set together. The seals have a 360 degree compressed contact surface of rubber and no reason to leak. You will have to install outer seals onto the crank journal before setting down in case. Center the crank so the two steel retaining washers will spin freely or both are tight, all depending on the clearances. You can tap the crank on either end to achieve this. With the blunt end of screwdriver handle tap on each bearing to make sure they are seated in pocket. This will make for easier placement of other case half. Drop counterbalance shaft in and index with marks on gears. The center bearing on shaft must seat in pocket. Slide it one way or the other to fit. Next push the two seals away from bearings so they seat against the shoulder in case. Make sure they are square and straight. Rotate crank over to make sure everything spins freely.

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    Last edited by Seadoo timebomb; 09-27-2012 at 11:41 AM.

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  8. #17

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    I am constantly wiping off the sealing surface on case halves with a rag dipped in lacquer thinner. I want a very clean oil free surface for sealant to adhere to. One last wipe then apply a very thin layer of Threebond, Yamabond, Hondabond, Goldbond, if you have the itch, or Loctite 518 as per the Seadoo manual. A very small uniform layer is all that is needed. Doesnt have to cover every bit of the sealing surface. If you just draw a line in center of sealing surface and circle each bolt hole with sealant will work fine. When compressed it will get pushed out both sides and 100% covered. Set the other case half on and work down all the way till the two make contact. Drop all of the bolts in and run them all down by hand, not power tools. I normally just apply some molybdenum disulfide, which is the black automotive wheel bearing grease to threads and flange of head on bolts. If you are doing serious salt water riding, may consider thread sealer under head of bolts.

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    Torque down in 5 pound increments following the sequence from Seadoo manual. Torque all of them up to 20 foot pounds. Then torque the larger bolts again in 5 pound increments to 30 foot pounds. I would recommend using a clicker torque wrench. Do not get in a hurry when torquing at all. Slowly pull the torque wrench until it clicks. If not sure correct value is reached stop and apply pressure again. At 5 and 10 pounds the bolts will not be tight enough to get a real feel for the click. At 15 pounds it should be noticable. When doing the final torque of smaller bolts, some may not feel like they will ever click. You should get the feel of how much each need to be turned to reach the next torque value. When in doubt, stop and then apply torque again. Dont keep pulling on wrench if you are unsure. Just stop and apply again. Do this if necessary until wrench clicks. Some of the smaller bolts that get torqued to 20 ft-lbs may feel like they are going to strip out, but once all of the gasket sealer is completely compressed, they will reach correct settings. I have noticed this on every case assembled and just quit worrying about it. Now its done. Time to take a break and find a cold beverage....
    Last edited by Seadoo timebomb; 10-11-2012 at 01:57 PM.

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  10. #18

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    Since the motor in ski was originally a rebuilt from SBT, it was bored out to 1mm oversize. They do this simply for eliminating unnecessary setups for boring cylinders. All of them get punched out the same size and usually yields a 100% cleanup. Makes final assembly time kept to a minimum too. SBT does not charge against your cores if liners are no good. If jug is not damaged, you dont get hit for bad liners if yours are dead or too big to bore out any larger. My plans are to take this motor to largest bore size readily available without having to alter anything else. Aftermarket sizes are common up to 1.5mm. Larger ones are available, like from Wiseco, but I dont care for them in any of my skis. They require much more piston clearance to run, and thats not acceptable in my book for this application. If setting up a motor for racing purposes, then might fit the application better.

    It wont do much good to go into detail in boring out cylinders, since very few would have access to the proper equipment to do the work. But I will cover a light overview of the process. Even tho It aint rocket science, without basic machine shop practice would be a nightmare for anyone to do for themselves. Here is the cylinder set up on a fixture I built to bore the 951's. There are many different types of specifically designed boring systems that all will give precision results. The boring bar I have is a Van Norman that was built back during WW II, and still precision as any newer equipment. Most modern machinery has been designed more for specific use to keep time and labor cost to a minimum. Thats the least of my concern. I just want the ability to be able and bore/hone to finish myself. I wont rely on someone elses supposed expertise. Way too many screw ups from dumbphuks out there pretending to be machinists. If I specify a certain size or clearance, and they go oversize, its my problem. If they fail to meet the minimum clearance and dont bother to tell me or cant read a micrometer or bore gauge, the motor is toast and its my problem. Not to mention they charge way too much for the quality of work offered. Here are a few pics of boring bar passing thru sleeve and removing material to specified size.

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    Now the cylinder is bored to specified dimension just undersized enough for a finish hone to achieve a proper crosshatch.
    Last edited by Seadoo timebomb; 10-11-2012 at 02:04 PM.

