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  1. #1

    Join Date
    Sep 2011
    Phoenix, AZ

    New to this and screwed up my 750 zxi. How extensive should rebuild be?

    So being new to Jetskis but not new to wrenching or forums, I thought I would sign up here and see if y'all are as knowledgeable about skis as my buddies and I are on my diesel forum and see if I couldn't get a little advice.

    Bought a pair of 95 zxi's this summer. 900 and 750. Really clean skis, especially the 750. It was a virgin... until I pulled a major bonehead move. After having carbs professionally rebuilt, and watching and asking a ton of questions so as to start gathering knowledge, we had many a fun weekend with them. Labor day weekend I decide (after missing a weekend prior), to start the things in the driveway the day before... taking some folks out and wanna be sure everything is up to snuff, y'know. I know not to run them for more than 15 seconds at most without water. What I DIDN'T know, was NOT to run the water without running the skis, which I did. All seemed okay though until we got to lake next day. Wouldn't run right, and wife and kids and guests kept insisting on trying. I didn't find out about not running water until after the lake incident or I would never have gone. Had no idea I had just screwed up my equipment.

    So I finally got around to looking into them. Compression test showed I had problems. Popped head off the 750 and here is what I have. My question is, how far should I go on this? My initial thought is a top end, but I don't know for sure my little stunt is what caused what you see. Should I be investigating further, and if so, for what? Obviously the rear cylinder got real damn hot (never got a light though), and I have read that it is an known issue with these.

    Any advice based on experience would be appreciated. I want to do it right and have a solid, reliable ski again.

  2. #2
    It looks like you got water in the greyish cylinder to me, likely through the exhaust port, since it appears there is slightly more damage to the exhaust side. It is hard to tell from just the pictures of the top of the piston. I could give you a better opinion if you pulled the pistons and took pictures of the cylinder walls, piston exterior, and piston interior. Your going to have to at least replace the one so, your not going to hurt anything by taking it off.

    The golden cylinder may just have a rich burning spot in the middle. My dirt bike does this, but runs fine. The way to see if it got really hot and overheated would be to check the underside of the piston and see if it looks black above the piston pin. When a piston overheats enough it gets so hot the oil on the underside burns to the bottom of the piston. It will be black like on the top if it overheated. If it overheated, there will possibly be some marks on the cylinder with some scoring from the piston expanding too much. It may be fine.

    You definitely will want to replace the greyish piston (may want to replace both while at it) and be sure to clean out the crank case. Some people flush it with kerosene or diesel fuel. I have flushed it with basic 4 stroke motor oil. It will take at least 5 flushes before the stuff starts cleaning up. I will likely have a grey ting to it from the shrapnel that ground up. You will need to check for any vertical play in the crank shaft, rod, and bearings and any other wear service limits possibly reached. The limits will be found in a manual. You can usually buy an electronic copy for $2 on ebay. If there is too much play you will need a crank rebuild or a new one.

    If the cylinders are scored up beyond the service limit, you will have to bore out the cylinder and put in an oversized piston.

    I just had a piston disintegrate due to water on my 96 900 zxi and had to get a new cylinder $$$$$$$ because mine had been bored out all the way. It was all due to a gasket that failed on the exhaust manifold. I am putting the rest of it back together tomorrow and giving it the first test. You are fortunate you only have 2 jugs to worry about. That will definitely save you some $$.

    This is a start. I know it is a lot, but I wanted to be thorough. Let me know if you have any questions or need further explanation.

  3. #3

    Join Date
    Sep 2011
    Phoenix, AZ
    Thanks so much. I actually have 5 jugs to worry about... have a 900 that is showing garbage for compression now... 65,75, 70. I'll tackle that after this one. Ugh. I was already planning on doing both pistons while I am there. How do you prefer flushing the bottom end of these? I am having a small procedure, then leaving town for the minor recovery so I can see some family & friends, and will tackle this when I get back. I may get time today to pull the jugs, and if I do I will post up some pics.

