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seized my 850 two stroke (then freed it), why?

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  • seized my 850 two stroke (then freed it), why?

    Hi Guys

    A little help please guys, my motor is sick and I want to make it feel better!

    Facts first, my motor is a merc in-line 4 cylinder 2 stroke, model 850, 85 hp, vintage about '79, serial # 7071754. I bought it about three years ago, with a rebuilt power head. The boat is a 16' fibreglass bow rider, vintage about '75.

    Last weekend I got the boat out for maiden voyage of the season. Charged the batteries, greased the engine fittings, checked the lower unit oil (clean), checked for oil in the gas (by colour, plus I always add it when I buy gas), checked the bilge pump and horn, then went to the ramp.

    Boat started just fine (on a new tank of gas), and went like stink about 10 miles down the shore of Lake Ontario to Port Credit for lunch with my buddy Dave, then after that it went like stink back (the lake was super flat, which is very unusual on such a big lake) to the ramp and about 3 miles short of the ramp the gas ran out so I switched tanks, went like stink again but just about 100 yards short of the ramp the motor suddenly made a squeaky noise and then stopped. Tried bumping it with the starter but it wouldn't even turn over.

    Dave and I paddled in to the ramp then took it home. Took the covers off and found the flywheel was not moving. Took the plugs out and saw what you would expect, four dark holes..... Wrestled with the flywheel and got it to turn again. Squirted some oil into each cylinder and turned it by hand, then bumped it with the starter, it turned easily.

    I poured some of each of the three tanks of gas into shot glasses and the colour looks almost identical so I'm guessing there is oil in each of the tanks. When the gas evaporated something funny happened, two of the glasses have a yellowish residue while the third remains blue. Why? Is this a clue to my problem?

    Yesterday I checked compression, on cylinders 1,2,3,4 it was 140, 145, 145, 145 psi cranking the motor as-is. The test kit said to squirt some oil into each cylinder and check again so I did, the results were then 163, 170, 165, 165 psi.

    As far as I know this means there is a small amount of leakage around the rings (thatís what the oil is supposed to improve on), but not enough to worry. Cylinders are considered the same if the total difference is not more than 10 psi and not more than 25% of the highest compression.

    So this test showed nothing of interest, except that the motor did tighten up right at the end of the testing, which makes me think the problem may be on the crankshaft end rather than the cylinder end. I donít know which way to go now so Iím posting these results here to see what opinions I get.
    Attached Files


  • #2
    Re: seized my 850 two stroke (then freed it), why?

    OK, First of all your compression is excellent, so you dodged a bullet. The seizure of the motor was likely caused by overheating or water-alcohol seperation. Let your tanks sit ansd then siphon a gallon off the bottom of each tank into a clear container. If it does not have the oil color, discard it since it is water and alcohol.

    When was the last time the waterpump impeller weas replaced. If more than 2 years ago, then change it now.

    Comment



    • #3
      Re: seized my 850 two stroke (then freed it), why?

      Someone could of put sugar in your tanks?

      Comment



      • #4
        Re: seized my 850 two stroke (then freed it), why?

        Burn a spoonful of the gas. If it leaves a caramelly gooey residue, it's been sugared. I've had it happen to me.

        You dodged a bullet. Find out if it's bad gas, poor cooling, or what before you run it again.

        hope it helps
        John

        Comment



        • #5
          Re: seized my 850 two stroke (then freed it), why?

          to Chris1956
          Thanks for the input, I'll test the gas like you suggest. The impeller hasn't been replaced in more than 2 years so I'll do that too. I hope that's the end of it but somehow I still don't feel good about this yet....

          to Meet
          Could have, there wasn't any physical security on the boat or the gas tanks but I'm not aware of anyone who has a grudge against me or my buddy enough to do a silly destructive thing like that. It was stored in a good rural neighbourhood where half the neighbours are related to my buddy in one way or another.

          to j_Martin
          I'll do the burn test too and see how that goes. I agree with trying to find a cause before trusting the motor again.