  11. #19

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    It took some years following others to figure out their mistakes. Then I went my own separate way. Most people I have dealt with would bore undersized a very safe amount, then hone up to the finish size. This could be much as the clearance for piston itself. My plans are to have a finished honed cylinder with 0.0055" clearance. I had people in the past that would bore up to just the piston size and then hone the difference to finish size. Thats a lot to remove for a hone. With an interrupted cut like on all two strokes with ports, the more you hone, the more cylinder starts to conform to where the least amount of material is. And it will start to remove more material where that least amount of material is. So around the ports and skirts, the more you hone, the more it out of round it can become. On a standard 4 stroke engine block, its not an issue since there is solid material the full length of cylinder. It takes some practice and finesse to keep a two stroke bore straight and round. Changing the rpm, stoke speed, and load on stones greatly affects the outcome of where material is removed. Its easy to hourglass or barrel the cylinder. The more material removed, cylinder started to egg at bottom because the skirts hanging down. They actually flex under pressure from hone stones. So if you know anybody that uses a three stone spring loaded style hone to "fit" a piston, needs to get a reality check. It aint gonna work with any precision needed to achieve good ring seal. When properly done and rings are well made you will have same compression readings when first fired up as when motor has 10 hours on it. Many people dont get maximum readings until many hours of running. Enough for the hot air. Lets get back to the "boring" cylinder.

    The piston diameter measures right at 3.5215" with micrometer. Whats nice here is it doesnt matter if micrometer actually reads correct dimension or not. But it does work just fine to use the spacing to set a dial bore gauge.

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    This is a micrometer thats adjustable from one to six inches. It has changable ends to get desired range. Dont have to calibrate for the purpose in question here. Just measure the piston and lock in place.

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    What is very important is setting the dial bore gauge correctly. This will make or break your measurements. The gauge is set to zero on dial. This is the actual diameter of piston. This is a check recheck and check again. Before each time you use the dial bore gauge, you check it once more.

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    With the bore gauge set to zero on dial as actual dimension of piston, the needle will rotate counter clockwise and bore increases in size. You can see this cylinder is 0.0045" larger than piston diameter. Its bored out to 0.001 smaller than finish. It only take a few strokes thru cylinder to reach finish size. Very little pressure is needed on stones also. This is the easiest way to achieve a perfectly round bore from top to bottom. The HARD part is using the boring bar and reach the dimension so close to finish size. One slight mistake and you go oversize and have to go up to a larger piston. For just regular recreational use, SBT recommends 0.007" to 0.008" clearance. Thats good if I missed the dimension I was shooting for. Then just hone without exceeding the max clearance recommended. But I dont care to run any piston that loose. Its a guarantee for broken skirts after a 100 hours or so.

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    After running the Sunnen hone thru for just a few moments, I have achieved the desired finish size. Piston clearance is right at 0.0055". With just some patience and common sense, the cylinder is bored close to finish size then honed with minimum amount of actual machine work. Going slow and then approach the desired dimension without mistakes. Its finished and ready for the next step.


    If there is another picture below↓↓↓↓↓? I have no idea why its there or how to get rid of it. When I am logged in and access this page, this large pic is hanging there. But on eidt it does not show to exist. Maybe just my imagination, I dunno. Do you see it too, or am I going crazy?↓↓↓↓
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    Last edited by Seadoo timebomb; 10-11-2012 at 02:25 PM.

  12. #20

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    Since this ski is strictly for recreational use, its useless to do any comprehensive porting. It would be a total waste of time. There is one area that deserves some attention tho. This small ledge of aluminum on top of exhaust port as seen where arrows point. On some cylinders its almost non existent On this particular one its was noticeable enough I chose to do something about it. For the Dremel guys, you have a mission. All that needs to be cleaned up is aluminum that hangs down into exhaust port opening. You dont need to alter anything or raise port or change angle. Just remove the aluminum until it blends with the iron liner. Do equally on both bores. Its easy and you can use however means you have available. A file, die grinder small flap wheel, or tootsie roll. I used an extended 1/4" carbide burr and then cleaned up with a tootsie roll on the same die grinder. Took only a couple minutes on each port. When the iron liner started showing grind marks, I stopped and blended with the emery cloth tootsie roll. You probably wont realize any gains in top rpm readings, but not removing the small ledge is same as having your rave valves not opening completely. At least by the amount of material removed. Not much, but when raves are not working, its very noticeable. Anything to improve the flow characteristics here is a plus.


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    Here is a close up before the cleanup.

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    This one is done. Not much needs to be removed. Just enough to blend into the liner.

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    Now both finished and equally cut.

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    If you feel compelled to cleanup all of the port openings where liner meets aluminum, go ahead. It wont hurt. Even tho the intake ports are not usually a perfect match, it doesnt affect flow in the slightest. You will not gain any noticeable or magical horsepower. But it can be good for the soul. Sometimes just for the peace of mind is enough to make you think it feels faster.


    OK the same thing again. ↓↓↓↓↓↓ I removed this pic from above and now it shows up below large at bottom of page. ↓↓↓↓↓↓ I think the page editor is possessed.
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    Last edited by Seadoo timebomb; 10-11-2012 at 02:42 PM.

  13. +1 by:


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