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  1. #1

    Join Date
    Jul 2011
    richmond, va

    Mechanic input requested engine issues- issues with 99 xl700 with blown cylinder

    Hi all. Yesterday I purchased a 1999 xl700 with a blown cylinder as a project. I tore it down and found piston damage on the rearmost cylinder. I have a number of questions that I am curious of and was hoping for someone who could look at some pictures may be able to help me figure out. I want to rebuild it as economically as possible but dont want to miss something in the process.

    My hope is to replace just the top end without having to change the whole short block. I am concerned about the underlying cause. Im not sure what normal conditions are on these so I want to make sure Im not missing something obvious. Observations I have made:

    What appears to be some salt accumulation inside head and exhaust system pipes.
    piston damaged around top and outside edges (0 compression), apparent jamming of piston with change in shape of ring area (see photo)
    some damage to inside of the head (see photo)
    some grooving in the head on the rear cylinder
    Green oil (what is being used in the oil reservoir is accumulated to some degree in the front of the crankcase) and looks clean.
    Little to no oil accumulation in the crankcase under the rear cylinder and black in color.
    No visible debris in the rear of the crankcase under the broken piston, everything looks visibly okay, no apparent issue with the cranks on either side. Speculation is that damage is contained to the top end of the motor
    What appears to be a tiny hole in the interior of lower crankcase (see first photo). Doesnt look like it would cause an issue but unknown.

    With the thought in mind that the purpose of this ski is to be used a few times a year, for playing with my younger children on a freshwater lake and to replace my current 20+ year old seadoo.... This is not a performance ski or performance situation.

    Here is what I am trying to find out.

    1. Thoughts on possible cause (normal failure?). speculation is heat buildup from restricting cooling and/or unusual oil delivery to cylinder.
    2. Is it normal to have oil in the crankcase in these? I see what appear to be oil passages in the crankcase. Is it put in there or normal accumulation from the mix lubrication. The fact that its in the front and looks to be clean raw oil with nothing in the rear crankcase makes me wonder whats normal. wondering if some detonation or burn getting rid of whats in the rear from the piston or if something is out of whack in the front.
    3. Should I be checking or blowing out the small passageways in the crankcase with compressed air to make sure they are not clogged or clean the crankcase?
    4. Is the imprint/damage on the head an issue, should it be somehow cleaned or polished and if so how should it be done.
    5. Is the buildup in the cooling area excessive? Is there a way to clean out the salt buildup in the outside cylinder wall and/or exhaust or is it necessary or recommended. I would assume so and my thought was a pressure washer but wanted to make sure Im not doing something stupid.
    6. Should I abandon the oil pump and go with premix if there is some question on the pump?
    7. With the little available information is available, is a top end kit the suggested solution? any thoughts on shops? was looking at sbt and fullboreonline.
    8. is a carb rebuild suggested at this point. Dont know anything about how this ran with the previous owner
    9. Is the hole in the upper left area of the last photo an issue or just a casing issue when poured?
    10. Is the head damage an issue? If so fixable or replace?

    Any input would be appreciated. Thanks!

    in the event that the photos dont show up the link to the picaso web album is here:

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  2. #2
    With that kind of damage i would pull the motor, there has to be pieces down in the case, or in the bearings, check to see that your crankshaft bearings are not shot, you have something that came apart and went up into the cylinders or rings that broke.

  3. #3

    Join Date
    Jan 2006
    Texas City, Texas
    I am not a mechanic, just a rider. I will tell you though that it appears to have been run hot for some time. If this is true, then the underside of the crown of the piston will be black as well. What the underlying cause for this is, I do not know. It could be the wrong plug (heat range), bad fuel with lean carbureton, or just a plain (rear) seal leak. Yamaha's have really good cooling systems, and even though yours appears to have been neglected for some time, it is hard to believe that lack of cooling on the water jacket sides are the issue.

    I know that you really do not want to put a lot of money in this thing, but you are right in considering all of the potential things that you might miss.... especially with a 12 year old boat who shows signs of neglect.

    Two strokes are simple compared to the 4 strokes, but much less forgiving when you make a mistake. This little engine may be full of alligators that when you deal with one, another one completely unrelated to the original problem will come out to bite you.

    The crank may look fine, but it is a 12 year old crank in a salt environment....etc.,etc. I would recommend a complete overhall to eliminate those types of mistakes and headaches.

    In fact, I would recommend that you package the whole engine up and send to to Group K ( They specialize in 2 strokes and their operating philosophy is centered around reliability. They would make all of your stock components better than new. Things like reshapeing the domes and milling the head, boreing the cylinders, cleaning up the carbs and making sure that they are operating properly etc. They work with your stock components and make them as good as they can be.