  4. #4
    Honestly, I have only flushed the crank of two engines (a dirt bike and my 900zxi). Just got the zxi up and running today. The dirt bike has been running strong for a good year and I abuse the heck out of that thing. Both times I used 10w-30 because it was available and I didn't have to go to the store to get it. I have never tried diesel fuel or kerosene but most people I hear use kerosene as a preference. If I had kerosene sitting around, I prob. would have used that. I have heard either way you will have to flush it through real good at least 5-7 times.

    Procedure I used:
    I poured enough oil into each crank hole to fill it about half way. I then turned the engine over using my hands/fingers on the rods until the oil got fairly dirty. I then dumped the oil into a pan and refilled with clean oil. After repeating this process about 4 times, I added a step. After I drained the dirty oil, I sprayed out the inside with a cleaner (ie carb cleaner or similar). This helped get the extra oil that stuck at the bottom. I did the process with the extra step a total of 3 times. If you use kerosene, you may not need to add this extra step.

    I did not do every flush on all three cylinders. I stopped flushing the individual cylinders when I could put fresh oil in and turn over the engine for about 2-3 minutes and not have it get dirty. After getting all the cylinders clean, I did one final flush filling all cylinders and turning it over for about 3-4 minutes just to get any excess.

    This may not be the best method, but it worked for me, and everything turned out pretty clean and looked ok.

    Let me know if I can help you any more when you get further into things. Hope your procedure goes well.

    P.S. Where do you ride at out in phoenix? Lake Mead? Page? I was thinking about moving out to the sedona/flagstaff area some day and was not sure if it would be worth hauling the jet ski out.

  5. #5

    Join Date
    Sep 2011
    Phoenix, AZ
    Oh, definitely worth hauling the ski out to AZ! Looong riding season... year 'round if you are in the Phoenix area and don't mind using a suit. Lot of the serious guys ride all year. I personally live in the N. end of Phoenix, so I ride at Lake Pleasant. It's about 30 minutes from my house. There are several lakes in the valley, as well as throughout the state. If you move up north there are a few up there as well. Mormon lake comes to mind. Sedona is gorgeous. Small town with millions of tourists every year, but an absolutely awesome area. If you love the outdoors and can make $ in Sedona or don't need a city to make your money, Sedona is amazing. I'm still drying out from too many years in the NW, so I am loving Phoenix and the lack of precipitation.

    Thanks for the advice on the flush. I'll be pulling the engines when I get home. Got a couple dirt bikes needing attention as well... Daughter blew up her CR80, got a TTR down with electrical problems, an RM project I need to get moving on, and I sold my KX because it was pissing me off and was tired of it breaking more than riding. When it rains it pours!

  6. #6
    steve45's Avatar
    Join Date
    Feb 2008
    One of the big problems when cranking an engine with water in the cylinders is bending a rod. Check that the pistons come up to the top of the cylinders, and look carefully at the rods when you remove the cylinder block.

  7. #7

    Join Date
    Jul 2010
    blue springs , mo
    make sure you go thur the carbs and the exhaust pipe to see what caused the problem. the worst mistake everyone makes is they put the engine back together and never mess with the carbs and i time to the lake they blow it up again, so make the cautious decision and go thur the carbs. check the exhaust for piston fragments.

    ohh I use a solvent tank to flush my motors to get fragments out if i take the engine out. If i leave the engine in i will use compressed air to clean the crank. but watch out for your seals.

  8. #8

    Join Date
    Sep 2011
    Phoenix, AZ
    Good advice, thank you. The carbs were just rebuilt only a few rides before the labor day weekend debacle, and I did go through them first before discovering the water in exhaust damage. Haven't got to them yet, but did get one of my bikes running last night! Little wins.

  9. #9
    PoppaRo's Avatar
    Join Date
    Aug 2011
    Coastal Georgia
    sorry to hear about you bad luck with your toys.did they truly hydrolock? if so the crank could be out of spec too

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