          Comment



          • #6
            Re: seized my 850 two stroke (then freed it), why?

            to meet and j_martin

            Burnt residue didn't have any amount of sticky junk left over for any of the three, so sugar doesn't look like an option. The suspect tank didn't leave any soot, and did have a drop of water. I think I know the problem now. The colour was wrong, the suspect gas burned slower and much longer. Photos attached, see the next post for what the problem appears to be.
            Attached Files
            Last edited by Wreck Rider; May 10th, 2008, 11:32 PM. Reason: add photos

            Comment



            • #7
              Re: seized my 850 two stroke (then freed it), why?

              to Chris1956

              Thanks for the tip. When I took a grab sample from each tank, from the surface, I missed an important point. A photo is attached showing grab samples taken like you suggest (but with a big syringe and long stiff tube to reach the bottom).

              I'd never heard of this alcohol separation issue before. Judging by the colour of the gas, I was running straight gas and alcohol for about 3-4 miles.

              I hope I can just get this running again with a tank of the good gas.

              Is it a good idea to over-oil the first few tanks to wear off any little burrs that I created in the cylinder or on the cranks?
              Attached Files

              Comment



              • #8
                Re: seized my 850 two stroke (then freed it), why?

                Extra oil will have no value. Make sure you have removed all the alcohol-water mix from each tank. Test the new gas by adding the oil, mix and let stand for a while. Now get a sample from the bottom as before.

                The gas station may have water in t's tanks as well.

                Comment



                • #9
                  Re: seized my 850 two stroke (then freed it), why?

                  Originally posted by Wreck Rider View Post
                  to meet and j_martin

                  Burnt residue didn't have any amount of sticky junk left over for any of the three, so sugar doesn't look like an option. The suspect tank didn't leave any soot, and did have a drop of water. I think I know the problem now. The colour was wrong, the suspect gas burned slower and much longer. Photos attached, see the next post for what the problem appears to be.
                  Alcohol (pure) burns with a colorless flame, and is cooler than gasoline.

                  That's mostly alcohol and water.

                  You found it, the dreaded phase seperation.

                  John

                  Comment



                  • #10
                    Re: seized my 850 two stroke (then freed it), why?

                    Another update.

                    I cleaned out the bad tank of gas today. Poured out the clean gas on top into a pail then put the last gallon or so into a clear jug. Lots of separated phase. Check out the crazy amount of lower phase in this picture. Plus, I already took out 8 oz or so the other day, plus whatever amount we burned in the engine. An amazing amount really.

                    I sampled from the bottom of the bucket after some settling time to be sure there was no separated phase there then treated it with a dose of gas stabilizer. The photos show what it looked like when sampled from the top and from the bottom of the pail.

                    Cleaned the tank by getting all the fluid out with a syringe and tube (thereís a ridge around the filling neck of the tank so you canít pour all the fluid out, donít know why). Then rinsed with a small amount of acetone, syringed that out, mopped up the last little bit with a paper towel on a stick, then air dried with vacuum cleaner. Poured the clean gas back in the tank with a little extra oil.

                    Now Iím ready to take the boat out, with good gas, and do donuts within 100 yards of shore and see what happens.

                    Personally I think this episode is almost over. A sea trial is really an important part of confirming that though!
                    Attached Files

                    Comment



                    • #11
                      Re: seized my 850 two stroke (then freed it), why?

                      See that chit in the water just below the gasoline. That's what usually causes the most problem. Plugs up small passages, like jets, or the screen in the cheep murkery filter, and starves a cylinder long enough for it to overheat and stick.

                      On my XR4, I prevent it from ever being an issue by running all the fuel through a water seperating fuel filter. (RACOR)

                      hope it helps
                      John

                      Comment



                      • #12
                        Re: seized my 850 two stroke (then freed it), why?

                        Wreck, Two observations.

                        Your premix is a nice tropical color!

                        Your wife does not know you have the kitchen glassware in the garage, does she?

                        Comment



                        • #13
                          Re: seized my 850 two stroke (then freed it), why?

                          to j_martin

                          Good point about the chit, I'll have a look at the filter before going out.

                          Comment



                          • #14
                            Re: seized my 850 two stroke (then freed it), why?

                            to Chris1956

                            Thanks for noticing, it reminds me of my first trip, to Georgetown on Exuma in the Bahamas.

                            Ssshhh!! Until she decides to become a member of iBoats and check out these posting our secret is safe.
                            Attached Files

                            Comment

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