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Success Of Rebuilds From the Top?

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  • Success Of Rebuilds From the Top?

    Since this is my first experience with a piston failure I am curious as to the success of Top Rebuilds especially when it appears to be only a piston, and sleeve.

    I have a very strong mechanical background, and therefore recognize the importance of locating the cause.

    I don't mind investing a couple hundred dollars and a few hours replacing the destroyed parts verses a total replacement.

    What is the "rule of thumb", and/or vast experience with top rebuilds, and their worthiness?

    Thanks,
    JCH

  • #2
    Re: Success Of Rebuilds From the Top?

    I don't know what the succes rate is, but if I had it to do over again, I'd go with a new SBT motor. Their 1 yr. no-fault warranty is unsurpassed. Obviously, you need to determine the cause of the problem and fix it - or you may end up toasting another motor. Good luck!
    "Helping you make smart choices about your money - so you can live a better life."

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    • #3
      Re: Success Of Rebuilds From the Top?

      first thing you gotta do is pull the top end off and see how bad it is. if the piston came apart at all then it has contaminated the crank and you should not trust it. it is a rare thing for a watercraft engine to go without going all the way. here is a pic of an 1100 motor that was running (not very good)when i tore it down. wild huh
      Attached Files

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      • #4
        Re: Success Of Rebuilds From the Top?

        I was lucky enough to have shut the engine down prior to severe damage though in pulling the cylinder box I know some debris has fallen into the crank housing.

        I am considering replacing the cylinder sleeve and piston assembly. Rod, and crankshaft retain their original color, and very minimal damage to the head.

        It appears to me as though this situation may warrant a top rebuild verses a reman even though I am a firm believer in starting fresh verses a patch job.

        Since I have 2 good piston, rings, rods, crankshaft, and head it seems wasteful to not at least try the piston/sleeve replacement first.

        I certainly do not wish to waste my time nor spend wasteful monies, but if top rebuilds in 65U Yamaha engines have good success ratio based upon minimal damage it certainly may be worth the effort.

        I recognize SBT is primarily in the business of selling remans, but I can't imagine SBT would recommend to replace verses repair under these circumstances. Obviously if the repair should be inaffective or troublesome I still have the opportunity to reman.

        Isn't it worth a try?

        Thanks,
        JCH

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        • #5
          Re: Success Of Rebuilds From the Top?

          At this point the cases need to be split and the bearings on the crank inspected. If good them you can re-use the crank. I always split the cases to inspect the crank anything else is pure speculation. Always use new seals and gaskets.

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          • #6
            Re: Success Of Rebuilds From the Top?

            i bet you play the lottery too if your heart is set on only doing the topend at least do all three holes. if not i will bet money that you dont get more than 10 hrs out of this patch job. if there is any head damage at all just think of the beating that rod bearing took. hate to sound so negative but you asked

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            • #7
              Re: Success Of Rebuilds From the Top?

              John,

              No I don't play the lotto.....don't have to, but my impression of a top rebuild was just that, pistons, sleeves, and rings, therefore my question with respect to top rebuilds and their success seemed a valid question. I certainly understand my options with respect to a total breakdown, but why would I want to even consider the task since the reman option would be far less consuming.

              The boat is a new aquisition from an one owner senior adult who used it rarely. I had gone over most all systems prior to using same, but obviously there was something I missed. I suspect a lean carb, which showed up during my testing of the boat shortly after purchasing it. I shut down the engine as it began to drop rpms thereby minimizing catostrophic failure.

              I understand my choices:

              Top Rebuild
              Total Rebuild
              Reman
              Factory New

              This isn't a question of money, it is a question regarding when to do a top rebuild.

              Thanks

              JCH
              Last edited by JCH; 07-07-2004, 07:00 PM.

              Comment


              • #8
                Re: Success Of Rebuilds From the Top?

                Top end rebuilds are fine. As long as your crank is ok and you don't need new crank seals, replacing piston and sleeve should be fine. The cause of 2 stroke failure if often an air leak , a clogged cooling line, or pre-ignition. Check out the technical article on piston inspection. It should help you find the problem. Don't be so paraniod.
                Never underestimate the power of stupid people in large groups!

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                • #9
                  Re: Success Of Rebuilds From the Top?

                  Poser,

                  Thanks for the reply, and encouragement. I suppose there are no guarantees in life, except of course with SBT. I'm not nearly as paranoid as I am curious.



                  Thanks

                  JCH

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                  • #10
                    Re: Success Of Rebuilds From the Top?

                    I'll put my 2cents in here.