    I really am passionate about seeing riders ride rather than turning wrenches. It would be simple for a do -it-yourselfer to replace a head or cylinder, but this particular engine needs to be gone all the way through it. Since all of this work needs to be done anyway, the only difference between you doing it and them (Harry and Gerhardt Klemm) is their labor. Imagine you spending hundreds of dollars and weeks of your riding time to get this thing running just to have it break down over something you never accounted for. On the other hand you spend a few extra hundred bucks and you have a bullet proof engine for a few years till those kids of yours can ride that thing on their own. Now the real truth is somewhere in the middle of those two extreems.

    Trust me, it is money well spent.

    By the way, welcome to the forum

  4. #4
    Well said Salty

  5. #5

    Join Date
    Jul 2011
    richmond, va
    Thanks for the input guys. I ended up sending the top end to the guys at fullboreonline earlier this week. The discussion I had with the machinest up there on the condition of what I was seeing he thought that an top end rebuild would suffice. I am going to take a shot at it and hope Im not wasting time and money. I bought the ski for 800 w/trailer and otherwise it seems to be in very good condition. Hopefully it was a good deal (any input on that?). Thought it would make for an inexpensive project bike for something that appeared to still hold a book value well in excess of that. I have had my old sea doo for almost 20 years now with very little maintenance but its just too small for tikes. Im hoping that this one with a careful break in on the top end will last for a few outings a year for 6-8 years pending no other bugaboos surface . Im anxiously awaiting their assessment of the problem with the piston to see if they can ascertain any other underlying issues. My thinking was worst case I should be able to resell it at the same price I paid for it if I destroy my new top end and dont feel like dealing with it any longer without soaking too much of a loss :/

  6. #6

    Join Date
    Jul 2011
    richmond, va
    Salty forgot to ask, what do you mean by "just a plain (rear) seal leak". Dont know what you are referring to and how I might look for that. Is this at the camshaft/prop shaft? (ie mechanical and or lip seal to keep water out of the engine or are you thinking about some type of coolent leak out of the engine?

  7. #7

    Join Date
    Jan 2006
    Texas City, Texas
    Quote Originally Posted by mwinschel View Post
    Salty forgot to ask, what do you mean by "just a plain (rear) seal leak". Dont know what you are referring to and how I might look for that. Is this at the camshaft/prop shaft? (ie mechanical and or lip seal to keep water out of the engine or are you thinking about some type of coolent leak out of the engine?
    We are talking about the crank seals, front and rear.

    This is a direct quote from Group K:

    Air Leaks - The lower end of your engine should be totally air tight up to 8 psi. New engines pass this test with no problems. However engines with older deteriorated crank seals or brittle intake gaskets can allow outside air to leak into the lower end during operation. This "air leak" can make the fuel mixture lean enough, at high rpms, to cause a piston seizure. Air leaks, not engine modifications, are by far the number one cause of piston seizures.

    As I was saying before, you may be repairing a 12 year old boat thinking I'm fixing the problem, but in reality, just treating the symptom. You are fixing the top end, but the top end may have been distroyed by a leaking rear or front seal. That engine potentially has lots of aligators that will bite you, and they will come at you from a direction that you are not even thinking about. Having a professional rebuilder (like Group K) addresses all of the "alligatiors" that we don't even consider, not just from an "old engine" perspective, but also from the perspective of a particular model which has certain inherent weaknesses that must be addressed to make it reliable.

    You bought that boat "right" meaning that if you were to spend as much as 1200 having that engine completely rebuilt, then you would have 2000 total tied up in it, and STILL would not be hurt. You could get every dime back if you just decided to turn around and sell it after it was repaired. If you were capable of taking care of a unit for 20 years, I guarante you that a Yamaha will last just as long with that type of TLC.

    Just my opinion.

  8. #8

    Join Date
    Jul 2011
    richmond, va
    Thanks again for your information. Interested in maybe going farther on this then. If I already have the exhaust and head off the unit, is removal of the lower unit just a matter of basically removing the four motor mount bolts, sliding it forward to release the shaft coupling and flipping it over to split the housing? Assuming at that point it would be simple to replace all the seals, possibly bearings, and inspect the shaft and make sure that there is no debris within the case? There was no real visible debris in there and I was flushing the shaft with small amounts of light weight motor oil and a syringe looking for any evidece of issues. there was either some very small flecks or possible small air bubbles in the oil I was retrieving (hard to tell).

  9. #9

    Join Date
    Jan 2006
    Texas City, Texas
    You are correct on how to remove the lower unit, but you forget about the flywheel, electrical wireing, and starter, oil pump. None of these components are difficult with the exception of the flywheel at times.

    You are treating this as if the seal were the problem, but you have also mentioned the carbs (which are just as big an alligator). Yes, they should be rebuilt. You may not have considered that an oil line may have fallen off of a carburetor which distroyed your top end. This happen often in older units. Oil in the hull is a tell tale sign. Yes you should trash the oil injection, simplify and go premix to eliminate that gator.

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