                    When I bought my blaster from a friend,I was new to the pwc world.He told me that he had done a top-end rebuild.And the ski ran perfect...but not for long.He stated to me that the lower corner of the piston was missing and that it probably blew out of the exhaust. 3 rides later she locked up.Rod bearing failure,snapped the rear rod.

                    Now,having spent 5 years and many certificates in the bearing and PT business,I have been through many trainings as to the causes of bearing failures.The leading failure is due to contamination.It only takes one little spec of foriegn metal/sand to completly destroy a bearing.If you can imagine how a bearing works,it rolls on three surfaces.The surface of the roller,the inner race, and the outer race.One mark on any of these surfaces will leave a mark on the opposing surface,then the next,then the next,and so on and so on.

                    My point is:If there is just one peice of anything left in you case,it will eventually get picked up into the bearing,causing damage,and eventually failure.And from the looks of the pics,there is alot of debris in that motor.

                    As torquenut said,you must still completly disassemble the motor,and thoroughly clean and inspect everything(and lube bearings upon reassembly).However,you cannot actually see the bearing surfaces that I mentioned earlier,so they are rather impossible to inspect.But if you have any foriegh material in the bottom of the case,it has most likely made its way into the crank or rod bearings.

                    On top of that,I also have 5 years experience in heavy duty mechanics.And have rebuilt every motor from 3cyl perkins to v8 detroit deisels.

                    I have the original 701 in my shop(in pieces) atm,and am planning on rebuilding it,but it is getting all new internal parts...top to bottom.

                    I am currently out of the mechanical field,and work for WeatherShield windows and doors as thier service and warranty tech for the west-central part of Florida.But still love to mingle with my own and friends mechanical problems.

                    Hope that helps make your decision.
                    Visit www.pwctoday.com for techical help

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                    • #11
                      Re: Success Of Rebuilds From the Top?

                      Skraggy,



                      I appreciate your input, and your advice is noted!

                      How do crank bearings deal with normal wear shavings as most engine blocks will acquire over time? Same situation I imagine and ultimately those shavings play on the bearings as well which ultimately cause a major failure, or are shavings less distructive then actual particles?

                      Great to have the experience of others prior to undertaking such a project.

                      I appreciate all this valuable free information!!!!

                      Thanks,

                      JCH

                      Comment


                      • #12
                        Re: Success Of Rebuilds From the Top?

                        Well,If you are speaking of the normal wear of an automotive engine,and the shavings(or dust) that builds on the bottom of your oil pan.The answer is simple.There are not roller bearings in most auto engines.And the metal settles on the bottom of the oil pan or to the drain plug,which has a magnet in it.

                        If you are talking about the normal wear of a 2-cycle.The particles are usually so small that they get carried out with the exhust flow.Larger particles are not a good thing to have floating around in your motor case.If you have that much debris up top,as I seen in your pics,chances are that some of the larger pieces made it to the bottom.

                        I would definately split the case and inspect and clean the bottom.Dont just rebuild the top and assume the bottom is good.If you see shavings on the crank and rods,its in the bearings also.

                        NP on the help

                        Hope it works out for ya,
                        Visit www.pwctoday.com for techical help

                        Comment


                        • #13
                          Re: Success Of Rebuilds From the Top?

                          I have had simillar damage to GP1200 65u and split cases and found no debree in engine.
                          Im waiting for cylinders to come back from dealer after a fresh bore.
                          I will be installing a aftermarket head instead of stock.
                          I also recomend a thourough inspection off the exhaust as you dont want to suck anything back into the engine if you backfire on initial start up.
                          I bought 99 GP1200 and Destroyed piston in #1 cylinder after 1 tank of gas.
                          I was returning to the dock after test drive.
                          Person I bought from had BR7HS plugs in instead of BR8HS and when I questioned him on this he denied any knowledge of a different heat range plug.
                          Also denied any knowledge off engine problems.
                          1200 only has 75 hours and I feel he knew of problem whan he sold it to me.
                          I wish you luck if you do a top end rebuild and deffinetly inspect bottom end and exhaust.
                          If you are compitent machanicaly you should be fine.
                          If you find anything questionable seek a knowledgable source for information and inspection.
                          SCOTT...
                          Attached Files
                          Last edited by ScottD; 07-13-2004, 12:14 PM. Reason: To add picture.

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                          • #14
                            Re: Success Of Rebuilds From the Top?

                            Thanks all.... for the continued advice. Skraggy.... the pictures listed are not mine or of my engine. My damage was no where near that bad.


                            JCH

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                            • #15
                              Re: Success Of Rebuilds From the Top?

                              You will have NO problems using BR7HS on a 65U or a 63M for that matter.
                              J-me
                              05 Bayliner 175
                              98 GP 1200 Yamaha factory support hull, Lamey engine, Skat pump

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